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Exercise 1: Ammonia NH3
NH3 ammonia is a gas injected into cultivated land to improve the development of green plants and helpincrease crop production. It is used in refrigeration systems, but any leak in the pipesof these appliances releases ammonia into the air, which irritates the eyes and causespoisoning.
1. Document 1 represents the Lewis structure of the ammonia molecule:
1.1. What is the valence of the hydrogen atom?1.2. Specify the number of valence electrons of the nitrogen element.1.3. Identify the type of bonds in this molecule.
2. Document 2 represents the charge of the electron cloud of each of the N and H atoms.- Copy and complete the following table:
Atoms Charge of nucleus Electronic configuration Position in the periodictable
NH
3. The synthesis of ammonia is an oxidation-reduction reaction. This reaction isrepresented by the following equation: N2 + 3H2 2NH 3
3.1 - Choose from the oxidation numbers given below that which corresponds to theoxidation number of the nitrogen element in the NH3 ammonia molecule.a) o.n of (N) = 0 b) o.n of (N) = + I c) o.n of (N) = -III d) o.n of (N) = +III
3.2. Identify the species undergoing the reduction.3.3. Extract from the text the harmful effects of NH3 ammonia on the human body.
Exercise 2: Calcium
Calcium plays an important role in bone formation. Too little calcium in the diet, especially during periodsof bone growth, can lead to soft bones that break easily.
1. Calcium has four isotopes. The relative abundance of these varieties of atoms is shown in the table below:Calcium is located on the fourthrow (period 4) and in the secondcolumn (group II) of the periodictable.
1.1. Determine the atomic number of the calcium element1.2. Compare the composition of the nuclei of the four stable calcium isotopes.1.3. Give the electronic configuration of the element located just above the calcium.1.4. Draw from the text, the influence of a diet poor in calcium.
2. Fluorine is a yellowish gas of formula F2. Fluorine gas reacts with alkaline earth, it forms magnesiumfluoride, calcium fluoride CaF2 ... etc).The fluorine atom has seven valence electrons.
2.2. Explain the formation of the bond in the calcium fluoride compound (CaF2).2.3. Choose from the properties below those that represent this compound (CaF2).
Mass number (A) 40 42 43 44
Relative abundance (%) 96,941 0,647 0,135 2,086
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Molecular compound - low melting points - non-electrolyte in aqueous solution - ionic compound - highmelting points and electrolyte in aqueous solution.
Exercise 3: A Toxic Spot Remover
The 1,2-dichloroethene of molecular formula C2H2Cl2, is an efficient spot remover but it is toxic even insmall quantity. So, it should not be inhaled.
1. A molecule of 1,2-dichloroethene consists of the three elements: carbon, hydrogen and chlorine,
which are represented respectively by the atomic symbols: C126 , H1
1 and Cl3517 .
1.1. Write the electron configuration of each of these three atoms.1.2. Copy and fill in the following table. (The relative charge of one proton= + 1)
2. Identify the type of the bond between the two carbon atoms in the adjacent molecule.3. The molecules (C2H2Cl2) that enter the organism are not eliminated as they are, but
they are transformed in the liver into toxic product of formula C2H2O2Cl2.
3.1. Give the Lewis dot symbol of an oxygen atom, knowing that it has six valence electrons.3.2. Specify the valence of an oxygen atom.3.3. Write a Lewis structure of the molecule C2H2O2Cl2, where the bond between the two carbon atoms issingle covalent bond.3.4. Pick up why the molecules (C2H2Cl2) are toxic.
Exercise 4: Chemical Composition of Banana.
Banana contains compounds of potassium (k) and sodium (Na), it is a natural treatment for manydiseases! Comparing to the apple, banana contains four times more proteins (which contain mainly theelement nitrogen, three times more phosphorous and five times more vitamin A!Banana can be a good helper for persons who hope to stop smoking. Vitamins B6 and B12, as thepotassium and the magnesium (Mg), help the body to recover from the effects of the absence of nicotine.Given: The electron configurations of: Mg: K2, L8, M2; P: K2, L8, M5; K: K2, L8, M8,N1 et N: K2, L5.
1. Identify among the given elements (Mg, P and N),those that belong to the same period (line) and thosethat belong to the same group (column).
2. Determine the relative charge of the electroniccloud of a magnesium atom.(Relative charge of one electron = -1)
Element Charge of theNucleus
Column row Valence
Chlorine
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3. Potassium of atomic number Z = 19, is found in the nature as mixture of three isotopes. Therelative abundance of the atoms is shown in the following histogram.
Compare the composition of the nucleus of potassium isotopes.
4. Nitrogen (N) is the element that constitutes proteins and help plants to develop.4.1.Give the Lewis dot symbol of nitrogen atom N.4.2.Explain the formation of the bonds in nitrogen gas N2.
5. Tell, referring to the text why banana can be a good helper for persons who desire to stop smoking.
Exercise 5: Silicon
Silicon of symbol Si a metalloid used in fabrication of solar cells and transistors. It is prepared from puresand.
1. The symbol of the nucleus of silicon atom is 2814 Si
In the following table, only one proposed answer for each question is correct. Write the number of eachquestion then choose by justification the correct answer.
2. The silicon is found in nature as mixture of three isotopes. The relative abundance of these varietiesof atoms is shown in the table below.Mass number A 28 29 30
Relative abundance (%) 90 6 4Document 1
2.1.Compare the composition of nuclei of the three atoms of silicon.2.2.What is the heaviest silicon isotope???2.3.Determine the charge of electronic cloud of the first two silicon isotopes. Deduce the one of the
third isotope. (Relative charge of 1 electron = -1)3. Pick out from the text the uses of silicon.
AnswersN Questions
a b c
1
The nucleus of this atomcontains
14 protons and 28neutrons
14 protons and14neutrons
14 protons and 42neutrons
2The electron configuration ofthis atom is :
K2 L8 M4 K2 L6 M6 K2 L8 M8
3The position of this elementin the periodic table :
(groupe IV, période 4)(colonne 14, ligne 4 )
(groupe IV, période 3 )(colonne 14, ligne 3 )
(groupe III, période4)
| (colonne 13, ligne4)
4 The valence of this atom is : 4 6 8
Atom Period (line ) Column
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Exercise 6: Ethanol
Ethanol (C2H6O) is used as solvent for varnishes, perfumes,paintings ... It is also used as an antiseptic, an agent that reducesand prevents infection by eliminating the microorganisms thatcause disease.
1. Referring to document 1:1.1.Write the electron configuration of the 2 atoms: carbon and
hydrogen.1.2.Deduce the atomic number of carbon element.
Document 12. Referring to document 2:
2.1. Show that this document represents an atom.2.2. Give the symbol of oxygen nucleus atom.2.3.Determine the position of oxygen in the periodic table.
3. Referring to document 1 and document 2:3.1. Write the Lewis representation of each atom: carbon, hydrogen and oxygen.3.2. Deduce the valence of each of the above atom.
4. Give the Lewis representation of the molecule C2H6O, such the bond between the two carbon atoms issingle covalent bond.
Exercise 7: Magnesium oxide
Magnesium oxide is the oldest magnesium salts, described in a former medical dictionary has a highcontent of magnesium elementary 60.3%. But assimilation is bad enough as solubility. White powder, alsocalled "chalk", magnesium oxide, or periclase is used as an active ingredient in many medicines, to regulatethe levels of magnesium (Magnosol, Sympathyl ...) or fight against the stomach pain.
1. The histograms below show the constituents of the nucleus of each atom: magnesium and oxygen.
1.1.Reproduce and complete the table below:
Atomic number Mass number Electronic configuration
Oxygen
Magnesium
1.2.Write the Lewis representation of the atoms: oxygen and magnesium.
Carbon 2 14 (G:IV)Hydrogen 1 1(G:I)
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1.3.Justify if the following statement are true.
The oxygen atom located on the line 2 (period 2) of the periodic table. Magnesium atom belongs to the column 2 (group 2) of the periodic table.
2. The magnesium metal (Mg) reacts with the oxygen (O2), to give the compound magnesium oxide MgO.- Explain the formation of bond in the compound of magnesium oxide.
3. List by referring to the text the importance of magnesium oxide.
Exercise 8: Minerals of milk
Minerals are chemical elements needed for the functioning of the human body. The following table showsthe mass in mg of some chemical elements contained in 100 g of milk.
Symbol of element K Ca Cl P Na
Mass in mg 139 133 105 88 75
Given: 19 K : K2 L8 M8 N1; ZCa : K2 L8 M8 N2 ; 17Cl :K2 L8 M7; 15P : K2 L8 M5
; et 11Na : K2 L8 M1
1. Answer by true or false then correct the false statement1.1.Potassium and calcium have similar chemical properties.1.2. Phosphorus is found in column 15 and row 3 in the periodic table.1.3. The most stable ion of sodium is Na+.1.4.The valence of P atom is 5.
2. Chlorine (Cl) form with phosphorus (P), the compound PCl3 and with potassium the compound KCl.2.1. Give the Lewis dot symbol of each of the atoms: K, Cl and P.2.2. What is the Lewis dot representation of this compound PCl3. Deduce the nature of bonding
between the phosphorus atom and each atom of chlorine.2.3.Explain the bond formation in the compound potassium chloride.
3. Calcium ion Ca2+ is essential for the formation of teeth and bones and other tissues of the human body.The deficiency of calcium ions provokes a disease called osteoporosis.
(Relative charge of one proton = + 1 ; Relative charge of one electron = - 1)3.1. Determine the nuclear charge of calcium atom3.2.Calcium atom looses 2 electrons and becomes Ca2+. Traduce this statement into an equation.3.3.Justify by calculation the total charge of calcium ion.
Exercise 9: Sulfur
Sulfur, constituting 0.5% of our blood, is an indispensable non-metal thatensures metabolismreactions. Remember that certain alkali-metals: Sodium, Potassium, and Calcium produce bases (antiacids) in presence of water and sulfur. One of the most important roles of sulfur is to ensure the acid-basebalance in our body especially in the cerebral fluid, amniotic fluid and the bone metabolism.
1.The atom of sulfur has 6 valence electrons that occupy 3 energy levels.
1.1. Write the electronic configuration of sulfur.1.2. Deduce the Lewis dot symbol.
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1.3. Determine the relative charge of the electronic cloud of sulfur atom.(Relative charge of an electron = -1)
2.Potassium of atomic number Z = 19 is found in nature as a mixture of three atoms.The relative abundanceof this variety of atoms is indicated in the following table :
Mass number (A) 39 40 41
Relative abundance 83 % 10 2%
2.1. What can we call these three atoms? Justify.2.2. Compare the composition of the nuclei of these three atoms of potassium.2.3. Write the electron configuration of potassium atom.
3.Sulfur combines with hydrogen to form hydrogen sulfide H2S by a single covalent bond, while it formsK2S with potassium by an ionic bond.
3.1.Give the Lewis representation of H2S molecule. ( H an 1 valence electron).3.2.Distinguish between the formation of ionic and covalent bond.
4.State, referring to the text, the fundamental roles of sulfur.
Exercise10 Reactivity of metals
The metals are used daily for a long time. Metals are: conductors of electricity and heat, smoothed andpolished, they have a metallic shine, opaque, shock resistant, malleable, oxidized, and can be attacked byacids.To compare the reactivity of certain metals (Cu, Zn and Ag) the three experiments is carried out.
Experiment n° 1 Experiment n° 2 Experiment n° 3
After a longer period, it still doesnot appear blue precipitate. Thenno reaction.
The copper metal is appeared andthe solution is colorless(appearance Zn2+ ion).
Galvanic Cell (G).
1.The equation of the reaction in experiment No. 2 is: Cu 2+ + Zn Zn2+ + Cu shows that zinc have agreater tendency to lose electrons than copper.1.1.Show, using oxidation numbers, that the above reaction is a redox reaction.1.2.Specify the species which undergoes oxidation.
2.When the electrochemical cell (G) is operated, and during the reaction, the amount of positive charges incopper (II) ions Cu2+ increases and the amount of positive charges silver ions Ag+ decreases. Thecathode of this battery is the plate of silver.2.1.Justify that the cathode of this battery is the silver plate.
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2.2.Write electronic half equation for the cathode and the electron half equation to the anode of thiselectrochemical cell.
2.3.Deduce the chemical equation of the reaction that occurred.2.4.Give the written representation of this cell
3.Verify that the lamp lights up when the student of grade 9, connects the two solutions by electric copperwire in place of the salt bridge and closes the switch.
4.Sort the metals: Ag, Zn and Cu on an axis according to their increasing tendency to lose electrons.Exercise11 : Function of electrochemical cell
The oxidation-reduction in an electrochemical cell is a spontaneous reaction that produces electricity.Electrical energy is produced when the oxidation and reduction occur in separate containers connected by adevice that allows electrons to flow.
The schemas (I) and (II), given below, represents Zinc-copper electrochemical cell:
1.Compare the two given schemas.2. The electrochemical cell is working:
2.1. Show that the anode of this cell is the zinc strip. 2.2. Write half-equation at the cathode and the half equation at the anode of the electrochemical cell.
2.3. Deduce the overall equation of this cell.2.4. Give the schematic representation of this cell.
3. The salt bridge of a galvanic cell (G3) contains jellified potassium chloride (K+, Cl-)Given: K: K2 L8 M8 N1` and Cl : K2 L8 M7
3.1. Identify the type of bond in potassium chloride.3.2. Explain why K+ and Cl- ions of the salt bridge move simultaneously and respectively towards the
solution of the cathodic half cell and move toward the solution of the anodic half-cell of theelectrochemical cell.4. Specify if the lamp lights when a student of Grade 9, connects the two solutions in the scheme (I) by anelectric copper wire in place of the salt bridge and closes the switch.
Exercise12 Metals classification in galvanic cells.
A student wants to classify the following metals: Zn, Ag and Fe in increasing order of their tendency of
losing electrons. For this reason , he performs the following experiments. Given the half galvanic cells (I),
(II) et (III) :
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1. An electrochemical cell (G1) is constructed by associating the half cell (I) and the half cell (II). The
equation of the reaction is: Zn + Fe2+ Zn2+ + Fe
1.1.Using oxidation numbers , show that this reaction is a redox reaction.
1.2.Identify the anode and the cathode of (G1)
2. A galvanic cell (G1) is constructed when half-cell (I) is associated to half-cell (III) it is representedas Fe|Fe2+ || Ag+| Ag.
2.1.Write the half equations that take place on each electrode.
2.2.Deduce the overall equation.
3. A galvanic cell (G3) is constructed by associating half-cell (II) to half-cell (II). We remark that themass of zinc strip decreases.
3.1.Draw a labeled schema of this cell.
3.2.Give the schematic representation of this cell
4. Basing on the results, classify these Zn, Ag and Fe elements on the axis.
.
Exercise13 Voltage of an electrochemical cell and metals selected
A group of students used the materials indicated below to build two electrochemical cells P1 and P2.Data: In an electrochemical cell, the greater the difference in the tendency to lose electrons of metals usedas electrodes, the greater the voltage (voltage) of the electrochemical cell is large.Material:
Strips: Silver, zinc and aluminum.Solutions: aluminum nitrate (Al3+ + 3NO3
-), silver nitrate (Ag++ NO3-), zinc nitrate (Zn2++ 2NO3
-).Salt bridges, connection wires, voltmeters and beakers.
The pattern of each of the two electrochemical cells (P1) and (P2) is shown below:
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1. Name the equipment numbered in the diagram of the electrochemical cell (P1) and in the schema of theelectrochemical cell (P2).2. Referring to the stack (P1): 2.1. Explain why aluminum strip becomes thinner when the battery runs for a while.
2.2. Choose from the following symbolic representations that corresponding to the stack: a) Zn | Zn2+ ― pont salin ― Al3+| Al b) Al | Al3+ ― pont salin ― Zn | Zn2+
c) Al| Al3+ ― pont salin ― Zn2+| Zn
3. Referring to the stack (P2):3.1. Identify the cathode of the cell and write the half - reaction equation held.3.2. Write the oxidation half equation.3.3. Deduce the overall equation for the reaction.4. Based on the foregoing. Rank the three metals Al, Zn and Ag on a horizontal axis in ascendingorder of their tendency to lose electrons.5. We construct an electrochemical cell (P3) following symbolic representation:Zn | Zn2+ ― pont salin ― Ag+| Ag
Specify which of the following voltages: (3.36 V, 0.5 V; 1.56 V), which may be associated with theelectrochemical cell (P3).
Exercise14 The hydrocarbons
The aliphatic hydrocarbons can be alkanes, alkenes or alkynes Consider the molecular model of three hydrocarbons (A), (B) and (C).
(C)(B)(A)
Given:
1. Justify why the above compounds are hydrocarbons.
Hydrogen Carbon
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2. Reproduce and complete the following table:Compound A B C
Family
Name
3. The Compound (B) is a very interesting reactant in organic synthesis. This compound reacts with waterto give a compound (D).3.1. Write, using condensed structural formulas of the organic compounds, the equation of the reactionbetween the compound (B) and water.3.2. Specify the type of the reaction (addition or substitution).
4. The butane is used as the "essence" lighter, it hastwo isomers.4.1. Give the name of each of the isomers.
4.2. Distinguish the non-branches alkane from thebranched alkane.
Exercise15 Importance of crude oilCrude oil is an important natural resource. After oil refining, the derivatives obtained are used in thepreparation of several chemicals. Some of these derivatives are used in plastics manufacturing, while othersare used as an important source of energy.At the refinery, the crude oil is subjected to fractional distillation and the alkanes obtained with a longcarbon chain are still subjected to cracking.
1- Distinguish between fractional distillation and cracking.2- Alkane of molecular formula C5H12 , admits three isomers. The condensed structural formula of two
isomers is given:
2.1.Write the condensed structural formula of the third isomer (III).2.2.Give the name of each of the three
isomers.2.3.The following table shows the
boiling point of the three isomers.
2.3.1. Deduce how does the boiling point vary according to the number of ramifications in the isomersmolecule.
2.3.2. Indicate the physical state of the isomer (II) at 25°C at 1 atmosphere.
2- At the refinery, the cracking of heptanes produces an alkane (A) of linear chain containing 4 carbonatoms and an alkene (B) of molecular formula CxHy. C7H16 (A) + CXHY
2.1.Show that the molecular formula of hydrocarbon (A) is C4H10 .2.2.Determine the molecular formula of (B).2.3.Write the condensed structural formula of (B)
Non-branched alkane Branched alkane
Hydrocarbon (I) (II) (III)
Boiling point (°C) 36 28 10
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3- The addition polymerization of (B) produces a polymer (P). A portion of polymer (P) is represented:3.1. Give the name of this polymer.3.2. Give the number of repetitive unit in the portion ofpolymer (P) given before.4. Give two reasons why crude oil is consideredimportant natural resource.
Exercise16 Organic raw materials
Alkenes are unsaturated hydrocarbons. A molecule of an alkene has a double covalent bond betweentwo consecutive atoms of carbon.1. To identify ethene which is an alkene, we use a solution of bromine of orange color. The ethene reactswith bromine (Br2) to give an organic compound (A).
1.1. Indicate how color varies from orange after reaction.1.2. Identify which of the following semi-developed formulas do not correspond to the compound (A)
a) CH2BrــــCHBrــــCH3 b) CH2Br2 c) CH2BrـــــCH2Br
2. Propene is produced from cutting "naphtha" of petroleum hydrocarbons. The cut "naphtha" isheated away from air and the following reaction takes place according to the equation:
C10H22 2 C3H6 + CxHy(A)2.1. Give the name of the technique used for cutting "naphtha" from oil and the name of the technique usedfor having propene from the cup "naphtha".2.2. Indicate the difference between two techniques.2.3. Determine the molecular formula of the compound (A) and give its name.
3. Several synthetic polymers are formed of a single type of monomer, and are called homopolymers. Thepolymerization of propene produced the polypropylene polymer is not biodegradable. The polypropyleneis used to prepare bottles, cans, garbage ......3.1. Write the equation of the polyaddition reaction.3.2. Justify that polypropylene is a homopolymer.
Exercise 17 Fossil Fuel and Air Pollution
The figure given shows some pollutants released by burning fossilfuels. Some of these pollutants come from impurities in fuel orfrom lead compounds that are added to certain fuels. The fuel usedin car engines contains hydrocarbons among which is ahydrocarbon (A) of formula C 8 H 1 8 .
1. Show that the hydrocarbon (A) is an alkane.2. Write the names and formulas of two products, which are not
shown in the figure that form during the complete combustionof hydrocarbon (A).
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3. Give the names of two gases emitted from car exhaust, one leading to the formation of acid rain and theother contributing to the greenhouse effect.
4. Explain, why using fuel having low sulphur content contribute to reduce the formation of acid rain.
Exercise 18 Chlorofluorocarbons and the Ozone Layer
Certain ultraviolet rays coming from the sun are harmful. The exposure of human to these ultraviolet rays,causes sunburn, skin cancer, cataracts,...The ozone layer in the upper level of the atmosphere (stratosphere)prevents a large part of these ultraviolet rays to reach the Earth’s surface..In 1984, a big hole wasdiscovered in the ozone layer above the South Pole. This hole has been attributed to the presence of largeamounts of chlorofluorcarbons (CFC)s in the atmosphere, such as CFC1 3 , C 2 F 4 Cl2 ,... These compoundsare fluids largely used in aerosols, refrigerators, air conditioning systems,... (CFC)s are actually replaced byfluids, less harmful for the ozone layer, such as the hydrofluorocarbons (HFC)s.One example of these replacement products is H 2 FC – CF 3 .
Given: The electron-dot symbol of the elements carbon, fluorine and chlorine are respectively:
1. Write the Lewis dot structure for the molecule of CFC1 3
2. Indicate the type of the bond between the carbon atom and the fluorine atom in the CFC1 3
molecule. Justify.
3. Write the structural formula of H 2 FC – CF 3 .
4. Refer to the passage and answer the following questions:
4.1.Specify due to what is the hole in the ozone layer.
4.2.Indicate the role of the ozone layer.
4.3.Give two harmful effects caused by the exposure to the ultraviolet rays.
4.4.Suggest a way to protect the ozone layer.
Exercise 19 Sulfur Dioxide and Acid Rain
The graph given below shows the averageamount of sulfur dioxide SO2 gas emittedinto the air from the combustion of fuelcontaining sulfur as impurity. SO2 gascontributes to the formation of acid rain.The maximum tolerable level of SO2 inair is 75 g /m3.Combustion of sulfur to sulfur dioxideoccurs according to the equation: S +
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O2 SO2 (E1)SO2 changes in the air to sulfur trioxide SO3 according to the equation: 2SO2 + O2 2 SO3 (E2)In the clouds and in the presence of humidity, SO3 forms sulfuric acid H2SO4 according to the equation:
SO3 + H2O H2SO4 (E3) .
1- Calculate the oxidation number of sulfur in each of the following compounds : SO2 , SO3 and H2SO4 .
2- Using oxidation number :
2.1. Show that the reaction represented by equation (E3) is not an oxidation-reduction reaction.
2.2. Specify whether sulfur is reduced or oxidized in the oxidation-reduction reaction represented by
equation (E1).
3- Indicate and justify during which months air is polluted due to sulfur dioxide emission.
