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S-Block Amlan Nag (BTech, MTech (Univ. Of Alberta, Canada)

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Chemistry is the basically related with the study of elements.These elements are classified in some categories and the two most important categories of the elements are known as representative elements. Representative elements of the periodic table include s are p block elements. s-block elements included the elements of group 1 and group 2 of the periodic table while p – block elements include the elements of group 13, 14, 15, 16, 17 and 18. s- block elements arte all metals on the other hand p- block elements are mainly non-metals but they include some metalloids and metals also. The s and b lock elements have a great role in chemistry and also our life. As we will study the properties of all these one by one in this chapter will be able to know about the great importance and applications of these elements.

The elements in the long form of the periodic table has been divided into four blocks, namely s, p, d & f blocks. The elements of group I & II receive their last electron in s-orbital. So they are called as s – block elements.

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The metals Lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs) and francium (Fr) which have one electron in their outermost shell belongs to group I and are called alkali metals as they react with water to form hydroxides which are strong bases or alkalies. The elements of group II are Berryllium (Be), Magnesium (Mg), Calcium (Ca), Strontium (Sr), barium (Ba) and radium (Ra) which have two electrons in their outermost shell. All these elements are also metallic in nature and are commonly known as alkaline earth metals with the exception of beryllium. Because of their low density, alkali metals and alkaline earth metals are called lighter metals. Both alkali and alkaline earth metals are highly reactive and hence do not occur in free state but found in combined state. Whereas alkali metals mostly occur as halides, oxides, silicates, borates and nitrates, alkaline earth metals mainly occur as silicates, carbonates, sulphates and phosphates. Some alkali & alkaline earth metals occur abundantly in nature. Calcium is the fifth, magnesium is the sixth, sodium is seventh and potassium is eight barium is the fourteenth and strontium is the fifteenth most abundant element by weight in the earth’s crust. Sodium and magnesium are also present in sea water brine wells and few salt lakes.

Anamolous behavour of first element

The first element of a group differs considerably from the rest of the elements of the same group. This anomolous behaviour is due to • Smaller size of their atoms • Their higher ionization energies • Their higher electronegativites

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• Absence of vacant d – orbitals in their valence shell • High polarizing power of its cation. Thus Li differes from the rest of alkali metals (Na, K, Rb & Cs) and Be differs from rest of the alkaline earth metals (Mg, Ca, Sr & Ba) Diagonal Relationships On moving diagonally some members show similar properties with the members of next higher group which is particularly seen in the elements of second and third periods of the periodic table. However the similarities shown are far less pronounced than the similarities with in a group.

The main reasons for the diagonal relationship are • Similarity in electropositive character: The electropositive character

decreases along a period, but increases down a group. Hence on moving diagonally the two opposing trend partially cancels out. As a result diagonally related elements have similar electropositive character and hence exhibit similar properties.

• Similarity in polarizing power: On moving along a period from left to right, the charge on the ions increases while ionic size decreases, hence polarizing power increases. On moving down the group, the ionic size increases and hence polarizing power decreases. On moving diagonally, these two trends partially cancel out. As a result thus diagonally related elements have same polarizing power and thus exhibit similar properties.

• Similarity in atomic or ionic radii: The atomic and ionic radii decrease across a period and increase in a group. Evidently on moving diagonally, the two trends partially cancel out. As a result, diagonally related elements have similar atomic & ionic radii and hence have similar properties.

Group I

The group I comprising Li, Na, K, Rb, Cs & Fr are commonly called alkali metals. These are called alkali metals because hydroxides of these metals are strong alkali. For example NaOH and KOH. Francium is radioactive and has a very short life (half life of 21 minutes), therefore very little is known about it.

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Physical Properties of Alkali Metals The general electronic configuration of alkali metals may be represented by [noble gas] where n = 2 to 7

*ppm (parts per million) ** percentage by weight All the alkali elements are silvery white solid.These are soft in nature and can be cut with the help of knife except the lithium. When freshly cut, they have a bright lusture which quickly fades due to surface oxidation. These are highly malleable and ductile. The silvery luster of alkali metals is due to the presence of highly mobile electrons of the metallic lattice. There being only a single electron per atom, the metallic bonding is not so strong. As the result, the metals are soft in nature. However, the softness increases with increase in atomic

Property ElementsLi Na K Rb Cs Fr

(Radioactive)

Atomic Number 3 11 19 37 55 87Electronic Configuration

2s1 3s1 4s1 5s1 6s1 7s1

Atomic Mass 6.94 22.99 39.10 85.47 13.91 223Metallic radius (pm) 152 186 227 248 265 375Ionic radius (M+/pm) 76 102 138 152 167 180Ionization enthalpy(kJ mol–1)

I 520 496 419 403 376 –II 7298 3562 3051 2633 2230 –

Electro negativity(Pauling Scale)

0.98 0.93 0.82 0.82 0.79

Density/g cm–3 (at 298K)

0.53 0.97 0.86 1.53 1.90

Melting point/K 454 371 336 312 302Boiling point/K 1615 1156 1032 961 944E°(V) at 298K forM+(aq) + e–→ M(s)

–3.04

–2.714

–2.925

–2.930

–2.927

Occurrence inAtmosphere

18* 227** 1.84** 78.12* 2.6*

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number due to continuous decrease in metallic bond strength on account of an increase in atomic size. Atomic and Ionic Radii The atoms of alkali metals have the largest size in their respective periods. The atomic radii increase on moving down the group among the alkali metals.

Reason On moving down the group a new shell is progressively added. Although, the nuclear charge also increases down the group but the effect of addition of new shells is more predominant due to increasing screening effect of inner filled shell on the valence s-electrons. Hence the atomic size increases in a group. Alkali metals change into positively charged ions by losing their valence electron. The size of cation is smaller than parent atom of alkali metals. However, within the group the ionic radii increase with increases in atomic number. The alkali metal ions get extensively hydrated in aqueous solutions. Smaller the ion more is the extent or degree of hydration. Thus, the ionic radii in aqueous solution follow the order Li+ > Na+ > K+ > Rb+ > Cs+ The charge density on Li+ is higher in comparison to other alkali metals due to which it is extensively hydrated.

Ionization Energy (Ionization enthalpy) The first ionization energy of the alkali metals are the lowest as compared to the elements in the other group. The ionization energy of alkali metals decreases down the group.

Reason The size of alkali metals is largest in their respective period. So the outermost electron experiences less force of attraction from the nucleus and hence can be easily removed. The value of ionization energy decreases down the group because the size of metal increases due to the addition of new shell along with increase in the magnitude of screening effect.

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Oxidation State The alkali metals show +1 oxidation state. The alkali metals can easily loose their valence electron and change into uni-positive ions M → M+ + e- Reason Due to low ionization energy, the alkali metals can easily lose their valence electron and gain stable noble gas configuration. But the alkali metals cannot form ions as the magnitude of second ionization energy is very high. Reducing Properties The alkali metals have low values of reduction potential (as shown in table-I) and therefore have a strong tendency to lose electrons and act as good reducing agents. The reducing character increases from sodium to caesium. However lithium is the strongest reducing agent. Reason The alkali metals have low value of ionization energy which decreases down the group and so can easily lose their valence electron and thus act as good reducing agents. Melting and Boiling Points The melting and boiling points of alkali metals are very low because the intermetallic bonds in them are quite weak. And this decreases with increase in atomic number with increases in atomic size. Density The densities of alkali metals are quite low as compared to other metals. Li, Na and K are even lighter than water. The density increases from Li to Cs.

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Reason Due to their large size, the atoms of alkali metals are less closely packed. Consequently have low density. On going down the group, both the atomic size and atomic mass increase but the increase in atomic mass compensates the bigger atomic size. As a result, the density of alkali metals increases from Li to Cs. Potassium is however lighter than sodium. It is probably due to an unusal increase in atomic size of potassium. Nature of Bond Formed All the alkali metals form ionic (electrovalent) compounds. The ionic character increases from Li to Cs because the alkali metals have low value of ionization energies which decreases down the group and hence tendency to give electron increases to form electropositive ion. Conductivity The alkali metals are good conductors of heat and electricity. This is due to the presence of loosely held valence electrons which are free to move throughout the metal structure. Photoelectric Effect

Alkali metals (except Li) exhibit photoelectric effect (A phenomenon of emission of electrons from the surface of metal when light falls on them). The ability to exhibit photoelectric effect is due to low value of ionization energy of alkali metals. Li does not emit photoelectrons due to high value of ionization energy. Flame Colouration The alkali metals and their salts impart a characteristic colour to flame

Li Na K RbColour Crimson Red Golden Yellow Pale Violet Violet Sky Bluel/nm 670.8 589.2 766.5 780.0 455.5

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On heating an alkali metal or its salt (especially chlorides due to its more volatile nature in a flame), the electrons are excited easily to higher energy levels because of absorption of energy. When these electrons return to their ground states, they emit extra energy in form of radiations which fall in the visible region thereby imparting a characteristic colour to the flame. Chemical Properties of Alkali Metals The alkali metals are highly reactive metals and the reactivity increases down the group. The reactivity is due to- • Low value of first ionization energy • Large size • Low heat of atomization Reaction with Oxygen The alkali metals tarnish in air due to the formation of an oxide or hydroxide on the surface. Alkali metals when burnt in air form different kinds of oxides. For example the alkali metals on reaction with limited quantity of oxygen form normal oxides of formula, M2O 4M + O2 → 2M2O (Where M = Li, Na, K, Rb, Cs) When heated with excess of air, lithium forms normal oxide,Li2O ; sodium forms peroxide, Na2O2, whereas potassium rubidium and caesium form superoxides having general formula MO2 4Li O2 → 2Li2O ( Lithium oxide)

2Na + O2 Na2O2 ( Sodium peroxide) K + O2 → KO2 ( Potassium Superoxide) Thus the reactivity of alkali metals with oxygen increases down the group. Further, the increasing stability of peroxide or superoxide, as the size of the metal ion increases is due to the stabilization of larger anions by larger cation through higher lattice energies. Due to small size, Li+ has a strong positive field around it which attracts the negative charge so strongly that it does not permit the oxide anion O-2 to combine with another oxygen to form peroxide ion, O2-2. On the other hand, Na+ ion because of its large size than Li+ ion has comparatively weaker positive field around it which cannot prevent O-2 ion to combine with another oxygen to form peroxide ion O2-2 . The larger K+ , Rb+ , and Cs+ ions have still weaker positive field around them which cannot prevent even peroxide O2-2 ion, to combine with another oxygen atom to form superoxide O-2 . Reaction with Hydrogen Alkali metals react with dry hydrogen at about 673K to form colourless crystalline hydrides. All the alkali metal hydrides are ionic solids with high melting points.

2M + H2 MH (M = Li, Na, K, Rb or Cs) Some important features of hydrides are

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• The stability of hydrides decrease from Li to Cs. It is because of the fact that M-H bond becomes weaker due to increase in the size of alkali metals down the group.

• These hydrides react with water to form corresponding hydroxides and hydrogen gas.

LiH + H2O → LiOH + H2 NaH + H2O → NaOH + H2 • These hydrides are strong reducing agents and their reducing nature increases

down the group. • Alkali metals also form complex hydrides such as LiAIH4 and NaBH4 which

are good reducing agents. • All these hydrides react with proton donors such as water, alcohols, gaseous

ammonia and alkynes liberating H2 gas.

NaH(S) + ROH (l) RONa (S) + H2 (g)

NaH (S) + NH3 (g) NaNH2 (S) + H2 (g)

2KH (S) + HC ≡ CH (g) KC ≡ CK (S) + 2H2 (g) • The order of reactivity of the alkali metals towards hydrogen decreases as we

move down the group from Li to Cs. This is due to the reason that the lattice energies of these hydrides decreases progressively as the size of the metal cation increases and thus the stability of these hydrides decreases from LiH to CsH.

Reaction with Water The alkali metals are known to have large negative reduction potential values. As a result they can act as better reducing agents as compared to hydrogen. Hence, alkali metals react with water and other compounds containing acidic hydrogen atoms such as hydrogen halides (HX) and acetylene (C2H2) and liberate H2 gas 2Na + H2O → 2NaOH + H2 2Na + 2HCI → 2NaCI + H2 2Na + 2HC ≡ CH → 2NaC≡ CH + H2 Sodium acetylide The reaction becomes more and more violent as we move down the group. Thus, Lithium reacts gently, sodium melts on the surface of water and the molten metal moves around vigorously and may sometimes catch fire. Potassium melts and always catches fire and so are Rb and Cs. Reaction with Halogens Alkali metals react vigorously with halogens to form metal halides of general formula MX, which are ionic crystalline solids. 2M + X2 → 2MX M = Li, Na, K, Rb or Cs and X = F, Cl, Br or I

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Reactivity of alkali metals with particular halogens increases from Li to Cs. On the other hand, reactivity of halogens decreases from F2 to I2 . Solubility in liquid Ammonia All alkali metal dissolve in liquid ammonia giving deep blue solutions which are conducting in nature. These solutions contain ammoniated cations and ammoniated electrons as shown below: M + ( x + y ) NH3 → M+ ( NH3 )x + e-(NH3)y The blue colour of the solution is considered to be due to ammoniated electrons which absorb energy corresponding to red region of the visible light for the their excitation to higher energy levels. The transmitted light is blue which imparts blue colour to the solutions. The electrical conductivity of the solution is due to both ammoniated cations and ammoniated electrons. The blue solution on standing slowly liberates hydrogen resulting in formation of amide: 2M + 2NH3 → 2MNH2 + H2 (Metal amide) At concentrations above 3M, the solutions of alkali metals in liquid ammonia are copper-bronze coloured. These solutions contains clusters of metal ions and hence possess metallic lusture. The blue coloured solutions are paramagnetic due to presence of large number of unpaired electrons, but bronze solutions are diamagnetic due to formation of electron clusters in which ammoniated electrons with opposite spin group together These solutions are stronger reducing agents than hydrogen and hence will react with water to liberate hydrogen. Reaction with Sulphur and Phosphorus Alkali metals react with sulphur and phosphorus on heating to form sulphides and phosphides respectively.

16 Na + S8 8Na2S Sodium sulphide

12Na + P4 4Na3P Sodium Phosphide Reaction with Mercury Alkali metals combine with mercury to form amalgams. The reactions is highly exothermic in nature Na + Hg → Na (Hg) Sodium amalgam Lithium is the • first memeber of alkali metals. • Atomic number of lithium is 3 while its atomic weight is 6.94 u. • Electyronc configuration of lithium is 1s2 2s1.

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Extraction of Lithium

Minerals of Lithium

• Spodumene, LiAl(SiO3)2 (6% Lithium) • Triphylite (Li, Na)2PO4 (Fe, Mn)3(PO4)2 (4% Lithium) • Petalite LiAl(Si2O5)4 (2.7 – 3.7% Lithium) • Lepidolite (Li, Na, K)2(SiO3)3(FOH)2 (1.5% Lithium) • Amblygonite LiAl(PO4)F

Difficulties Encountered During Extraction of Alkali Metals Alkali metals, can not be extracted from their ores by the usual methods of extraction of metals because of the following difficulties: • Alkali metals are strong reducing agents and hence can not be extracted by

reduction of their oxides or chlorides. • Alkali metals being highly electropositive can not be displaced from the

aqueous solutions of their salts by other metals. • Alkali metals can not be isolated by electrolysis of the aqueous solution of

their salts since hydrogen is liberated at the cathode instead of the alkali metal because the discharge potentials of alkali metals are much higher than that of the hydrogen. However, by using mercury as cathode, the alkali metals can be deposited at the cathode but the alkali metals so deposited readily combines with mercury to form an amalgam from which its recovery is very difficult.

• Therefore in view of above difficulties, only successful method is the electrolysis of their molten (fused) salts usually chlorides.

Extraction of Lithium It involves the following steps: Preparation of Lithium chloride The minerals are first of all converted into lithium chloride by any one of the following methods:

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Acid treatment method The finely powdered silicate ore is first heated to about 1373 K to make it more friable and then with H2SO4 at 523 K. The Li2SO4H2O thus formed is cooled, leached with water and then filtered to remove silica (SiO2). The filtrate thus obtained is treated with a calculated amount of Na2CO3 to precipitate aluminium and iron as carbonates which are filtered off. Excess of Na2CO3 is then added to the filtrate to precipitate Li2CO3. This is filtered and dissolved in HCl to obtain LiCl which is purified by extraction with alcohol. Fusion Method The powdered silicate mineral is fused with CaCO3 and the fused mass is extracted with HCl and filtered. The filterate contains chlorides Li, Al, Ca, Na and K whereas silicon is removed as insoluble residue. The filterate is evaporated to dryness and the residue is extracted with pyridine in which only LiCl dissolves. Pyridine is distilled off while LiCl is left behind. The method discussed above may be summed up in the following flow-sheet.

Electrolysis of Lithium Chloride A mixture of dry lithium chloride (55%) and potassium chloride (45%) is fused and electrolysed in an electrolytic cell shown in the figure.

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Potassium chloride is added to increase the conductivity of lithium chloride and to lower the fusion temperature. The cell is operated at a temperature of about 723 K and voltage of 8-9 volts is applied. As a result of electrolysis, the following reactions take place: LiCI→ Li+ + CI- At cathode: Li+ + e- → Li At anode: 2CI- - 2e- → CI2 Chlorine gas, a valuable by product liberated at the anode leaves the cell through the exit while molten lithium rises to the surface of the fused electrolytes and collects in the cast iron enclosure surrounding the cathode. The metal thus obtained is 99% pure and is preserved by keeping it wrapped in paraffin wax. It may be noted here that lithium being the lightest metal known (density = 0.534 g ) can not be stored in kerosene oil since it floats on the surface. Physical Properties of Lithium • Lithium is a silvery white metal. • It is the hardest alkali metal but still is soft enough to be cut with a knife. • Atomic and ionic radii of lithium are the lowest amongst alkali metals. • Li has highest melting point among the alkali metals.

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Chemical Properties of Lithium Lithium is highly reactive element. However, among alkali metals lithium is the least reactive.

NoteThe Ionization energy of alkali metals follows the orderLi > Na > K > Rb > CsThus the ease of releasing electron from alkali earth metals should follow the orderLi < Na < K < Rb < CsTherefore, cesium atoms should lose electrons most easily, and lithium atom should do it with difficulty. So, lithium should act as q weaker reducing agent than cesium. But, experimentally, lithium is found to be the strongest reducing agent in the group. Li acts as the strongest reducing agent dye to it low ionization energy and very large hydration energy of enthalpy.

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Lithium is the only alkali metal which combines directly with nitrogen to form lithium nitride. Lithium nitride is ionic and is ruby red. On heating it decomposes to its constituent element. It also reacts with water evolving ammonia.

2Li3N 6Li + N2

Li3N + 3H2O 3LiOH + NH3 Reaction of Lithium with Ammonia Like other alkali metals, lithium dissolves is liquid ammonia to form a deep blue solution due to formation of ammoniated electrons.

Li + ( X + Y ) NH3 Li ( NH3)x + e- (NH3)y However, when NH3 gas is passed over molten lithium. Lithium amide is formed

2Li + 2NH3 2LiNH2 + H2 Uses of Lithium

• Lithium • lead alloy (0.05% Li) which is used for making toughened bearings and sheets

for cables. • Lithium – Aluminium alloy has great tensile strength and elasticity like that of

mild steel. It is used for air craft construction. • Lithium – magnesium alloy (with 14% Li) is extremely tough and corrosion

resistant which is used for armour plate and aerospace components. • Lithium is used for refining of metal like copper and nickel as it combines

readily with oxygen and nitrogen and thus removes the last traces of oxygen and nitrogen.

• Lithium chloride is used in air conditioning plants to regulate the humidity. • Lithium aluminium hydride (LiAlH4) is used as a reducing agent in synthetic

organic chemistry

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• Lithium carbonate is used in making special variety of glass which is very strong and is weather proof.

Anomalous Behaviour of Lithium and its Diagonal Relationship with Magnesium The properties of lithium are quite different from the properties of other alkali metals. On the other hand, it shows greater resemblance with magnesium, which is diagonally opposite element of it. The main

reasons for the anomalous behaviour of lithium as compared to other alkali metals are • The extremely small size of lithium atom and its ion. • Greater polarizing power of lithium ion ( Li+), due to its small size which result

in the covalent character in its compounds. • Least electropositive character and highest ionization energy as compared to

other alkali metals. • Non availability of vacant d-orbitals in the valence shell. The reason for resemblance of properties of lithium with magnesium is that these two elements have almost same polarizing power. The following points illustrate the anomalous properties of lithium and its diagonal relationship with magnesium: • The melting point and boiling point of lithium are comparatively high. • Lithium is much harder than the other alkali metals. Magnesium is also hard

metal. • Lithium reacts with oxygen least readily to form normal oxide whereas other

alkali metals form peroxides and superoxides. • LiOH like Mg(OH)2 is weak base. Hydroxides of other alkali metals are strong

bases.

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• Due to their appreciable covalent nature, the halides and alkyls of lithum and magnesium are soluble in organic solvents.

• Unlike elements of group 1 but like magnesium. Lithium forms nitride with nitrogen. 6Li + N2 → 2Li3N

• LiCl is deliquescent and crystallizes as a hydrate, LiCI2H2O. Other alkali metals do not form hydrates. also forms hydrate, MgCI2.8H2O .

• Unlike other alkali metals lithium reacts directly with carbon to form an ionic carbide. Magnesium also forms a similar carbide.

• The carbonates, hydroxides and nitrates of lithium as well as magnesium decompose on heating.

Li2CO3 Li2O + CO2

MgCO3 MgO + CO2

2LiOH Li2O + H2O

Mg(OH)2 MgO + H2O

4LiNO3 2Li2O + 4NO2 + O2

2Mg( NO3)2 2Mg + 4NO2 +O2 • The corresponding salts of other alkali metals are stable towards heat. • Lithium nitrate, on heating, decomposes to give lithium oxide, Li2O whereas

other alkali metals nitrate decomposes to give the corresponding nitrite.

4LiNO3 2Li2O + 4NO2 + O2

2NaNO3 2NaNO2 + O2

2KNO3 2KNO2 + O2 • Li2CO3, LiOH, LiF and Li3PO4 are the only alkali metal salts which are

insoluble in water. The corresponding magnesium compounds are also insoluble in water.

• Hydrogen carbonates of both lithium and magnesium can not be isolated in solid state. Hydrogen carbonates of other alkali metals can be isolated in solid state.

Sodium is the 7th most abundant element by weight found in earth’s crust. • Atomic Number: 11 • Atomic Weight: 23 • Electronic Configuration: 1s2 2s2 sp6 3s1 • Valency : 1

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Minerals of Sodium

Extraction of Sodium

Sodium is extracted by Down’s process through electrolysis of fused sodium chloride. In this method, sodium is obtained by the electrolysis of mixture of sodium chloride (40%) and calcium chloride (60%) in fused state. The function of calcium chloride is to lower the operating temperature from 1080 K (m.pt. of NaCl) to about 850 K. The main reason for lowering the temperature are: • The melting point of sodium chloride is very high it is very difficult to

maintain it in the molten state during electrolysis. • Sodium is considerably volatile at the temperature needed for the electrolysis

and therefore, a part of the metal produced is vapourised. • Molten sodium gets dispersed in molten chloride to form a metallic fog

(colloidal solution) at high temperature. • Both sodium and chlorine, the two products of the electrolysis, have a

corrosive action on the material of the vessel employed for the electrolysis at such a high temperature.

The cell consists of a steel tank lined with fire bricks. A circular graphite anode is placed in the centre of the cell which is surrounded by a cylindrical iron cathode. The anode and cathode are separated by a steel gauge cylinder through which molten sodium chloride can pass but molten sodium cannot. The purpose of using steel gauge is to keep sodium separate from chlorine which would otherwise react with

Chile salt petre NaNO3

Glauber’s salt Na2SO4.10H2OBorax or sodium borate Na2B4O7.10H2ORock salt NaClAlbite or soda feldspar Na2O.Al2O3.6SiO2 or NaAlSi3O8

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chlorine. The anode is covered by a dome – shaped steel hood which provides the out – let for the escape of chlorine gas. The molten metal liberated at the cathode moves up and flow into the receiver containing kerosene oil. The following reactions take place: NaCl → Na++Cl- (Ionization) At Cathode: Na+ + e- → Na At anode: Cl- + Cl- → Cl2 Properties of Sodium Sodium is a soft white metal with silver – like lustre, and can also be obtained in tetragonal crystalline form. It dissolves in liquid ammonia, giving intense blue solution. The colloidal sodium in ether medium can be obtained by Svedbergls method by suspending the metal in ether and passing an oscillatory discharge from Letden jar arrangement. The colour of colloid is violet. The metal burnes in air to form Na2O and Na2O2. When heated with mercury, it forms an amulgam of varying compositions, NaHg, NaHg4 etc. In the organic qualititative work, the fusion with sodium metal is a common process. It is soluble in alcohol, forming C2H5ONa and is very much used as such. When sodium is heated with ammonia gas, sodamide is formed

2NH3 + 2Na 2NaNH2 +H2 It combines with a number of non-metals on heating 2Na + Cl2 → 2NaCl 2Na + S → 2Na2S 2Na + H2 → 2NaH With water, a violent action takes place and hydrogen gas is evolved. 2Na + 2H2O→ 2NaOH + H2 It displaces hydrogen from acids 2HCl + 2Na → 2NaCl + H2 It acts as a reducing agents because of its ease with which it can lose its valence electron.

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Al2O3 + 6Na → 2Al + 3Na2O SiO2 + 4Na → Si + 2Na2O CO2 + 4Na → 2Na2CO3 + C Uses of Sodium Following are some of the many uses of sodium metal • In the manufacturing of sodium peroxide, sodium cyanide and sodium

methoxide • As a reducing agent in the extraction of boron and silicon in the form of

sodium amalgam. • As a reagent in organic analysis. • Because of its high thermal conductivity, it is employed for filling valves of

aircraft engines. • In the production of rich yellow light by sealing it in electric bulb containing

argon or mercury vapour.

• In organic reactions such as condensation, polymerization, isomerization and preparation of metal alkyls and aryls.

Sodium Hydroxide/ Caustic Soda (NaOH)

Caustic soda is an article of great commercial importance and, therefore, is prepared on a large scale.

Electreolystic Process for perparation of NaOH This involves the electrolysis of a solution of sodium chloride. The solution contains sodium, chloride, hydrogen and hydroxide ions. In passing the current sodium and hydrogen ions move toward the cathode but hydrogen ions are able to accept the electrons more easily than sodium ions, with the result that hydrogen gas is liberated with the decomposition of more water molecules while sodium ions remain in the

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solution. At anode chloride ions give up electrons in preference to hydroxide ions and thus chlorine gas is liberated there.

The solution on electrolysis , therefore , becomes richer in sodium hydroxide

When calcium hydroxide is added to sodium carbonate solution, calcium carbonate is precipitated, leaving sodium hydroxide in solution Na2CO3 + Ca(OH)2 → CaCO3 ¯ + 2NaOH Properties NaOH is stable towards heat but is reduced to metal when heated with carbon 2NaOH + 2C → 2Na +2CO + H2 FeCl3 + 3NaOH → Fe(OH)3 + 3NaCl NH4Cl + NaOH → NaCl + NH3 (pungent smell) + H2O HgCl2 + 2NaOH → HgO (yellow powder) + 2NaCl + H2O Zn(OH)2 ¯ + 2NaOH → Na2ZnO2 + 2H2O Al2O3 ¯ + 2NaOH → 2NaAlO2 + H2O SiO2 + 2NaOH→ Na2SiO3 + H2O 3P + 3 NaOH +3H2O→ PH3 + 3NaH2PO2 2Al + 2 NaOH + 2H2O → 3H2 + 2NaAlO2

General Characteristic of the Compounds of the Alkali Metals

At Anode At cathode Overall reaction2H2O + 2e → H2 + OH-

2Cl- → Cl2 + 2e

2Na++Cl-+H2O → 2Na++OH- +H2 +Cl2

Table of Content• Oxides and Hydroxides

◦ Basic Strength◦ Solubility and Stability◦ Formation of Salts with Acids

• Halides of Alkali Metals◦ Polarization Effects◦ Lattice Energies

• Hydration Energy• Salts of Oxoacids• Some other Compounds of Alkali Metals

◦ Sodium Bicarbonate◦ Potassium Bicarbonate◦ Sodium Chloride◦ Potassium Chloride◦ Sodium Sulphate◦ Potassium Sulphate

• Related Resources

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Oxides and Hydroxides All the alkali metals, their oxides, peroxides and superoxides readily dissolve in water to produce corresponding hydroxides which are strong alkalies eg • 2Na + 2H2O → 2NaOH + H2 • Na2O + 2H2O → 2NaOH • Na2O2 + 2H2O → 2NaOH + H2O2 • 2KO2 + 2H2O → 2KOH + H2O2 + O2 Thus peroxides and superoxides also act as oxidizing agents since they react with H2O forming H2O2 and O2 respectively. The hydroxides of all the alkali metals are white crystalline solids. They are strongest of all base and readily dissolve in water with the evolution of much heat. • The basic strength of these hydroxides increases as we move down the group

Li to Cs. • The hydroxides of alkali metals behave as strong bases due to their low

ionization energies which decrease down the group. • The decrease in ionization energies leads to weakening of the bond between

metal and hydroxide ion and M – O bond in M – O – H can easily break giving M+ and OH- .

• This results in the increased concentration of hydroxyl ions in the solution i.e increased basic characters.

Solubility and Stability All these hydroxides are highly soluble in water and thermally stable except lithium hydroxide. 2LiOH +Δ → Li2O + H2O Formation of Salts with Acids Alkali metals hydroxides being strongly basic react with all acids forming salts. • NaOH + HCI → NaCI + H2O • 2NaOH + H2SO4 → Na2SO4 + 2H2O

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Halides of Alkali Metals The alkali metals combine directly with halogens under appropriate conditions forming halides of general formula MX. These halides can also be prepared by the action of aqueous halogen acids (HX) on metals oxides, hydroxides or carbonate. • M2O + 2HX → 2MX + H2O • MOH + HX → MX + H2O • M2CO3 + 2HX → 2MX + CO2 + H2O (M = Li, Na, K, Rb or Cs) • (X = F, Cl, Br or I) All these halides are colourless, high melting crystalline solids having high negative enthalpies of formation.

The value decreases in the order: Fluoride > Chloride > bromides > Iodide Thus fluorides are the most stable while iodides are the least stable. The trends in melting points, boiling points and solubility of alkali metals halides can be understood in terms of polarization effects, lattice energy and hydration of ions.

Solved ExamplesQuestions:Name the alkali metal which forms superoxides when heated in excess of air and why?Solution:Potassium forms superoxides when heated in excess of air. This is due to the stabilization of large size cation by large size anion.K + O2 → KO2 (potassium superoxide)___________________________________________________Questions:Why lithium forms only lithium oxide and not peroxide or super oxides?Solution:Due to the small size of lithium, it has a strong positive field around it. On combination with the oxide anion (O2–), the positive field of lithium ion restricts the spread of negative charge towards another oxygen atom and thus prevents the formation of higher oxides.

Standard enthalpies of formation in (kJ/mol-1)Element MF MCl MBr MILi -612 -398 -350 -271Na -569 -400 -360 -288K -563 -428 -392 -328Rb -549 -423 -389 -329Cs -531 -424 -395 -337

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Polarization Effects

Comparison of ionic and covalent character of alkali metal halides. When a cation approaches an anion, the electron cloud of the anion is attracted towards the cation and hence gets distorted. This effect is called polarization. The power of the cation to polarize the anion is called its polarizing power and the tendency of the anion to get polarized is called its polarizability. The greater the polarization produced more is the concentration of the electrons between the two atoms thereby decreasing the ionic character or increasing the covalent character. The covalent character of any compound in general depends upon the following factors.

• Size of the Cations Smaller the cation greater is its polarizing power and hence larger is the covalent character. The covalent character decreases as size of cation increases. LiCl > NaCl > KCl > RbCl > CsCl Thus LiCl is more covalent than KCl. • Size of the Anion Larger the anion, greater is its polarizability. This explains the covalent character of lithium halides is in order LiI > LiBr > LiCl > LiF • Charge of the Ion Greater the charge on the cation greater is its polarizing power and hence larger is the covalent character. The covalent character of some halides increase in the order Na+Cl- < Mg+2Cl2 < Al+3 Cl3 Similarly greater the charge on the anion, more easily it gets polarized thereby imparting more covalent character to the compound formed eg covalent character increase in the order NaCI < Na2SO4 < Na3PO4 Thus the covalent character decreases as the charge of the anion decrease.

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• Electronic configuration of the Cation If two cations have the same charge and size, the one with pseudo noble gas configuration i.e. having 18 electrons in the outermost shell has greater polarizing

power than a cation with noble gas configuration i.e having 8 electrons. For example CuCl is more covalent than NaCl. Lattice Energies Lattice energy is defined as the amount of energy required to separate one mole of solid ionic compound into its gaseous ions. Evidently greater the lattice energy, higher is the melting point of the alkali metals halide and lower is its solubility in water

Hydration Energy It is the amount of energy released when one mole of gaseous ions combine with water to form hydrated ions. • M+ (g) + aq → M+ (aq) + hydration energy • X- (g) + aq → X- (aq) + hydration energy • Higher the hydration energy of the ions greater is the solubility of the

compound in water. • Further the extent of hydration depends upon the size of the ions. Smaller the

size of the ion, more highly it is hydrated and hence greater is its hydrated ionic radius and less is its ionic mobility (Conductance).

• From above arguments, the melting point and solubility in water or organic solvent of alkali metal halides can be explained

Compound

Lattice energy

Hydration* energy

Solubility

Melting point

LiCl -845 -876 63.7 887NaCl -770 -776 35.7 1084KCl -703 -700 34.7 1039RbCl -674 -680 77.0 988CsCl -644 -646 162 925NaF -893 -919 4.22 1261NaCl -770 -776 35.7 1028NaBr -730 -745 116 1084NaI -685 -685 184 944LiF -1005 -1019 0.27 1115CsI -582 -670 44.0 1115

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• A delicate balance between lattice enthalpy and hydration enthalpy determines the ultimate solubility of a compound in water. For eg. Low solubility of LiF (0.27 g/100 g H2O ) is due to its high lattice energy ( - 1005 KJmol-1) whereas the low solubility of CsI (44g/100g H2O ) is due to smaller hydration energy of the two ions (-670 KJ/mol) . The solubility of the most of alkali metal halides except those of fluorides decreases on descending the group since the decrease in hydration energy is more than the corresponding decrease in the lattice energy.

• Due to small size and high electronegativity, lithium halides except LiF are predominatantly covalent and hence are soluble in covalent solvents such as alcohol, acetone, ethyl acetate, LiCl is also soluble in pyridine. In contrast NaCl being ionic is insoluble in organic solvents.

• Due to high hydration energy of Li+ ion, Lithium halides are soluble in water except LiF which is sparingly soluble due to its high lattice energy.

• For the same alkali metal the melting point decreases in the order fluoride > chloride > bromide > iodide because for the same alkali metal ion, the lattice energies decreases as the size of the halide ion increases.

• For the same halide ion, the melting point of lithium halides are lower than those of the corresponding sodium halides and thereafter they decrease as we move down the group from Na to Cs.

• The low melting point of LiCl (887 K) as compared to NaCl is probably because LiCl is covalent in nature and NaCl is ionic.

Salts of Oxoacids Since the alkali metals are highly electropositive, therefore their hydroxides are very strong bases and hence they form salts with all oxoacids ( H2CO3, H3PO4, H2SO4, HNO3, HNO2 etc) . They are generally soluble in water and stable towards heat. The carbonates (M2CO3) of alkali metals are remarkably stable upto 1273 K, above which they first melt and then eventually decompose to form oxides. Li2CO3 , however is considerably less stable and decomposes readily. Li2CO3 + Δ→ Li2O + CO2 This is presumably due to large size difference between Li+ and CO2-3 which makes the crystal lattice unstable. Being strongly basic, alkali metals also form solid bicarbonates. No other metals forms solid bicarbonates though NH4HCO3 bicarbonate though it does exist in solution. All of them also exists as a solid. Lithium, however does not form solid

Solved ExampleQuestion:Why are alkali metal halides soluble in water?Solution:Alkali metal halides are soluble in water due to their high ionic character and low lattice energy.

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2MHCO3 → M2CO3 + CO2 + H2O All the carbonates and bicarbonates are soluble in water and their solubilities increase rapidly on descending the group. This is due to the reason that lattice energies decrease more rapidly than their hydration energies on moving down the group.

Some other Compounds of Alkali Metals Sodium Bicarbonate A concentrated solution of sodium carbonate absorbs CO2 to give sparingly soluble sodium bicarbonate. Na2CO3 + CO2 + H2O → 2NaHCO3 Properties of sodium bicarbonates • It is sparingly soluble in water • When heated between 250°C and 300°C, it is converted into pure anhydrous

sodium carbonate which can be used for standardising acids. 2NaHCO3 → Na2CO3 + H2O + CO2

Potassium Bicarbonate It is made by absorbing CO2 in moist potassium carbonate and then drying the product in a porous plate. K2CO3 + H2O + CO2 → 2KHCO3 Properties of potassium bicarbonates KHCO3 resembles NaHCO3, but is much more soluble in water. The solution is strongly alkaline owing to hydrolysis. KHCO3 + H2O → KOH + H2CO3 Sodium Chloride (NaCl) It is also called common salt occurs abundantly in nature as rock salt or halite. The most abundant source is sea-water where sodium chloride occurs to the extent of 2.6 – 2.9 percent. The sea water is exposed to the sun and air in large shallow pits. The gradual evaporation of water leading to the crystallization of the salt. The purification is done by dissolving the salt in minimum volume of water and filtering, if necessary, to remove insoluble impurities. The solution is then saturated with a current of dry hydrogen chloride whereby crystals of pure sodium chloride separate out.

Solved ExampleQuestion:Complete and balance the following: LiNO3 +Heat → NaNO3 +Heat → Solution:4LiNO3 → 2Li2O + 4NO2 + O2 2NaNO3 → 2NaNO2 + O2

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Properties of sodium chloride • NaCl is a colourless crystalline salt, almost insoluble in alcohol and highly

soluble in water. • It gives rise to HCl when heated with conc. H2SO4 and Cl2, with MnO2 plus

H2SO4. NaCl + H2SO4 → NaHSO4 + HCl ↑ NaHSO4 + NaCl →Na2SO4 + HCl ↑ 2NaCl + MnO2 + 2H2SO4 → MnSO4 + Na2SO4+ 2H2O + Cl2 ↑ Potassium Chloride KCl is prepared from fused carnallite – nearly pure KCl separates from the melt, leaving fused MgCl2 behind. KCl, MgCl2×6H2O → KCl + MgCl2×6H2O Properties of potassium chloride It is colourless cubic crystal like solid soluble in water. Its solubility increases almost linearly with temperature. Sodium Sulphate, Na2SO4 The anhydrous salt known as salt cake, is prepared on an industrial scale by heating strongly sodium chloride with conc. sulphuric acid. NaCl + H2SO4 → NaHSO4+ HCl ↑ NaCl + NaHSO4 → Na2SO4 + HCl ↑ Glauber’s salt or hydrated sodium sulphate, Na2SO4×10H2O is prepared from salt cake by crystallisation from water below 32°C This temperature represents the transition temperature for Na2SO4 and Na2SO4.10H2O. It is colourless salt, crystallising in large monoclinic prisms. It is exceedingly soluble in water. Potassium Sulphate, K2SO4 It is obtained by strongly heating potassium chloride with conc. H2SO4 KCl + H2SO4 → KHSO4 + HCl KCl + KHSO4 → K2SO4+ HCl

It is colourless crystalline salt, m.p. 1070°C. It is less soluble in water than sodium sulphate and has no hydrate like the later.

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Alkaline Earth Metals

The group 2 of the periodic table consists of six metallic elements. They are Beryllium (Be), Magnesium (Mg), Calcium (Ca), Strontium (Sr), Barium (Ba) and Radium (Ra). The name alkaline earth metals was given to magnesium, calcium, barium & strontium since their oxides were alkaline in nature and these oxide remained unaffected by heat or fire and existed in earth.

So, group 2 metals are called alkali earth metals because their hydroxides are strong alkali (just like those of alkali metals) plus these all are found in earth crust. Occurrence of Alkali Earth Metals

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Like alkali metals, alkaline earth metals are also highly reactive and hence do not occur in the free state but are likely distributed in nature in the combined state as silicates, carbonates, sulphates and phosphates.

Group IIA (Alkaline earth metals) and groups IIB (Zn, Cd, Hg) Mg acts as a bridge element between IIA and IIB.

Elements

Abundance

Main Minerals Uses

Beryllium

2.8 to 10-3%

First detected in 1798 in the gemstone beryl and emerald (Be3Al2Si6O1)

Used in corrosion resistant alloys.

Magnesium

2.33%,

7th most abundant element in earth’s crust

Pure Mg first prepared in 1800, named after the magnesia district in Thessaly Greece where large deposits of the mineral are found

When alloyed with Al, Mg is widely used as structural materials because of its high strength, low density and ease in machining.

Calcium

4.15%, 5thmost abundant element in earth’s crust.

CaCO3.2H2O obtained in pure form in 1808, calcium is derived from latin word calx, meaning “lime”

As an alloying agent for hardness in aluminium compounds. Calcium is the primary constituent of teeth and bones.

Strontium

0.038% Discovered in 1787 and named after the small town of strontion (Scotland)

SrCO3 is used for the manufacture of glass for colour TV picture tubes.

Barium 0.042% Found in minerals witherite (BaCO3) and barite (BaSO4) after which it is named.

BaSO4 is used in medicine as a contrast medium for stomach and intestine

X – raysRadium

Traces Isolated as chloride in 1898 from the mineral pitchblende

Used in cancer radiotheraphy

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S.No.

Properties

IIA(Be, Mg, Ca, Sr, Ba, Ra) IIB (Zn, Cd, Hg)

1 Electronic configuration

[Inert gas] ns2 [Inert gas] (n – 1)d10ns2

2 Block S – block d – block3 Oxidati

on state

+2 +2, mercury also forms dimeric Hg2+2

4 Nature of oxide

BeO is amphoteric, other oxides are basic.

ZnO is amphoteric, CdO and MgO are basic

5 Nature of Halides

Electron – deficient BeX2, others (MX2) are ionic:

MgCl2 < CaCl2 < SrCl2 < BaCl2

ZnCl2, CdCl2 are ionic but less than IIA, HgCl2 is covalent.

6 Nature of sulphates

Less soluble in water and solubility decreases down the group BeSO4 > MgSO4 > CaSO4 > SrSO4 > BaSO4

More soluble than IIA

7 Nature of hydroxides

Solubility of hydroxides increases as we move down the group.

Solubility of hydroxides decrease as we move down the group.

8 Nature of sulphides

Soluble ZnS, CdS, HgS insoluble and precipitate in salt analysis.

9 Reactivity

Increases as we move down the group Be < Mg < Ca < Sr < Ba

Decreases as we move down the group Zn > Cd > Hg

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Electronic Configuration

The general electronic configuration of alkaline earth metals is ns2.

Physical Properties of Group II elements

Atomic and Ionic Radii The atomic radii as well as ionic radii of the members of the family are smaller than the corresponding members of alkali metals.

Ionization Energy The alkaline earth metals owing to their large size of atoms have fairly low values of ionization energies as compared to the p – block elements. However with in the group, the ionization energy decreases as the atomic number increases. It is because of increase in atomic size due to addition of new shells and increase in the magnitude of screening effect of the electrons in inner shells. Because their (IE)1 is larger than that of their alkali metal neighbours, the group IIA metals trend to the some what less reactive than alkali metals.

The general reactivity trend is Ba > Sr > Ca > Mg > Be.

Elements Electronic ConfigurationBe 1s22s2

Mg 1s22s2sp63s2

Ca 1s22s22p63s23p64s2

Sr [Kr]5s2

Ba [Xe]6s2

Ra [Rn]7s2

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Oxidation State The alkaline earth metal have two electrons in their valence shell and by losing these electrons, these atoms acquire the stable noble gas configuration. Thus, unlike alkali metals, the alkaline earth metals exhibit +2 oxidation state in their compounds.

M → M+2 + 2e- [noble gas] Density of Alkali Earth Metals Atomic weight increases from Be to Ba in a group and volume also increases, but increase in atomic weight is more as compare to atomic volume. Therefore the density increases from Be to Ba.

Exception: Density of Mg is more as compare to that of Ca.

Order: Ca < Mg < Be < Sr < Ba

Melting and Boiling Points

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The alkaline earth metals have higher melting and boiling points as compared to those of alkali metals which is attributed to their small size and more close packed crystal lattice as compared to alkali metals and presence of two valence electrons.

Heat of Hydration The heats of hydration of M2+ decreases with an increase in their ionic size and their values are greater than that of alkali metal ions.

Alkaline earth metal ions, because of their larger charge to size ratio, exert a much stronger electrostatic attraction on the oxygen of water molecule surrounding them.

Since the alkaline earth metals (except Be) tend to lose their valence electrons readily, they act as strong reducing agents as indicated by E0 red values. The particularly less negative value for Be arises from the large hydration energy associated with the small size of Be2+ and the relatively large value of heat of sublimation.

Solubility Basic nature of oxides increases down the group but solubilities of sulphates and carbonates decrease as ionic size increases.

The solubility of most salts decreases with increased atomic weight, though usual trend is reversed with fluorides and hydroxides in this group.

Property ElementsBe Mg Ca Sr Ba Ra

Atomic number 4 12 20 38 56 88Atomic mass 9.01 24.31 40.08 87.62 137.33 226.03

Metallic radius/pm 112 160 197 215 222 -Ionic radius/pm 51 72 100 118 135 148Ionization

enthalpy (kJ mol-1)

I 899 737 590 549 503 509II 1757 1450 1146 1064 965 979

Enthalpy of hydration of M2+ ions (kJ mol-1)

-2494 -1921 -1577 -1443 -1305 -

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* ppm (parts per million) ** Percentage by weight Reactivity and Electrode potential All the alkaline earth metals are highly reactive elements since they have a strong tendency to lose the two valences s-electrons to form the corresponding dipositive ions having inert gas configuration. The high reactivity arises due to their low ionization energies and high negative values of their standard electrode potentials. Further, the chemical reactivity of alkaline earth metals increase on moving down the group because the I.E. decreases and electrode potentials become more and more negative with increasing atomic number from Be to Ra. Thus, beryllium is the least reactive while Ba (or Ra) is the most reactive element. Further since the ionization energies of alkaline earth metals are higher and their electrode potential is less negative than the corresponding alkali metals. They are less reactive than corresponding alkali metals.

Reducing Character The alkaline earth metals are weaker reducing agents than the alkali metals. Like alkali metals, their reducing character also increases down the group. This is due to the reason that the alkaline earth metals have greater tendency to lose electrons so, they act as reducing agent but since their I.E. are higher and their electrode potentials

Electronegativity

(Pauling Scale)

1.57 1.31 1.00 0.95 0.89 0.9

Density/g mol- at 298 K

1.85 1.74 1.55 2.63 3.62 5.5

Melting Point/K 1562 924 1124 1062 1002 973Boiling point /K 2745 1363 1767 1655 2078 (1973)

(uncertain)

E°(V) at 298 K for

M2+(aq) + 2e- → M(s)

-1.97 -2.37 -2.87 -2.89 -2.90 -2.92

Occurrence in Lithosphere

2* 2.76** 4.6** 384* 390* 10-10**

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are less negative than the corresponding alkali metals, therefore alkaline earth metals are weaker reducing agents than alkali metals. The sulphates are stable to heat whereas the carbonates decompose to give MO and CO2, the temperature of decomposition increasing from Mg to Ba. BeCO3 is kept in the atmosphere of CO2 to prevent its decomposition.

Flame Test Ba and Mg do not impart any colour to the fame i.e. they do not give flame test. This is due to their very small size. Ca, Sr and Ba impart brick red, Blood red and Apple green colours respectively to the flame.

Solved Examples Question 1:

The alkaline earth metals shows +2 oxidation state i.e. they always form divalent cations (M2+). Explain.

Solution:

If ionization energy were the only factor involved, than group II elements should have formed monovalent ions i.e. Mg+, Ca+ etc rather than Mg2+, Ca+2 etc.

1. This can be explained as follows:

2. The divalent cations of alkaline earth metals acquires stable inert gas configuration.

3. The divalent cations results in stronger lattices then monovalent cations and hence a lot of energy called lattice energy released during formation of divalent cations than monovalent cation which compensates the high second ionization energy.

BeCO3 MgCO3 CaCO3 SrCO3 BaCO3

<100°C 540°C 900°C 1290°C 1360°C

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4. The existence of divalent ions in the aqueous solution is due to greater hydration of the divalent ions which counter balance the high value of second ionization energy.

Question 2:

The 2nd ionization energies of the elements of group I are higher than those of the elements of group II. Explain.

Solution:

The 2nd electron in case of alkali metal is to be removed form a cation (unipostive ion) which has already acquired a noble gas configuration whereas in case of alkaline earth metals, the second electron is to be removes fro a cation which is yet to acquire the stable noble gas configuration therefore, removal of 2nd electron in case of alkaline earth metals requires much less energy than that in case of alkali metals.

There is sharp increase in third ionization energy due to stable inert gas configuration of m+2 ions. This explains the upper limit of +2 oxidation state for the elements.

Difference between Alkaline Earth Metals and Alkali Metals

Both alkaline earth metals and alkali metals are s – block elements as the last electron enters the ns – orbital. They resemble with each other in some respects but still there are certain dissimilarities in their properties on account of different number of electrons in the valency shell, smaller atomic radii, high ionization potential, higher electro negativity etc.

Properties

Alkaline earth metals Alkali metals

1 Electronic configuration

Two electrons are present in the valency shall. The configuration is ns2 (bivalent)

One electron is present in the valency shell. The configuration is ns1 (monovalent) more electropositive

2 Valency Bivalent Monovalent3 Electropo

sitive nature

Less electropositive More electropositive

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Chemical Properties of Alkali Earth Metals

Reaction With Hydrogen – (Formation of Hydrides) All the alkaline earth metals except be combine with hydrogen directly on heating to form metal hydrides of formula MH2.

M + H2 MH2

The hydride of beryllium can also be obtained by the reduction of BeCl2 with LiAlH4

4 Hydroxides

Weak bases, less soluble and decompose on heating.

Strong bases, highly soluble and stable towards heat.

5 Bicarbonates

These are not known in free state. Exist only in solution.

These are known in solid state.

6 Carbonates

Insoluble in water. Decompose on heating.

Soluble in water. Do not decompose on heating (LiCO3 is an exception)

7 Action of nitrogen

Directly combine with nitrogen and form nitrides

Do not directly combine with nitrogen except lithium

8 Action of carbon

Directly combine with carbon and form carbides

Do not directly combine with carbon

9 Nitrates Decompose on heating evolving a mixture of NO2 and oxygen

Decompose on heating evolving only oxygen

10 Solubility of salts

Sulphates, phosphates fluorides, chromates, oxalates etc are insoluble in water

Sulphates, phosphates, fluorides, chromates, oxides etc are soluble in water.

11 Physical properties

Comparatively harder. High melting points. Diamagnetic.

Soft, low melting points paramagnetic.

12 Hydration of compounds

The compounds are extensively hydrated. MgCl2.6H2O, CaCl2.6H2O, BaCl2.2H2O are hydrated chlorides.

The compounds are less hydrated. NaCl, KCl, RbCl form non – hydrated chlorides

13 Reducing power

Weaker as ionization potential values are high and oxidation potential values are low.

Stronger as ionization potential values are low and oxidation potential values are high.

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2BeCl2 + LiAlH4 → 2BeH2 + LiCl + AlCl3

Both BeH2 and MgH2 are covalent compounds having polymeric structures in which H – atoms between beryllium atoms are held together by three centre – two electron (3C - 2e) bonds as shown below:

The hydrides of other elements of this group i.e. CaH2, SrH2 and BaH2 are ionic and contain the H- ions.

All the hydrides of alkaline earth metals reacts with water liberating H2 gas and thus act as reducing agents.

MH2 + 2H2O → M (OH)2 + 2H2

CaH2 is called Hydrolith and is used for production of H2 by action of water on it.

Reaction With Carbon – (Formation of Carbides) When BeO is heated with carbon at 2175 – 2275 K a brick red coloured carbide of the formula Be2C is formed

2BeO + 2C Be2C + 2CO.

It is a covalent compound and react water forming methane.

Be2C + 4H2O → 2Be (OH)2 + CH4

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The rest of the alkaline earth metals (Mg, Ca, Sr & Ba) form carbides of the general formula, MC2 either when the metal is heated with carbon in an electric furnace or when their oxides are heated with carbon.

Ca + 2C CaC2

CaO + 3C CaC2 + CO

All these carbides react with water producing acetylene gas.

CaC2 + 2H2O → HC ≡ CH + Ca (OH)2

Reaction with Halogens The alkaline earth metals react with halogens at elevated temperature to form the halides of the types MX2.

Action of Acids

The alkaline earth metals readily react with acids liberating hydrogen.

M + 2HCl → MCl2 + H2 ( M = Be, Mg, Ca, Sr, Ba) Reaction with Ammonia Like alkali metal, the alkaline earth metals dissolve in liquid ammonia to give deep blue black solution from which ammoniates [ M (NH3)6 ]2+ can be recovered.

Solved ProblemQuestion

How does the basicity of oxides of group 2 increases down the group?

Solution:

The basicity increases down the group

BeO < MgO < CaO < SrO < BaO

amphoteric strongly - basic

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Formation of Peroxides Since larger cations stabilize larger anions. Therefore, tendency to form peroxide increases as the size of the metal ion becomes larger. Thus BaO2 is formed by passing air over heated BaO at 773K.

2BaO + O2 2BaO2

2SrO + O2 2SrO2 SrO2 is prepared in similar way but under high pressure and temperature. CaO2 is not formed this way but can be prepared as the hydrate by treating Ca (OH)2 with H2O2and then dehydrating the product.

Ca(OH)2 + H2O2 → CaO2.2H2O

Crude MgO2 has been made using H2O2 but peroxide of beryllium is not known.

All peroxide are white crystalline ionic solids containing the peroxide ion O2-2. Treatment of peroxide with acids liberates H2O2.

BaO2 + 2HCI → BaCI2 + H2O2

Reaction With Water (Formation of Hydroxides)

The electrode potential of Be (Be2+/Be = -1.97 V) is least negative amongst all the alkaline earth metals. This means that Be is much less electropositive than other alkaline earth metals and hence does not react with water or steam even at red heat.

The electrode potential of Mg (Mg+2/Mg = -2.37 V), although more negative than that of Be yet is still less negative than those of alkali metals and hence it does not react with cold water but reacts with boiling water or steam.

Mg + H2O → MgO + H2 or, Mg + 2H2O → Mg (OH)2 + H2

Mg, infact, forms a protective layer of oxide on its surface, therefore, despite its favourable electrode potential it does not react readily with water unless the oxide layer is removed by amalgamating it with mercury. In the formation of oxide film, Mg resembles Al.

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Ca, Sr and Ba have more negative electrode potentials similar to those of the corresponding group I alkali metals and hence react with even with cold water, liberating H2 and forming the corresponding metal hydroxides.

Ca + 2H2O → Ca(OH)2 + H2 Reactivity of alkaline earth metals increases as we move down the group. However, the reaction of alkaline earth metals is less vigorous as compared to alkali metals.

Reaction With Air (Nitrogen and Oxygen)

Formation of oxides and nitrides

Be metal is relatively unreactive in the massive form and hence does not react below 873K. However, powdered Be is more reactive and burns brilliantly on ignition to give a mixture of BeO & Be3N2.

2Be + O2 (air) M + H2 MH2 2BeO

3Be + N2 (air) M + H2 MH2 Be3N2 magnesium is more electropositive than Be and hence burns with dazzling brilliance in air to form a mixture of MgO and magnesium nitride.

Mg + air M + H2 MH2 MgO + Ng3N2 Ca, Sr and Ba being even more electropositive react with air readily to form a mixture of their respective oxides and nitrides.

The reactivity towards oxygen increases as we go down the group. Thus Ca, Ba and Sr are stored in paraffin but Be and Mg are not because they form protective oxide layer on their surface.

Formation of Nitrides

All alkaline earth metals are competent to producing their appropriate nitrides in reaction with nitrogen with a required vast amount of heat. The basic structure of reactions with an alkaline earth metal and nitrogen are as follows:

3 M(s) + N2 (g)Δ M3N2 (s)

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(M = Be, Mg, Ca, Sr, or Ba)

Nitrides of the alkaline earth metals are ionic and solid in nature except for beryllium nitride ( ' ), which is covalent and unpredictable. Decompositions of the alkaline earth metal nitrides occur upon heating:


Nitrides of alkaline earth metals may also react with water producing ammonia:

Nitrides of alkaline earth metals may also react with water producing ammonia:

M3N2 (s) + 6H2O (l) → 3M(OH)2 (aq) + 2NH3 (g)


Be3N2

M3N2 (s)Δ 3 M(s) + N2(g)

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S BLOCK ELEMENTS MCQ

Q1) Calcium carbide and nitrogen react to produce [ AFMC 1998] a) Calcium acetate b) calcium carbonate c) calcium Cyan ate d) Calcium Cyan amide CaC2 + N2 → CaCN2 at 1100° C Answer: (d) Q2) The salt which produces blue colour i borax bead test is .. [ AFMC 1998] a) CaCl2 b) MnSO4 c) MgCO3 d) CoCl2 ANS Co2+ produces blue colour in borax bead test Answer: (d) Q3) Tartar emetic is . . [ AFMC 2001] a) Sodium Potassium tartarate b) Tartaric acid c) Potassium antimony tartarate d) Potassium acid tartrate ANS Answer:(c) Q4) Which of the following has highest hydration energy? [ AFMC 2009] a) MgCl2 b) CaCl2 c) BaCl2 d) SrCl2 ANS The hydration energy of M2+ ion decreases with increase in ionic radii And in group ionic radius increases as go down the group. Mg+2 have lowest ionic radii hence higher hydration energy Answer: (a) Q5) Beryllium shows diagonal relationship with aluminum. Which of the following similarity is incorrect [ AFMC 2011] a) Be forms beryllates and Al forms aluminates b) Be(OH)2 Alike Al(OH)2 is basic c) Be like Al is rendered passive by HNO3 d) Be2C like Al4C3 yields methane on hydrolysis ANS

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Be(OH)2 Alike Al(OH)2 are amphoteric in nature Answer: (b) Q6) Which of the following decomposes more readily? a) Li2CO3 b) Na2CO3 c) Cs2CO3 d) K2CO3 ANS Li2CO3 is least stable carbonate. It is because Li cation is very small , has the strong polarizing action on large size anion, during decomposition results in gain in lattice energy which makes the Li2CO3less stable Answer: (a) Q7) The product obtained on fusion of BaSO4 and Na2CO3 is: [ AFMC 2005] a) BaCO3 b) BaO c) Ba(OH)2 d) BaHSO4 ANS BaSO4 + Na2CO3 → BaCO3 + Na2 SO4 Answer:(a) Q8) Which of the following is used to produce smoke screens? [ AFMC 2005] a) Calcium phospANS b) zinc sulpANS c) sodium carbonate d) zinc phospANS ANS Answer: (a) Q9) Li has the maximum value of ionization potential among the alkali metals i.e. lithium has the minimum tendency to ionize to give Li+ ion. Thus, in aq. solution lithium is .. [ AFMC 2011] a) strong reducing agent b) Poorest reduction agent c) Strongest Oxidizing agent d) Poorest oxidizing agent ANS The ionisation potential value of lithium is maximum among alkali metals i.e. its tendency to ionize to give Li+ ions should be the minimum i.e. Li should be the poorest reducing agent. But lithium is the strongest reducing agent in aq.solution due to largest value of hydration energy. Answer: (a) Q10) Among the alkali metals, cesium is the most reactive because .. [ AFMC 2008] a) its incomplete shell is nearest to the nucleus b) it has a single electron in the valance shell

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c) it is the heaviest alkali metal d) the outermost electron is more loosely bound than the outermost electron of other alkali metals. ANS Because of large size electron is more loosely bonded. hence it is most reactive in alkali metals Answer: (d) Q11) Calcium Carbide reacts with water to produce ..[ AFMC 2006] a) ethane b) methane c) ethylene d) acetylene ANS Answer:(d) Q12) Glauber salt is a) MgSO4.7H2O. b) CuSO4.5H2O. c) FeSO4.7H2O. d) Na2SO4.10H2O. ANS Answer: (d) Q13) A major constituent of Portland cement ( except lime ) is [ CPMT 1980] a) Silica b) Aluminia c) Iron oxide d) Magnesia ANS Answer: (a) Q14) Calcium cyanamide on treatment with steam under pressure gives NH3 and .. [CPMT 1986] a) Calcium carbonate b) Calcium hydroxide c) Calcium oxide d) Calcium bicarbonate ANS CaNCN + 3H2O → CaCO3 + 2NH3 Answer: (a) Q15) Which of the following is least soluble in water? [ Pb. CET 1988] a) BeSO4 b) BaSO4 c) CaSO4 d) SrSO4 ANS

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Answer:(b) Q16) Dolomite has the composition ..[Pb CET 1989] a) Kcl . MgCl2 . 6H2O b) Na3AlF6 c) CaCO3 . MgCO3 d) CaCl2 . MgCl2 . 6H2O ANS Answer: (c) Q17) Which of the following metal carbonates decomposes on heating? [ MLNR 1985] a) MgCO3 b) Na2CO3 c) K2CO3 d) Rb2CO3 ANS Answer: (a) Q18) Magnesium keeps burning in .. [ AFMC 1987] a) N2 b) CO2 c) NO2 d) N2 as well as CO2 ANS When Mg is heated 3Mg + N2 → Mg3N2 2Mg + CO2 → MgO + C Answer: (d) Q19) Drying agent which reacts with CO2 and removes water vapour is ..[AFMC 1988] a) CaO b) CaCl2 c) CaCO3 d) Ca(NO3)2 ANS Answer:(a) Q20) Thermal stability of alkaline earth metal carbonates decreases in order ..[ NCERT 1983] a) BaCO3 > SrCO3 > CaCO3 > MgCO3 b) BaCO3 > SrCO3 > MgCO3 > CaCO3 c) CaCO3 > SrCO3 > MGCO3 > BaCO3 d) MgCO3 > CaCO3 > SrCO3 > BaCO3 ANS Thermal stability decreases as the basic character of the metal hydroxide decreases Answer: (a)

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Q21) the hydration energy of Mg2+ ions is larger than that of .. a) Al3+ b) Na+ c) Be2+ d) Mg3+ ANS Na+ ion has larger size than Mg2+ ion and hence hydration energy of Mg2+ is larger than that of Na+ Answer: (b) Q22) of the following the commonly used in a laboratory desiccators is ..[MP PMT 1987] a) Anhydrous Na2CO3 b) Anhydrous CaCl2 c) Dry NaCl d) None of the above ANS Answer: (a) Q23) A firework gives out crimson colour light. It contains salt of ..[AFMC 1989] a) Ca b) Na c) Sr d) Ba ANS Answer:(c) Q24) Plaster of Paris is hardens by ... [ CPMT 1989] a) Giving off CO2 b) Changing into CaCO3 c) Combining with water d) Giving out water ANS Answer: (c) Q25) Which one of the alkaline earth metals shows some anomalous behavior and has the same electro negativity as aluminum? [ AIIMS 1985] a) Ba b) Sr c) Ca d) Be ANS Answer: (d) Q26) Formula for calcium cyanamide is .. [ Roorkee 1998] a) Ca(CN)2 b) CaC2N c) CaNCN

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d) CaCHNH2 ANS Answer: (c) Q27) The wire of flash bulb is made of ..[CPMT 1988] a) Mg b) Cu c) Ba d) Ag ANS Answer:(a) Q28) A firework gives out green colour light. It contains a slat of ..[ AFMC 1989] a) Na b) K c) Ba d) Ca ANS Answer: (c) Q25) Which one of the alkaline earth metals shows some anomalous behavior and has the same electro negativity as aluminum? [ AIIMS 1985] a) Ba b) Sr c) Ca d) Be ANS Answer: (d) Q26) Formula for calcium cyanamide is .. [ Roorkee 1998] a) Ca(CN)2 b) CaC2N c) CaNCN d) CaCHNH2 ANS Answer: (c) Q27) The wire of flash bulb is made of ..[CPMT 1988] a) Mg b) Cu c) Ba d) Ag ANS Answer:(a) Q28) A firework gives out green colour light. It contains a slat of ..[ AFMC 1989] a) Na b) K c) Ba

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d) Ca ANS Answer: (c) Q29) Which of the following are arranged in increasing order of solubility? a) CaCO3 < KHCO3 < NaHCO3 b) NaHCO3 < KHCO3 < CaCO3 c) KHCO3 < NaHCO3 < CaCO3 d) CaCO3 < NaHCO3 < KHCO3 ANS Lesser the lattice energy more is solubility Answer: (d) Q30) Which of the following does not liberate O2 in Bunsen burner ..[AFMC 1988] a) MgO b) NaNO3 c) Pb3O4 d) KClO3 ANS Except MgO all other gives Oxygen 2Pb3O4 → 6PbO + O2 2NaNO3 → 2naNO2 + O2 2KClO3 → 2KCl + 3O2 Answer: (a) Q31) Which of the following is different from the other three oxides? [ AFMC 1989] a) MgO b) SnO c) ZnO d) Cr2O3 ANS MgO is basic while other three are amphoteric in nature Answer:(a) Q32) Mixture of MgCl2 and MgO is called [ DPMT 1982] a) Portland cement b) Sorrel's cement c) Double salt d) None ANS Answer: (b) Q33) Setting of Plaster of Paris involves [ MP PMT 1985] a) Oxidation with atmospheric oxygen b) Combination with atmospheric CO2 c) Hydration to yield another hydrate d) Dehydration

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ANS CaSO4 . ½ H2O → CaSO4 . 2H2O Answer: (c) Q34) Out of the following elements which one do you expect to be most reactive chemically [ CPMT 1983] a) Be b) Ca c) Ba d) Sr ANS Ba have lower electrode potential thus more reactive Answer: (c) Q35) Which of the following are arranged in increasing order of solubility? [ AFMC 1987] a) CaCO3 < KHCO3 < NaHCO3 b) NaHCO3 < KHCO3 < CaCO3 c) KHCO3 < NaHCO3 < CaCO3 d) CaCO3 < NaHCO3 < KHCO3 ANS Answer:( ) Q36) Which of the following sulphates has highest solubility in water? [ AFMC 1990] a) BaSO4 b) CaSO4 c) BeSO4 d) MgSO4 ANS Answer: (c) Q37) Setting of cement is an ..[DPMT 1984] a) Exothermic reaction b) Endothermic reaction c) Neither exothermic nor endothermic d) None ANS A Answer: (a) Q38) The compound insoluble in acetic acid is .. a) Calcium oxide b) Calcium carbonate c) Calcium oxalate d) Calcium hydroxide ANS Except option 'c' all reacts with acetic acid

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Answer: (c) Q39) Portland cement is manufactured by using [ CPMT 1987] a) Lime stone, clay and sand b) Limestone, gypsum and sand c) Limestone, gypsum and alumia d) Limestone, clay and gypsum ANS Answer:(d) Q40) Which of the following statements is correct for alkaline earth metals? ..[NCERT 1990] a) They are diatomic and forms ions of M2- b) They are highly electronegative elements c) They are monoatomic and form ions of type M+ d) They are monoatomic and form ions of the type M2+ ANS Answer: (c) Q41) The alkaline earth metals Ba, Sr, Ca, and Mg may be arranged in the order of their decreasing first ionization potential as .. [ CPMT 1990] a) Mg, Ca, Sr, Ba b) Ca, Sr, Ba,Mg c) Sr, Ba, Mg, Ca d) Ba, Mg, Ca, Sr ANS As the size increases ionization potential decreases Answer: (a) Q42) the right order of the solubility of sulphates of alkaline earth metals in water is .. [ MPCEE 1993] a) Be > Ca > Mg > Ba > Sr b) Mg > Be > Ba > Ca > Sr c) Be > Mg > Ca > Sr > Ba d) Mg > Ca > Ba > Be > Sr ANS As the size of cation increases, their hydration energies decreases more rapidly than their lattice energies. Consequently the volatilities of sulpANS decreases down the group Answer: (c) Q43) A drying agent which absorbs carbon dioxide and reacts violently with water is .. [ BHU 1994] a) Sodium carbonate b) Alcohol c) Conc. sulphuric acid d) Calcium oxide ANS

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Answer:(d) Q44) Which of the alkaline earth metals is the strongest reducing agent? [ MP PMT 1995] a) Ca b) Sr c) Ba d) Mg ANS Ba have lower ionization energy thus stronger reducing agent Answer: (c) Q45) Which of the following is true for magnesium? [ Pb CET 1990] a) It is more electronegative than sodium b) It is manufactured by electrolysis of aqueous magnesium chloride c) It is strong reducing agent d) It resembles, in chemical properties, with its diagonally placed element Boron in III group of the Periodic table ANS Answer: (c) Q46) An atom with atomic number 20 is more likely to combine chemically with the atom whose atomic number is ..[CBSE PMT 1993] a) 11 b) 14 c) 16 d) 10 ANS Z = 20 have 2 electrons in outer most orbit , while Z = 16 have six electrons in outer orbit thus Z = 16 will accept two electrons from Z = 20 to form chemical bond Answer: (c) Q47) Which of the following metal ion plays important role in muscle contraction? [ CBSE PMT 1994] a) K+ b) Na+ c) Mg2+ d) Ca2+ ANS Answer:(d) Q48) Identify the correct statement? [ CBSE PMT 1995] a) Gypsum contains a lower percentage of calcium than plaster of Paris b) Gypsum is obtained by heating plaster of Paris c) Plaster of Paris can be obtained by hydration of gypsum d) Plaster of Paris is obtain by partial oxidation of gypsum ANS Answer: (a)

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Q49) Which of the following has correct increasing basic strength? [ CPMT 1992] a) MgO < BeO < CaO < BaO b) BeO < MgO < CaO < BaO c) BaO < CaO < MgO < BeO d) CaO < BaO < BeO < MgO ANS Basic character increases down the group Answer: (b) Q50) Melting point is lower for .. [ AFMC 1994] a) Be b) Mg c) Ca d) Sr ANS Answer: (b) Q51) Which of the following statement is false? ..[CBSE PMT 1994] a) Strontium decomposes water readily than beryllium b) Barium carbonate melts at higher temperature than calcium carbonate c) Barium hydroxide is more soluble in water than magnesium hydroxide d) Beryllium hydroxide is more basic than barium hydroxide ANS Beryllium hydroxide although amphoteric, is how ever less basic than barium hydroxide Answer:(d) Q52) A metal is burnt in air and the ash on moistening smells of NH3. the metal is ..[KCET 1996] a) Na b) Fe c) Mg d) Al ANS Mg burns in air to form Mg3N2 which then reacts with H2O to form NH3 Answer: (c ) Q53) Which of the following compound of cement sets at the slowest rate? [ CPMT 1992] a) Dicalcium silicate b) Tricalcium silicate c) Tricalcium aluminate d) Tetracalcium aluminoferrite ANS Dicalcium silicate 2CaO.SiO2 have higher SiO2 so it has slow setting rate, Answer: (a)

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Q54) All the following substances reacts with water. the pair that gives the same gaseous product is .. [ CBSE PMT 1994] a) K and KO2 b) Na and Na2O2 c) Ca and CaH2 d) Ba and BaO2 ANS Na and Ba gives Hydroxide + H2 Na2O2 and BaO2 gives hydroxide and H2O2 While K gives KOH+ H2 and KO2 gives O2 and H2O2 Ca + 2H2O → Ca(OH)2 + H2 CaH2 + 2H2O → Ca(OH)2 + 2H2 Answer: (c) Q55) Which of the following metal evolves hydrogen on reacting with cold dilute HNO3? [ Pb CET 1995] a) Mg b) Al c) Fe d) Cu ANS Answer:(a) Q56) The following compounds have been arranged in order of their increasing thermal stabilities. Identify the correct order K2CO3(I), MgCO3(II), CaCO3(III), BeCO3(IV) a) I < II < III < IV b) IV < II < III < I c) IV < II < I < III d) II < IV < III < I ANS Stability of carbonates increases down the group as the basic character increases Answer: (b) Q57) Which of the following has highest electrode potential? [ CPMT 1990] a) Be b) Mg c) Ca d) Ba ANS Answer: (a) Q58) The most electropositive amongst the alkaline earth metal is ..[MP PMT 1993] a) Beryllium b) Magnesium c) Calcium

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d) Barium ANS Barium have lowest ionization energy hence highest electropositive character Answer: (d) Q59) Among the following oxides, the one which is most basic is ..[CBSE PMT 1994] a) ZnO b) MgO c) Al2O3 d) N2O5 ANS N2O5 is acidic ZnO and Al2O3 is amphoteric MgO is basic Answer:(b) Q60) White enamel of our teeth is ..[Bihar CET 1995] a) Ca3(PO4)2 b) CaF2 c) CaCl2 d) CaBr2 ANS Answer: (b) Q61) Epsom salt is the hydrate of one of the following .. [CPMT 1990] a) Magnesium sulphate b) Ferrous ammonium sulphate c) Magnesium ammonium phosphate d) Calcium sulphate ANS Epsom salt is MgSO4 . 7H2O Answer: (a) Q62) The decreasing order of the second ionization potential of K, Ca, Ba is ...[ IIT 1993] a) K > Ca > Ba b) Ca > Ba > K c) Ba > K > Ca d) K > Ba > Ca ANS second ionization energy of K is highest because second electron is to be lost from inert gas core. Further because of large size of Ba its second ionization energy is lowered than smaller size Ca Answer: (a) Q63) Among the metals Be, Mg, Ca and Sr of group 2 ( or group IIA) of the periodic table, the least ionic chloride would be formed by.. [ DEC 1994]

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a) Mg b) Be c) Ca d) Sr ANS Due to high electronegativity and ionization potential Be will form covalent chloride Answer:(c) Q64) A salt on treatment with dil. HCl gives a pungent smelling gas and a yellow precipitate. the salt gives green flame test and a yellow precipitate with potassium chromate. the salt is ..[MP CEE 1996] a) NiSO4 b) BaS2O3 c) PbS2O3 d) CuSO4 ANS Flame test gives colour thus slat must have Ba ion When salt is treated with dil. HCl it gives pungent smell (SO2) and yellow ppt it must contain S2O3- Answer: (b) Q65) The atomic numbers of four elements are given below. Which one is an alkaline earth metal ..[AMU 1992] a) 10 b) 20 c) 30 d) 40 ANS Alkaline earth metals have two electrons more than the inert gas , Ar =18 which is inert gas , thus atomic number 20 must be Alkaline earth metal Answer: (b) Q66) Which of the following imparts brick red colour to the flame? [ AFMC 1994] a) Ca b) Ba c) Sr d) None of the above ANS Answer: (a) Q67) Presence of which of the following slat increases the rate of setting of plaster of paris a) NaCl b) KCl c) BaSO4 d) CuSO4 ANS

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Presence of NaCl increases the rate of setting of plaster of paris while borax or alum retard it Answer:(a) Q69) Which one of the following substance is used in laboratory for fast drying of neutral gases? .. [ CBSE PMT 1992] a) Phosphorous pentaoxide b) Active charcoal c) Anhydrous calcium chloride d) Na3PO4 ANS Answer: (a) Q70) To a clear solution of compound (X), a solution of BaCl2 is added and a heavy white precipitate is formed which does not dissolve in dil. HCl. the compound (X) is ..[ DEC 1994] a) A nitrate b) A bromide c) A sulphate d) A carbonate ANS Only sulphate reacts with BaCl2 solution to form a white ppt. of BaSO4, which is insoluble in dil HCl Answer: (c) Q71) Which of the following salts does not impart a colour to the flame? [ Pb CET 1995] a) LiCl b) KCl c) MgCl2 d) CaCl2 ANS Mg has very high ionization enthalpy which can be provided by Bunsen burner thus MgCl2 does not impart any colour to the flame Answer:(c) Q72) Calcium is obtained by the .. [ MP PMT 1996] a) Electrolysis of molten CaCl2 b) Electrolysis of solution of CaCl2 in water c) Reduction of CaCl2 with carbon d) Roasting of lime ANS Answer: (a) Q73) Amongst the following hydroxides, the one which has the lowest value of Ksp at ordinary temperature ( about 25°C) is ..[IIT 1990] a) Mg(OH)2 b) Ca(OH)2

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c) Ba(OH)2 d) Be(OH)2 ANS Be(OH)2 is lowest soluble implies lowest Ksp Answer: (d) Q74) Among the following: NaOH, Ca(OH)2, KOH and Zn(OH)2, the weakest base is ..[KCET 1993] a) NaOH b) Ca(OH)2 c) KOH d) Zn(OH)2 ANS Except Zn(OH)2 all others are hydroxides of alkali and alkaline earth metals thus are very strong base Answer: (d) Q75) Beryllium is placed above magnesium in the second group. Beryllium dust, therefore, when added to MgCl2 solution will ...[DPMT 1994] a) Have no effect b) Precipitate Mg metal c) Precipitate MgO d) Lead to dissolution of beryllium metal ANS Beryllium is weaker reducing agent than Mg, thus Mg cannot reduce to Mg2+ ions to Mg metal, thus have no effect Answer:(a) Q76) The solubility in water of sulphate's down the Be group is Be > Mg > Sr > Ba. This is due to.. [ CBSE PMT 1995] a) High heat of solution for smaller ions like BE2+ b) Increasing molecular weight c) Decreasing lattice energy d) Increase in melting points ANS Answer: (a) Q77) Electron configuration of calcium atom may be written as .. [ CBSE PMT 1992] a) Ne, 4p2 b) Ar, 4s2 c) Ne, 4s2 d) Ar, 4p2 ANS Answer: (b) Q78) Melting point of calcium halides decreases in order .. [ CPMT 1993] a) CaF2 > CaCl2 > CaBr2 > CaI2 b) CaI2 > CaBr2 > CaCl2 > CaF2

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c) CaBr2 > CaI2 >CaF2 > CaCl2 d) CaCl2 > CaBr2 > CaI2 > CaF2 ANS As the size of anion increases covalent character increases thus the melting point decreases Answer: (a) Q79) A metal salt solution forms a yellow precipitate with potassium chromate in acetic acid, a white precipitate with dilute sulphuric acid but gave no precipitate with sodium chloride or iodide. the white precipitate obtained when sodium carbonate is added to the metal salt solution will consist of .. [ AIIMS 1994] a) lead chromate b) basic lead chromate c) Barium Carbonate d) Strontium carbonate ANS Both Ba and Pb give yellow ppt when reacts with potassium chromate in acetic acid and white ppt with dil H2SO4 since the given salt do not give any ppt with NaCl or NaI salt then it must be salt of Ba Answer:(c) Q80) The first ionization energies of alkine earth metals are higher than those of the alkali metals. This is because... [ MP CEE 1996] a) There is an increase in the nuclear change of the alkaline earth metals b) There is a decrease in the nuclear charge of the alkaline earth metals c) There is no change in the nuclear charge d) None of the above ANS Answer: (a) Q81) The one which does not show variable valency is ..[ Pb CET 1997] a) Barium b) Titanium c) Copper d) Lead ANS Barium belongs to s block element shows only single valency while other belongs to 'p' block elements shows multiple valency Answer: (a) Q82) The compounds of alkaline earth metals have the following magnetic nature .. [ MP PMT 1998] a) Diamagnetic b) paramagnetic c) ferromagnetic d) Anti ferromagnetic

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ANS Alkaline earth metals forms M2+ ions in their compounds thus leaving all paired electrons in (n-1)s2p6 configuration and are diamagnetic Answer: (a) Q83) Limestone is not used in which of the following manufacturing process? a) Phosphorus from phosphate b) Iron from haematite c) Solvay process of sodium carbonate d) Portland cement ANS Answer:(a) Q84) Carnallite on electrolysis gives [ Kerala MEE 2003] a) Ca and Cl2 b) Na and CO2 c) Mg and Cl2 d) K and CO2 ANS Carnallite is ore of Mg ( MgCl2 KCl . 6H2O) on electrolysis gives Mg at cathode and Cl2 at anode Answer: (c) Q85) Alkaline earth metals form ions of the general formula ..[Pb CET 1997] a) M2+ b) M+ c) M d) M2- ANS Answer: (a) Q86)The solubility in water of sulphates down the Be group is Be > Mg > Ca > Sr > Ba. This is due to ..[AIIMS 1999] a) High ionization energy b) Increase in melting point c) Higher coordination number d) All of these ANS In crystalline sulphates, the coordination number of the ions increases from Be and so the lattice energy. thus, the solubility in water decreases Answer: (c) Q87) Which of the following has maximum ionization energy> [ Bihar CEE 2002] a) Ba → Ba+ + e- b) Be → Me+ + e- c) Ca → Ca2+ + 2e- d) Mg → Mg2+ + 2e- ANS

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Answer:(d) Q88) The solubilities of carbonates decrease down the magnesium group due to a decrease in ...[AIEEE 2003] a) Hydration energies of cations b) Inter ionic interaction c) Entropy of solution formation d) Lattice energies of solids ANS Answer: (a) Q89) For two ionic solids CaO and KI, identify the wrong statement among the following? [ CBSE PMT 1997] a) Lattice energy of CaO is much higher than that of KI b) KI is soluble in benzene c) CaO has high m.p. d) KI has high m.p. ANS Due to lower lattice energy of KI melting point of KI is much lower than CaO Answer: (d) Q90) halides of alkaline earth metals form hydrates such as MgCl2 . 6H2O, CaCl2.6H2O, BaCl2 . 2H2O and SrCl2 .2H2O. This shows that halides of group 2 elements ... [ Roorkee Screeing Test 2000] a) Are hygroscopic in nature b) Act as dehydrating agents c) Can absorb moisture from air d) All of the above ANS Answer: (d) Q91) Which of the following process is used in the extractive metallurgy of magnesium? [ IIT screening 2002] a) Fused salt electrolysis b) Self reduction c) Aqueous solution electrolysis d) Thermite reduction ANS Answer:(a) Q92) Which is insoluble in water? a) H2O b) HgCl2 c) Ca(NO3)2 d) CaF2 ANS Answer: (c)

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Q93) The first ionization potentials (eV) of Be and B respectively are ..[ CBSE PMT 1998] a) 8.29, 9.32 b) 9.32, 9.32 c) 8.29, 8.29 d) 9.23, 8.29 ANS The first ionization potential of Be(1s2, 2s2) is more than that of B(2s2, 2s2, 2p1) Answer: (d) Q94) Plaster of paris is used .. [ CPMT 2000] a) As a plaster for walls b) In dentistry and surgery c) In metallurgical process d) As drying agent ANS Answer: (a) Q95) The reaction of slaked lime with Cl2 gas gives.. [ kerala MEE 2000] a) only Ca(OCl)2 b) only CaCl2 c) Mixture of ca(OCl)2, Ca(OH)2, CaCl2 and H2O d) baryta water ANS Ca(OH)2 + Cl2 → CaOCl2 + H2O bleaching powder is a mixture of calcium hypochlorite. Ca(CCl)2 and calcium chloride Answer:(c) Q96) Which of the following ion forms a hydroxide highly soluble in water? [ DPMT 1979] a) Ni2+ b) K+ c) Zn2+ d) Al3+ ANS Answer: (b) Q97) One which is not dissolved by dilute hydrochloric acid is .. [ P. CET 1997] a) ZnS b) MnS c) BaCO3 d) BaSO4 ANS Answer: (d) Q98) Which of the following is incorrect a) Mg burns in air releasing dazzling light rich in UV rays

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b) CaCl2 . 6H2O when mixed with ice gives freezing mixture c) Mg cannot form complex d) Be can form complexes due to its very small size ANS Mg can form complexes and chlorophyll is one of such examples Answer: (c) Q99) On heating quick lime with coke in an electric furnace, we get ..[AIIMS 2001] a) Ca and CO2 b) CaCO3 c) CaO d) CaC2 ANS CaO + 3C → CaC2 + CO Answer:(d) Q100) In curing cement plaster, water is sprinkled from time to time. This helps in .... [ AIEEE2003] a) Developing interlocking needle like crystals of hydrated silicates b) Hydrated sand gravel mixed with cement c) Converting sand into silicic acid d) keeping it cool ANS Answer: (a) Q101) the correct order of increasing ionic character is ..[AFMC 1998] a) BeCl2 < MgCl2 < CaCl2 < BaCl2 b) BeCl2 < MgCl2 < BaCl2 < CaCl2 c) BeCl2 < BaCl2 < MgCl2 < CaCl2 d) BaCl2 < CaCl2 < MgCl2 < BeCl2 ANS Ionic character of chlorides increases as the size of the cation increases from Ne2+ to Ba2+ Answer: (a) Q102) Among the alkaline earth metals, the element forming predominantly covalent compound is ..[MP CEE 1999] a) Be b) Sr c) Ca d) Be ANS Due to small size of Be and greater polarising action on anion, Be forms covalent compounds Answer: (d) Q103) As alkaline earth metals ( except Be) tend to lose their valence electrons readily, they acts as [ Keralla MEE 2002]

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a) Weak oxidising agents b) Weak reducing agents c) Strong oxidising agents d) Bases ANS Alkaline earth metals acts as strong reducing agent, thus appropriate option is bases Answer:(d) Q104) Several blocks of magnesium are fixed to the bottom of ship to .. [AIEEE 2003] a) Make the ship lighter b) Prevent action of water and salt c) Prevent puncturing by under-sea rocks d) Keep away the hark ANS Answer: (b) Q105) Property of the alkaline earth metals that increases with their atomic number is ... [ IIT 1997] a) Ionization energy b) Solubility of their hydroxides c) Solubility of their sulphates d) electro negativity ANS Answer: (b) Q106) A metal X on heating in nitrogen gas gives Y, Y on treatment with H2O gives a colourless gas which when passed through CuSO4 solution gives a blue colour. Y is .. [ DEC 2000] a) Mg(NO3)2 b) Mg3N2 c) NH3 d) MgO ANS 3Mg + N2 → Mg3N2 Mg3N2 + 6H2O → 3Mg(OH)2 + 2NH2 ↔ CuSO4 + 4NH3 → [Cu(NH3)4]SO4 (blue complex) Answer: (b) Q107) The number of covalent bonds formed by beryllium is ... [ Manipal PMT 2001] a) 2 b) 3 c) 4 d) 5 ANS

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Be have two valence electrons thus can form only two covalent bonds Answer:(a) Q108) 30g of Mg and 30g of O2 are reacted and residual mixture contains.. a) 60 g of Mg only b) 40g of MgO and 20g of O2 c) 45g of MgO and 15g of O2 d) 50g of MgO and 10g of O2 ANS 2Mg + O2 → 2MgO Thus 48g of Mg requires 32g of O2 to form 80g of MgO Therefore30g of Mg requires 20g of O2 to form 50g of MgO the residual mixture contains 50g MgO and 10g of O2 Answer: (d) Q109) metals belonging to the same group in the periodic table are ..[ MP PMT 1998] a) Mg and Na b) Mg and Cu c) Mg and Ba d) Mg and K ANS Answer: (c) Q110) the set representing correct order of first ionization potential is ..[ IIT screening test 2001] a) K > Na > Li b) Be > Mg > Ca c) B > C > N d) Ge > Si > C ANS On moving from top to bottom in group Ionization potential decreases as the size of the atom increases Answer: (b) Q111) A solution of MgCl2 in water has pH .. [ MP PMT 2002] a) < 7 b) > 7 c) 7 d) 14.2 ANS MgCl2 is salt of strong base and acid Answer:(c) Q112) Fire extinguishers contain H2SO4 and ...[AFMC 1980] a) NaHCO3 and Na2CO3 b) NaHCO3solution c) Na2CO3 d) CaCO3

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ANS Answer: (a) Q113) The first ionization potential of Mg is ..[ CPMT 1997] a) Less than Al b) More than Al c) Equal to Al d) Zero ANS First ionization potential of Mg is more than Al as the electron has to be removed from completely filled s-valence shell of Mg Answer: (b) Q114) A chloride dissolves appreciably in cold water. When placed on a Pt. wire in Bunsen flame, no distinctive colour is noted. Which cation could be present a) Be2+ b) Ba2+ c) Pb2+ d) Ca2+ ANS ionization energy of Be is very high, which can not be provided by Bunsen flame and Be2+ ions do not impart colour to the flame Answer: (a) Q115) A metal M readily forma water soluble sulphate MSO4, water insoluble M(OH)2 and oxide MO which becomes inert on heating. The hydroxide is soluble in NaOH. The M is ..[ AIEEE 002] a) Be b) Mg c) Ca d) Sr ANS BeSO4 is water soluble Be(OH)2 and BeO is water insoluble Be(OH)2 is soluble in NaOH giving sodium beryllate Na2BeO2 Answer:(a) Q116) The substance not likely to contain CaCO3 is ... [ AIEEE 2003] a) Calcined gypsum b) Sea shells c) Dolomite d) A marble statue ANS Answer: (a) Q117) What is X in the following reaction? MgCl2 + 2H2O → X + 2HCl + H2O a) MgO

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b) Mg c) Mg(OH)2 d) Mg(OH)Cl ANS Answer: (a) Q118) Chemical A is used for water softening to remove temporary hardness. A reacts with Na2CO3 to generate caustic soda. When CO2 is bubbled through A, it turns cloudy. What is the chemical formula of A....[ AIIMS 1999] a) CaCO3 b) CaO c) Ca(OH)2 d) Ca(HCO3)2 ANS Ca(OH)2 + Na2CO3 → 2NaOH + CaCO3 Answer: (c) Q119) As the nuclear charge increases from neon to calcium, the orbital energies...[kerala MEE 2002] a) Increases b) Increase very rapidly c) Increases very slowly d) remains constant ANS After Neon ( At no 18) next electron enters into 4s orbitals which is lower in energy than 3d orbital Answer:(d) Q120) Initial setting of cement is mainly due to .. [ kerala CEE 2003] a) Hydration and gel formation b) Dehydration and gel formation c) Hydration and hydrolysis d) Hydration and oxidation ANS Answer: (a) Q121) Leblance process is employed in the manufacture of .. [CPMT 1982] a) Baking soda b) Washing soda c) Potash d) Plaster of paris ANS Answer: (c) Q122) The metallic lustre exhibited by sodium is explained by .. [ IIT 1987] a) Diffusion of sodium ions b) Oscillation of loose electrons c) Excitation of free protons

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d) Existence of body centered cubic lattice ANS Answer: (b) Q123) Which of the following oxides is formed when potassium metal is burnt in excess air? [ Pb. CET 1990] a) K2O b) KO c) KO2 d) K2O2 ANS Potassium forms super oxide KO2 Answer:(c) Q124) Salt used for performing bead test in qualitative inorganic analysis is .. [MLNR 1991] a) K2SO4. Al2(SO4 .6H2O b) FeSO4 . (NH4)2SO4 .6H2O c) Na(NH4)HPO4 .4H2O d) CuSO4 . 5H2O ANS Answer: (c) Q125) Sodium carbonate reacts with SO2 in aqueous medium to give .. [ MP PMT 1985] a) NaHSO3 b) Na2S2O3 c) NaHSO4 d) Na2SO4 ANS Na2CO3 + 2SO2 + H2O → 2NaHSO3 + CO2 Answer: (a) Q126) Sodium metal cannot be stored under.. [ CPMT 1988] a) Benzene b) Kerosene oil c) Alcohol d) Toluene ANS Sodium reacts with alcohol Answer: (c) Q127) The properties of lithium are similar to those of Mg. This is because ..[NCERT 1990] a) Both have nearly same size b) The ratio of their charge to size is nearly same c) Both have similar electron configuration d) Both are found together in nature

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ANS Answer:(b) Q128) The alkali metal that reacts with nitrogen directly to form nitride is ... [Roorkee 1992] a) Li b) Na c) K d) Rb ANS Li reacts with nitrogen directly to form Li3N Answer: (a) Q129) Which of the following imparts violet coloration to the non-luminous flame of Bunsen burner? [ CPMT 1985] a) NaCl b) BaCl2 c) CaCl2 d) KCl ANS Answer: (d) Q130) Which of the following atoms will have the smallest size? [ CBSE PMT 1989] a) Mg b) Na c) Be d) Li ANS With in the period size decreases from left to right Answer: (c) Q131) Potassium metal is commercially prepared by the reduction of molten KCl with metallic sodium at 850°C. This method is based upon the following principle. ..[Pb CET 1990] a) Sodium is more reactive than potassium at this temperature b) Potassium being more volatile distills off thus shifting the reaction forward c) Sodium prefers to bind to chloride ions in preference to potassium ions d) Potassium and sodium form an alloy at this temperature ANS Answer:(c) Q132) Which of the following does not illustrate the anomalous properties of Li? [ MP CET 1993] a) The m.p. and b.p. of Li are comparatively high b) Li forms a nitride unlike group 1 metals c) Li is much softer than the other I group metals d) Li+ and its compounds are more heavily hydrated than those of the rest of the group

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ANS Li has smaller size and forms strong metallic bonds thus it is harder than rest of the elements in the group Answer: (c) Q133) The pair of compounds which cannot exist together in solution is ... [ IIT 1986] a) NaHCO3 and NaOH b) NaHCO3 and H2O c) NaHCO3 and Na2CO3 d) Na2CO3 and NaOH ANS NaHCO3 is a acidic salt , it reacts with NaOH to form, Na2CO3 and H2O Answer: (a) Q134) Which of the following alkali metal hydroxides is the strongest base? [ PbCET 1990] a) LiOH b) NaOH c) KOH d) CsOH ANS Lower the ionization energy more is basic character. Answer: (d) Q135) Microcosmic salt is .. [CPMT 1991] a) Na2HPO4 . 2H2O b) (NH4)2HPO4 c) Na(NH4)HPO4 .4H2O d) None of above ANS Answer:(c) Q136) In the preparation of sodium carbonate (Na2CO3) which of the following is used? ..[AFMC 1992] a) Slaked lime b) Quick lime c) Lime stone d) Sodium hydroxide ANS Lime stone is used for production of CO2 Answer: (c) Q137) Which is manufactured by electrolysis of fused NaCl? ..[CPMT 1983] a) NaOH b) Na c) NaClO d) NaClO3

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ANS Answer: (b) Q138) When CO2 is bubbled into aqueous solution of Na2CO3 the following is formed [MP PMT 1986] a) NaOH b) NaHCO3 c) H2O d) OH- ANS Na2CO3 + CO2 + H2O → 2NaHCO3 Answer: (b) Q139) Which of the following compounds has the lowest anion to cation size ratio? [ NCERT 1990] a) LiF b) NaF c) CsI d) CsF ANS Answer:(d) Q140) Sodium conducts electricity because .. [Pb CET1991] a) It is a soft alkali metal b) It has only one electron in the outermost orbit c) It has mobile electrons d) It gives hydrogen with water ANS Answer: (c) Q141) Molecular formula of Glauber's salt is .. [ IIT 1985] a) MgSO4 . 7H2O b) CuSO4 .5H2O c) FeSO4 . 7H2O d) Na2SO4 . 10H2O ANS Answer: (d) Q142) Among alkali metal salts, the lithium salts are the poorest conductors of electricity in aqueous solution because of .. [Pb CET 1989] a) Easy diffusion of Li+ ions b) Lower ability of Li+ ions to polarize water molecules c) Lowest charge to radius ratio d) Higher degree of hydration of Li+ ions ANS Answer: (d) Q143) The gas evolved on heating Na2CO3 is ..[CPMT 1990] a) CO2

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b) CO c) Water gas d) No gas ANS Answer:(d) Q144) The correct sequence of the alkali metals in the group is ... [ AFMC 1992] a) Fr, Na, K, Rb, Cs, Li b) Li, Na, K, Rb, Cs, Fr c) Na, K, Rb, Cs, Fr, Li d) Rb, Cs, Li, Na, K ANS Answer: (b) Q145) Nitrogen can not be prepared by heating .. [ IIT 1985] a) KNO3 b) Pb(NO3)2 c) Cu(NO3)2 d) AgNO3 ANS Only nitrates of heavy metals and lithium decompose on heating to produce NO2 Answer: (a) Q146) The formula of nitre is ... [CPMT 1989] a) KNO3 b) NaNO2 c) NaCl d) Na2CO3 ANS Answer: (a) Q147) NaCl crystal consists of .. [ Vellore PMT 1991] a) NaCl molecules b) Na and Cl atoms c) Na+ and Cl- ions d) Na- and Cl+ ions ANS Answer:(c) Q148) The chloride of an element A gives a neutral solution in water. In the periodic table, the element A belongs to ...[ AIIMS 1992] a) First group b) Third group c) Fifth group d) First transition series ANS Answer: (a) Q149) Which of the following is radioactive? [ BHU 1992]

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a) Na 23 b) K39 c) K40 d) Ca40 ANS Answer: (c) Q150) Compared to alkali earth metals, the alkali metals exhibit... [CBSE PMT 1990] a) Smaller ionic radii b) Highest boiling points c) Greater hardness d) Lower ionization energies ANS Answer: (d) Q151) Which of the following is more basic ..[Vellore PMT 1991] a) Na2O b) BaO c) Al2O3 d) As2O3 ANS Alkali metals are most basic followed by alkaline earth metals Answer:(a) Q152) Which of the following has minimum value of cation/anion ratio ..[CBSE PMT 1993] a) NaCl b) KCl c) MgCl2 d) CaF2 ANS Down the group size of cation increases while in period size decreases thus Mg2+ is smallest. While Cl- is bibber than F-. Thus MgCl2 is correct option Answer: (c) Q153) Chile salt petre is ..[CPMT 1984] a) NaNO3 b) Na2SO4 c) NKO3 d) Na2S2O3 ANS Answer: (a) Q154)An aqueous solution of sodium sulphate is electrolysed using inert electrodes. the products at the cathode and anode are respectively a) H2, O2 b) O2, H2 c) O2, Na

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d) O2, SO2 ANS Since the solution is dilute and electrodes are neutral, electrolysis of water will take place Answer: (a) Q155) Which of the following has the highest solubility product? a) KOH b) CsOH c) LiOH d) RbOH ANS CsOH have highest solubility thus higher solubility product Answer:(b) Q156) Crude common salt is hygroscopic because of presence of impurities of ...[SCRA 1991] a) CaSO4 and MgSO4 b) CaCl2 and MgCl2 c) CaBr2 and MgBr2 d) Ca(HCO3)2 and Mg(HCO3)2 ANS Answer: (b) Q157) Causticisation process is used for the preparation of .. [CPMT 1985] a) Caustic soda b) Caustic potash c) Baryata solution d) Slaked lime ANS Na2CO3 + Ca(OH)2 → CaCO3↓ + 2NaOH (Caustic soda) Answer: (a) Q158) Which one of the following properties of alkali metals increases in magnitude as the atomic number rises [ CBSE PMT 1989] a) Ionic radius b) Melting point c) Electronegativity d) First ionization energy ANS Answer: (a) Q159) Washing soda has formula .. [CBSE PMT 1990] a) Na2CO3 .7H2O b) Na2CO3 .10H2O c) Na2CO3.3H2O d) Na2CO3 ANS

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Answer:(b) Q160) Which of the following has lowest thermal stability? [ CPMT 1988] a) Li2CO3 b) Na2CO3 c) K2CO3 d) Rb2CO3 ANS Weaker base, less stable is its carbonate. Since LiOH is weakest base therefore Li2CO3 Answer: (a) Q161) Which compound show the highest lattice energy? [ CBSE PMT 1993] a) RbF b) CsF c) NaF d) KF ANS With the same anion, smaller the size of the cation higher is the lattice energy Answer: (c) Q162) Which of the following compounds is used in gunpowder? [ Rohatak PMT 1994] a) NaNO3 b) KNO3 c) LiNO3 d) None ANS Answer: (b) Q163) Identify the correct statement.. [Pb PMT 1998] a) Elemental sodium can be prepared and isolated by electrolysis of aqueous solution of NaCl b) elemental Na is a strong oxidising agent c) Elemental Na is insoluble in NH3 d) Elemental Na is easily oxidised ANS Answer:(d) Q164) A deliquescent white crystalline hydroxide X reacts with a nitrate Y to form another hydroxide which decomposes to give a insoluble brown layer of its oxide. X is a powerful cattery and breaks down the proteins of skin flesh to a pasty mass. X and Y are ... [ Roorkee 2000] a) NaOH, AgNO3 b) NaOH, Zn(NO3)2 c) NaOH, Al(NO3)3 d) Ca(OH)2, HgNO3 ANS

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NaOH + AgNO3 → AgOH + NaNO3 AgOH is unstable decomposes 2AgOH → Ag2O + H2O Ag2O is Brown in colour NaOH is powerful cattery and breaks down the skin protein to pasty mass Answer: (a) Q165) Strongest bond is between ..[CBSE PMT 1993] a) CsF b) NaCl c) Both (a) and (b) d) None of the above ANS According to Fajan rule, ionic character increases with increase in size of the cation and decreases in size of the anion. Thus CsF has higher ionic character than NaCl and bond in CsF is stronger than NaCl Answer: (a) Q166) With increase in atomic weight melting points of the alkali metals... [MP PMT 1995] a) Increases b) Decreases c) Remains constant d) Do not show definite trend ANS In alkali metals metallic bonding become weak thus melting point decreases Answer: (b) Q167) Anhydrous mixture of KF and HF contains which type of ions? [ JIPMER 2000] a) K+, H+, F- b) (KF)+ (HF)- c) KH+, F- d) K+, HF2- ANS KF + HF → K+ [HF2]-. Answer:(d)

Q168) Oxone is ...[Manipal PMT 2001] a) CaO b) N2O c) Na2O2 d) NaBO3 ANS Answer: (c) Q169) Which of the following statement is false for alkali metals? [ MLNR 1994]

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a) Lithium is strongest reducing agent b) Sodium is amhoteric in nature c) Li+ is exceptionally small d) Alkali metals give blue solution in liquid ammonia ANS All alkali metals are strong base Answer: (b) Q170) When NaOH is made, the gas released at the cathode is ..[CPMT 1996] a) Cl2 b) H2 c) O2 d) H2O ANS At anode chlorine is liberated Answer: (b) Q171) Which of the following has the highest melting point? [ DPMT 1998] a) NaCl b) NaF c) NaBr d) NaI ANS Due to larger lattice enthalpy of NaF higher melting point Answer:(b) Q172) KO2 (potassium super oxide) is used in oxygen cylinders in space and submarine because ..[AIEEE 2002] a) Absorbs CO2 and O2 contents b) Eliminates moisture c) Absorbs CO2 d) Produce Ozone ANS Answer: (a) Q173) Fires, that result from the combustion of alkali metals can be extinguished by ..[KCET 1994] a) CCl4 b) Sand c) Water d) Kerosene ANS CCl4 is low boiling point, highly non inflammable heavy liquid. It vapour surrounded the fire thereby cutting of air supply. As a result, fire is extinguished. Answer: (a) Q174) Alkalimetals are generally extracted by ... [ Pb CET 1997] a) Reduction methods

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b) Double decomposition methods c) Displacement method d) Electrolytic methods ANS Answer: (d) Q175) Cs+ ion imparts violet colour to the flame. This is due to the fact that the emitted radiations have ..[Haryana CEET 1999] a) High energy b) Low energy c) Low wavelength d) None of these ANS Answer:(a) Q176) In electrolysis of NaCl when Pt electrode is taken than H2 is liberated at cathode while with Hg cathode it forms sodium amalgam. The reason for this is ..[CBSE PMT 2002] a) Hg is more reactive than Pt b) More voltage is required to reduce H+ at Hg than at Pt c) Na is dissolved in Hg while it does not dissolve in Pt d) Concentration of H+ ions is larger when Pt electrode is taken ANS H+ ions are discharged at higher potential when Hg cathode is used than Pt cathode Answer: (b) Q177) Which compound shows the highest lattice energy? [CBSE PMT 1993] a) RbF b) CsF c) NaF d) KF ANS With same anion smaller the cation higher the lattice energy Answer: (c) Q178) Alkali metals displace hydrogen from water forming bases due to the reason that ... [Haryana CEET 1994] a) They are far above the hydrogen in electrochemical series based on oxidation potential

b) They are far below the hydrogen in electrochemical series based on oxidation potential c) Their ionization potential is less than that of other elements d) They contain only one electron in their outermost shell ANS Alkali metals are electropositive than Hydrogen

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Answer: (a) Q179) Which one of the following has highest electropositive character? [ MP PMT 1998] a) Cu b) Cs c) Ba d) Cr ANS Out of the options given Cs is alkali metal have highest electropositive character Answer:(b) Q180) Lithium is strongest reducing agent among alkali metals due to which of the following factor/ [ DEC 2000] a) Ionization energy b) Electron affinity c) Hydration energy d) Lattice energy ANS Answer: (c) Q181) In Solvay ammonical process, sodium bicarbonate is precipitate due to .. [CPMT 1993] a) Presence of NH3 b) Reaction with CO2 c) Reaction with brine solution d) Reaction with NaOH ANS NH4HCO3 + NaCl → NaHCO3 ↓ + NH4Cl Answer: (c) Q182) Which of the following statements is correct for CsBr3? .. [IIT 1996] a) It is a covalent compound b) It contains Cs3+ and Br- ions c) It contains Cs+ and Br3- ions d) It contain Cs+, Br- and Br2 molecules ANS Answer: (c) Q183) In certain respects. lithium differs from other alkali metals. The main reason for this is ...[MP PMT 1998] a) small size of lithium atom and Li+ ion

b) Extremely high electropositivity of Li c) Greater hardness of Li d) Hydration of Li+ ion ANS Answer:(a)

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Q184) When K2O is added to water, the solution is basic because it contains a significant concentration of ...[ AIIMS 2001] a) O22- b) O3- c) OH- d) K+ ANS Answer: (c) Q185) The reactivity of the alkali metals sodium with water is made use of ? ..[M PMT 1994] a) In drying of alcohol b) In drying of ammonia solution c) In drying of Benzene d) As general drying agent ANS Answer: (c) Q186) Which of the following statement is incorrect: [ AMU 1997] a) Sodium is the most abundant metal in earth's crust b) Sodium is the most abundant metallic element in sea water c) Melting and boiling points of alkai metals decreases down the group d) Ionic character of alkali metal halides decreases down the group ANS Answer: (d) Q187) When CO is passed over solid NaOH heat to 200°C , it forms ..[CBSE PMT 1998] a) Na2CO3 b) H2CO3 c) HCOONa d) All ANS NaOH + Co → HCOONa ( sodium formate) Answer:(c) Q188) Which of the following has the highest conductivity? [ Haryana CEET 1999] a) Li+ b) Cs+ c) Na+ d) K+ ANS

Cs has highest mobility thus highest conductivity Answer: (b) Q189) A combustible gas is liberated when caustic soda solution is heated with ..[Raj. PMT 1994]

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a) S b) NH4Cl c) I2 d) Zn ANS Zn + NaOH → Na2ZnO2 + H2 ↑ Hydrogen is combustible gas Answer: (d) Q190) Sodium nitrate decomposes above 800°C to give ..[IIT 1998] a) N2 b) O2 c) NO2 d) Na2O ANS 2NaNO3 → 2NaNO2 + O2 Answer: (b) Q191) On heating sodium metal in a current of dry ammonia, the compound formed is ...[KCET 2000] a) Sodium amide b) Sodium azide c) Sodium nitride d) Sodium hydride ANS 2Na + 2NH3 → 2NaNH2 + H2 Answer:(a) Q192) On dissolving moderate amount of sodium metal in liquid NH3 at low temperature, which of the following does not occur? .. [AIIMS 2003] a) Blue coloured solution is obtained b) Na+ ions are formed in the solution c) Liquid NH3 solution becomes good conductor of electricity d) Liquid NH3 solution remains diamagnetic ANS On dissolving moderate amount of Na metal in liquid NH3, the solution is blue in colour and paramagnetic but not diamagnetic Answer: (c) Q193) Which of the following properties is not true for an alkali metal? [CPMT 1993] a) Low atomic volume b) Low ionization energy c) Low density d) Low electronegativity ANS

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In any period alkali metals have lowest density ( except noble gas) , therefore alkali metals have large volume Answer: (a) Q194) Which of the following reacts with water at high rate? [ AFMC 1995] a) Li b) K c) Na d) Rb ANS Ionization energy decreases in group from top to bottom, thus Rb have lowest ionization energy, so reacts with water at higher rate Answer: (d) Q195) The electronic configuration of metal M is 1s2, 2s2, 2p6, 3s1. The formula of its oxide would be ... [MP PMT 1998] a) MO b) M2O c) M2O3 d) MO2 ANS Answer:(b) Q196) The alkali metal that reacts with nitrogen directly to form nitride is .. [ MP PMT 2000] a) Li b) Na c) K d) Kb ANS 6Li + N2 → 2Li3N Answer: (a) Q197) Which of the following is known as fusion mixture? [ CBSE PMT 1993] a) Mixture of Na2CO3 + NaHCO3 b) Na2CO3 . 10H2O c) Mixture of K2CO3 + Na2CO3 d) NaHCO3 ANS Answer: (c) Q198) Sodium is made by the electrolysis of molten mixture of about 40% NaCl and 60% CaCl2 because...[CBSE PMT 1995] a) CaCl2 helps in conduction of electricity b) This mixture has a lower melting point than NaCl

c) Ca2+ can displace Na from NaCl d) Ca2+ can reduce NaCl to Na

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ANS Answer: (b) Q199) The stability of the following alkali metal chlorides follows the order .. [MP PMT 1998] a) LiCl > KCl > NaCl > CsCl b) CsCl > KCl > NaCl > LiCl c) NaCl > KCl > LiCl > CsCl d) KCl > CsCl > NaCl > LiCl ANS Stability depends on enthalpy of formation more the negative value of enthalpy of formation more stability Answer:( ) Q200) When sodium is treated with sufficient oxygen/air the product obtain is ...[AFMC 2002] a) Na2O b) Na2O2 c) NaO2 d) NaO ANS Answer: (b)

AN Sir Classes !84

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