fakta kimia spm 2015
DESCRIPTION
FactsTRANSCRIPT
1
1. Define atoms, molecules and ions, • An atom is the neutral particle of an element that can take part in a
chemical reaction.
• A molecule is a neutral particle consist of a group of two or more
atoms which are chemically bonded together.
• An ion is a positively charged or negatively–charged particle.
2. Draw the arrangement of particles
Solid liquid Gas
3. The movement of bromine particles in
air
• The bromine molecules are made of tiny and discrete molecules.
that move randomly and collide each other and with other particles
in air to fill up space.
• The molecules moves randomly and diffuses in all direction in air
from area of higher concentration to area of lower concentration.
• The bromine molecules spreads throughout both gas jar
4. What is melting point? • Melting point is the temperature at which the substance at its solid
state changes to liquid state at certain pressure.
5. Explain why the temperature remains
unchanged during the melting process.
• Heat energy absorbed by the particles is used to overcome the
forces of attraction between the molecules so that the solid can turn
into liquid.
6. Explain why the temperature remains
unchanged during the freezing process.
• The heat lost to the surroundings is exactly balanced by the heat
energy given out / released as the molecules attracted one another
to form solid.
7. State the main subatomic particles of an
atom.
• An atom contains three types of subatomic particles; proton, neutron
and electron.
2 8. Compare and contrast the relative
atomic mass and the relative charge of
the subatomic particles of the atom.
Subatomic
particle Symbol
Relative
mass
Relative
charge
Proton p 1 +1
Electron e 1/1840 -1
Neutron n 1 Neutral
9. State the meaning of proton number and
nucleon number
• Proton number of an element is the number of proton in its atom.
• Nucleon number of an element is the total number of proton and
neutron in its atom.
10. State the meaning of isotopes. • Isotopes are atoms of the same element with the same number of
proton but different number of neutron. //
• Isotopes are atoms of the same element with the same proton
number but different nucleon number.
11. State the chemical and physical
properties of isotopes
• The isotopes of an element have the same chemical properties
because they have the same number of electrons and the same
electron arrangement.
• The isotopes of an element have the different physical properties
because they are different in nucleon number.
12. State the meaning of empirical
formula.
• Empirical formula is the formula that shows the simplest whole
number ratio of atoms of each element in the compound.
13. State the meaning of molecular
formula.
• Molecular formula is the formula that shows the actual number of
atoms of each element that are present in a molecule of the
compound.
14. Why was the crucible lid opened once
in a while during the experiment?
15. State how to determine that the
reaction between magnesium and
oxygen has completed.
• To allow oxygen from the air to react with magnesium.
• Repeat the heating, cooling and weighing process until a constant
mass is obtained.
16. Suggest a suitable chemical
substance for X in Part B and state the
function of X.
17. Why is hydrogen gas passed through
the combustion tube after heating has
stopped?
• Substance X : Anhydrous calcium chloride
Function : To dry the hydrogen gas
• To prevent copper metal react with oxygen gas from surrounding to
form copper (II) oxide again //
To avoid the oxidation of copper//
To avoid the formation of copper (II) oxide.
18. Why the method to determine the
empirical formula of copper(Il) oxide
cannot be used to determine the
empirical formula for magnesium
oxide?
• Magnesium is more reactive than hydrogen.
Hydrogen gas cannot reduce magnesium oxide to magnesium.
3 19. Why the method to determine the
empirical formula of magnesium oxide
cannot be used to determine the
empirical formula for copper(Il) oxide?
• Because copper is not a reactive metal.
It reacts slowly with oxygen. Therefore, it is difficult to convert copper
to copper(II) oxide completely.
20. What is the meaning of the “period” in
the Periodic Table of element?
A horizontal row of elements in the Periodic Table of Element.
21. What is the meaning of the “group” in
the Periodic Table of element?
A vertical column of elements in the Periodic Table of Element.
22. State the position of element, !"#$%
in
Periodic table of Elements. Explain
your answer
• Electron arrangement of X atom is 2.8.8.2
• X atom has 2 valence electrons. Therefore, it is in Group 2.
• X atom has 4 shells occupied with electrons Therefore, it is in Period
4.
23. Why helium gas is not reactive
chemically?
• Helium has 2 valence electrons. This is stable duplet electron
arrangement.
• It does not need to gain, lose or share electrons with other atom of
elements.
24. Explain why argon does not react with
hot tungsten filament in term of
electron arrangement.
• Argon atom has attained octet electron arrangement//
Argon atom has 8 valence electrons//
Argon atom’s outermost shell is completely filled with electrons.
• This electron arrangement is stable //
Argon is inert / unreactive.
• Argon atom does not need to gain, lose or share electrons with
other elements. 25. Why the melting point and boiling
point increase when going down
Group 18
• the atomic size of the elements increase down the group
• the attraction force between atoms of each element become
stronger.
• Thus more heat energy required to overcome the stronger forces of
attraction.
26. Why helium gas is more suitable to fill
weather balloon compared to
hydrogen gas?
• Because helium gas is lighter and not flammable and hydrogen is
flammable
27. State the physical properties of Group
1.
• Alkali metals are good conductors of heat and electricity.
• They are soft and can be cut easily with a knife.
• All alkali metals are grey in colour with silvery and shiny surfaces
when freshly cut.
• They have relatively low melting and boiling points compare to other
metals such as iron (MP : 1540°C).
• There have low densities end float on surface of water.
28. Why the melting point and boiling
point decrease when going down
Group 1
• The atomic size of the elements increase down the group.
• the attraction force between atom of each element become
weaker.
• Thus less heat energy required to overcome the weaker forces of
attraction
29. Why all alkaline metal can conduct
electricity
Each atom has one electron valence that act as free moving electron
30. The reactivity of Group 1 increases
when going down the group. Explain
why.
• When going down Group 1, proton number of elements is increase.
• The atomic size increases.
• The single valence electron becomes further away from the nucleus.
• Hence, the force of attraction between the nucleus and the valence
electron becomes weaker.
• As a result, it is easier for the atom to lose the single valence
electron to achieve the octet or duplet electron arrangement.
31. Potassium reacts more vigorously with
water as compared to sodium. Explain.
(Proton number: Na, 11 ; K, 19)
• Force of attraction between the nucleus and the valence electron
for potassium is weaker then sodium.
• Therefore it is easier for potassium atom to donate the single
valance electron than sodium atom.
4 32. Sodium burnt in oxygen and the
product is dissolved in water. What is
the property of the solution formed?
Explain why.
• The solution is an alkaline solution.
• Sodium burns in oxygen to produce sodium oxide. Sodium oxide
dissolves in water to produce sodium hydroxide solution.
33. State the physical properties of Group
I7.
• Halogens exits as diatomic molecules.
• Halogens have low melting and boiling points.
• They are good insulator of electricity.
• They are poor conductors of heat.
34. State the changes of the physical
properties of Group 17 when going
down the group.
• The physical state of halogens at room temperature changes from
gas to liquid, then to solid.
• The colour of halogen becomes darker.
35. The reactivity of Group 17 decreases
when going down the group. Explain
why
When going down Group 17,
• The atomic size increases.
• The outermost occupied shell of each halogen atom becomes further
away from the nucleus.
• Thus, the force of attraction between the nucleus and electrons
become weaker.
• As a result it is more difficult to attract one electron into the
outermost occupied shell.
36. Chlorine gas is dissolved in water.
What can you observe if a piece of
blue litmus paper is immersed into the
solution formed? Explain why.
• Blue litmus paper turns red and then bleached.
• When chlorine gas dissolves in cold water, it forms hydrochloric acid,
HCI and hypochlorous acid, HOCl.
• Hydrochloric is an acid which tums blue litmus paper red while
hypochlorous acid is a strong bleaching agent which decolourise the
litmus paper.
37. State four special properties of
transition elements.
• Transition elements form coloured solutions or compounds.
• Transition elements show different oxidation number in their
compounds.
• Transition elements act as catalysts in certain chemical reactions.
• Transition elements can form complex ions.
38. When across Period 3 from sodium to
argon, the atomic size decreases.
Explain why.
When across Period 3 from left to right;
• The number of protons in the nucleus increases. This increases the
positive charge of the nucleus.
• As a result, the attraction force between the nucleus and the
electrons becomes stronger.
• Electrons are pulled closer to the nucleus, causing the atomic size
to decrease.
39. When across Period 3 from sodium to
argon, the electronegativity increases.
Explain why.
When across Period 3 from left to right.
• The atomic size decreases
• The number of protons in the nucleus increases. This increase the
positive charge of the nucleus
• As a result the attraction forces between the nucleus and the
electrons in the outermost shell becomes stronger
• This increases the increase the tendency to attract electrons
across the period.
• Therefore, electronegativity increases.
40. State two physical properties of ionic
compounds.
• High melting point and boiling point
• Conduct electricity in aqueous solution molten state.
• Usually dissolve in water
• Do not dissolve in organic solvent.
41. State two physical properties of covalent
compounds.
• Low melting point and boiling point.
• Do not conduct electricity in any state.
• Usually dissolve in organic solvents such as benzene
• Do not dissolve in water.
5 42. Explain why covalent compound do not
conduct electricity in all states.
• Covalent compound do not conduct electricity in all state because
they consist of neutral molecules.
• There are no freely moving ions.
43. Explain why ionic compounds are able to
conduct electricity in aqueous solution or
in molten state but not in solid state.
• Ionic compounds can conduct electricity in aqueous solution or in
molten state because the charged ions can move freely and randomly.
• Ionic compound in solid state cannot conduct electricity because the
ions are held together by the strong electrostatic forces in the lattice
structure and are not freely and randomly move
44. Why ionic compound has high melting
point and boiling point
• In ionic compounds, the oppositely charged ions are held together by
a strong electrostatic forces.
• Higher amount of heat energy is needed to overcome the forces.
45. Why covalent compound has low melting
point and boiling point
• In covalent compound, the attraction forces between molecules are
weak.
• Lower amount of heat energy is needed to overcome the forces.
46. Magnesium chloride and hydrogen
chloride are two compounds of chlorine.
At room condition, magnesium chloride
exists as a solid but hydrogen chloride
exists as a gas. Explain why.
• Magnesium chloride is an ionic compound whereas hydrogen chloride
is a covalent compound.
• Magnesium ion and chloride ions are held together by strong
electrostatic forces of attraction. Therefore, it has very high melting
point and boiling point and exists as solid at room condition.
• Hydrogen chloride consists of molecules. The intermolecular force
between the molecules is week. Therefore, it has low melting point
and boiling point and exists as gas at room condition.
47. Explain the formation of ionic bond
between sodium atom, &'(("$
and chlorine
atom, )*(+$,
• Electron arrangement of sodium atom is 2.8.1
• A sodium atom donate/release/lose one electron to achieve the
stable electron arrangement which is 2.8.
• Sodium ion, Na+ is formed.
• Half equation : Na à Na+ + e
• Electron arrangement of chlorine atom is 2.8.7
• Electron from sodium atom is transferred to a chlorine atom
• A chlorine atom accept/receive/gain electron from sodium atom to
achieve the stable electron arrangement which is 2.8.8.
• Chloride ion, Cl- is formed.
• Half equation : Cl + e à Cl-
• The sodium ion, Na+ and chloride ion, Cl
- formed are attracted to one
another to form an ionic compound sodium chloride, NaCl.
• The strong attraction forces between the opposite-charged ions is
called ionic bond.
48. Explain the formation of covalent bond
between carbon atom, )-(" and chlorine
atom, )*(+$,
.
• Carbon atom has electron arrangement of 2.4
• Chlorine atom has electron arrangement of 2.8.7
• One carbon atom contributes 4 valence electrons to four chlorine
atoms.
• Four chlorine atoms contribute 1 valence electron each to carbon
atom.
• Carbon atom shares 4 pairs of electrons with 4 chlorine atoms to
form 4 single covalent bonds.
• All of Carbon and Chlorine atoms achieve stable octet electron
arrangement.
• A covalent compound with formula CCI4 is formed.
6 49. To compare the characteristics for the
formation of ionic and covalent bonds.
Ionic bond Characteristic Covalent bond
Valence electrons Electrons involved Valence electrons
Metal atoms and non
metal atoms Elements
Non-metals atom and
non metal atoms
Electron transfer to
achieve stable
electron arrangement
Bond formation
Sharing electron to
achieve stable
electron arrangement
Ions Particles Molecules
50. State the meaning of electrolyte. • Electrolyte is the substance that can conduct electricity in molten or
aqueous state and undergo chemical change.
51. State the meaning of electrolysis • Electrolysis is a process whereby compounds in molten or aqueous
states are broken down (or decomposed) into their constituent
elements by passing electricity through them.
52. State the energy change in electrolysis. • Energy change in electrolysis is electric energy to chemical energy
53.
Electrolysis of molten electrolyte Electrolysis of aqueous electrolyte (no
gas released)
Electrolysis of aqueous electrolyte
(gas is released)
54. Explain why solution of hydrogen chloride
in water can conduct electricity but
solution of hydrogen chloride in
methylbenzene cannot conduct
electricity?
• Hydrogen chloride is a covalent compound.
• In methylbenzene, hydrogen chloride exists as molecule. Therefore, it
cannot conduct electricity.
• In water, hydrogen chloride ionises to produce hydrogen ion and
chloride ion which are free to move.
• Therefore, it can conduct electricity.
55. Explain how copper electrodes affect the
selective discharge of ions at the anode
during electrolysis of copper(ll) sulphate
solution.
• When electrolyse copperl(ll) sulphate solution using copper electrodes,
no ion is discharged at anode.
• Instead, the copper anode itself dissolves to form copper(ll) ions.
Cu ⎯→ Cu2+
+ 2e
56. Explain how concentration of ions in
electrolyte affects the selective discharge
of ions at the anode during electrolysis of
hydrochloric acid.
• When using dilute hydrochloric acid (0.0001 mol dm-3
), hydroxide ion is
discharged at anode to produce oxygen gas.
4 OH- ⎯→ 2 H2O + O2 + 4e
• When using concentrated hydrochloric acid (1.0 mol dm-3
), chloride ion
is discharged at anode to produce chlorine gas.
2 Cl- ⎯→ Cl2 + 2e
57. Explain why the blue copper(ll) sulphate
solution remains unchanged when
copper is used as electrodes.
• The rate of the discharged of copper(ll) ions at the cathode is the same
as the rate of ionisation of copper anode. The concentration of
copper(ll) ions remains unchanged.//
• The copper(ll) ions discharged at the cathode is replaced with the
copper(Il) ion formed from the anode. The concentration of copper(ll)
ions remains unchanged.
58. Explain the process of electrolysis of
sodium nitrate solution using carbon
electrode
• Sodium nitrate solution consists of Na+, NO3
-, H
+, and OH
- ions.
• During electrolysis, Na+
and H+ ions move to cathode and NO3
- and
OH- ions move to anode.
• At cathode, H+ ion is selectively discharged because it is lower than
Na+ ion in electrochemical series.
• Hydrogen gas is given out at cathode.
• At anode, OH- ion is selectively discharged because it is lower than
NO3
- ion in electrochemical series.
• Oxygen gas is given out at anode.
7 59. Explain how Daniell Cell can generate
electricity.
• In Daniell Cell, zinc is more electropositive than copper.
• Zinc acts as the negative terminal and copper acts as the positive
terminal.
• Zinc donates electrons to form zinc ions, Zn2+
.
• Electrons flow from zinc electrode to copper electrode through the
external circuit.
• At copper electrode, electrons are received by the copper(Il) ions, Cu2+
in the copper(II) sulphate solution to form copper atoms.
• The continuous flow of electrons from zinc electrode to copper
electrode produces electric current in the Daniell Cell.
60. What is the meaning of strong acid and
weak acid
• Strong acid is an acid that ionizes completely in water to produce
high concentration of hydrogen ions, H+
and had a lower pH value.
Example : Hydrochloric acid, nitric acid and sulphuric acid
• Weak acid is an acid that ionizes partially in water to produce low
concentration of hydrogen ions, H+ and had a higher pH value
• Example : Ethanoic acid
61. What is the meaning of strong alkali and
weak alkali.
• Strong alkali is an alkali that ionizes completely in water to produce
high concentration of hydroxide ions, OH- and had a higher pH value
Example : Sodium hydroxide, potassium hydroxide
• Weak alkali is an alkali that ionizes partially in water to produce low
concentration of hydroxide ions, OH- and had a lower pH value.
Example : Aqueous ammonia
62. What is neutralisation? • Neutralisation is a reaction between an acid and a base / alkali to
produce salt and water only
63. The pH value of glacial ethanoic acid is 7
but the pH value of dilute ethanoic acid is
5. Explain why the pH values of the two
substances are different
Glacial ethanoic acid molecule does not ionize and consists of only
neutral CH3COOH molecule. Glacial ethanoic acid does not have
hydrogen ion.
Ethanoic acid solution is a weak acid which ionizes partially in water to
produce a lower concentration of hydrogen ions and ethanoate ions.
CH3COOH � CH3COO- + H
+
The presence of hydrogen ions causes ethanoic acid solution to have
acidic properties
Glacial ethanoic acid has a pH value of 7 and the pH value of ethanoic
acid solution is less than 7
64. Explain why sulphuric acid and
hydrochloric acid have different pH value.
Sulphuric acid is a diprotic acid which 1 mol of acid ionizes completely in
water and produce 2 mol of hydrogen ions.
H2SO4 à 2H+ + SO4
2-
Hydrochloric acid is a monoprotic acid which 1 mol of acid ionizes
completely in water to produce 1 mol of hydrogen ions.
HCl à H+ + Cl
-
The concentration of hydrogen ions in sulphuric acid is higher than the
concentration of hydrogen ion in hydrochloric acid.
The pH value of sulphuric acid is lower than the pH value of hydrochloric
acid
65. The pH value of solution ammonia in
water is 9 but the pH value of solution of
ammonia in trichloromethane is 7.
Explain why the pH values of the two
solutions are different.
• Dry ammonia gas (or ammonia gas) dissolved in trichloromethane
consists of neutral molecules, NH3 only.
• There is no hydroxide ions, OH-. Therefore, it does not show alkaline
property.
• In water, the NH3 molecules will ionise to produce hydroxide ions, OH-.
• The presence of hydroxide ions, OH- will cause the aqueous ammonia
solution to show alkaline properties.
66. The pH values of 1.0 mol dm-3
of
ethanoic acid and 1.0 mol dm-3
hydrochloric acid is 4 and 1 respectively.
Explain the differences.
Hydrochloric acid is a strong acid which ionizes completely in water to
produce a higher concentration of hydrogen ion.
HCl à H+ + Cl
-
Ethanoic acid is a weak acid which ionizes partially in water to produce a
lower concentration of hydrogen ions.
CH3COOH � CH3COO- + H
+
The concentration of hydrogen ions in hydrochloric acid is higher than
the concentration of hydrogen ion in ethanoic acid.
The pH value of hydrochloric acid is lower than the pH value of ethanoic
acid
8 67. Given dilute nitric acid and dilute
sulphuric acid have the same
concentration of 0.5 mol dm-3
. In a
neutralisation experiment, 20 cm3 of nitric
acid is required to neutralise 20 cm3 of
sodium hydroxide solution but only 10
cm3 of sulphuric acid is required to
neutralise 20 cm3 of sodium hydroxide
solution. Explain why.
• Nitric acid is a monoprotic acid whereas sulphuric acid is a diprotic
acid.
• The concentration of hydrogen ions in sulphuric acid is double than that
in nitric acid.
• As a result, the volume of sulphuric acid required is half compared to
nitric acid.
Preparation of standard solution using the exact mass of a solute
(a) Calculate the mass of solute needed to give the required
volume and mass.
Weigh out the exact mass of solute needed in a weighing
bottle.
Dissolved the solute completely in little distilled water in a
beaker
(b) Transfer the dissolved solute into a suitable volumetric
flask.
Wash and rinse the weighing bottle, small beaker and filter
funnel to ensure no solute remains in any of the apparatus
used.
(c) Add more distilled water carefully to the volumetric flask
and swirl gently.
Shake well to ensure thorough mixing.
(d) Add distilled water slowly by using a dropper to bring the
level of the solution to the calibration mark.
The volumetric flask is closed tightly and inverted several
times to get a uniform or homogenous solution.
Preparation of standard solution using dilution method
(i) Quantity that are needed
(a) the volume and concentration of the stock solution
(b) the volume of the new solution
(ii) Adding water to the standard solution lowered the concentration of the solution. Since no solute is added, the
quantities of solute in the solution before and after dilution remain unchanged.
Number of mole of solute before dilution = Number of mole of solute after dilution
M1V1 = M2V2
M1 = molarity of solution before dilution
V1 = volume of solution before dilution
M2 = molarity of solution after dilution
V2 = volume of solution after dilution
9 (iii) steps involved
Calculate the volume of stock solution required by using the equation :
M1V1 = M2V2
When using this equation, make sure that both V1 and V2 are of the same unit.
Use a pipette to draw up the required volume of stock solution.
Transfer the stock solution to a suitable volumetric flask.
Add water slowly by using a dropper to bring the level of the solution to the
calibration mark.
The volumetric flask is closed tightly and inverted several times to get a uniform or
homogenous solution.
68. What is salt? • A salt is a compound formed when the hydrogen ion, H+ from an acid is
replaced by a metal ion or an ammonium ion, NH4
+.
69. Solubility of salts in water All sodium, potassium and ammonium salts are soluble in water.
All nitrate salts are soluble in water.
All sulphate salts are soluble in water except calcium sulphate, lead (II)
sulphate and barium sulphate.
All chloride salts are soluble in water except silver chloride , lead (II)
chloride and mercury (I) chloride.
All carbonate salts are insoluble in water except sodium carbonate,
potassium carbonate and ammonium carbonate
70. Method used to prepare salt depend on
the solubility of the salt
a. Soluble salts are prepared from the reactions between an acid with
metal, base, alkali and metal carbonate.
i. metal + acid à salt + hydrogen
ii. metal oxide (or metal hydroxide) + acid à salt + water
iii. alkali + acid à salt + water
iv. metal carbonate + acid à salt + carbon dioxide + water
b. Insoluble salts are prepared by the precipitation method through a
double decomposition reactions.
i. In this reaction, the precipitate of insoluble salt is formed when
two different solutions that contains the cation and anion of the
insoluble salt are mixed.
ii. The insoluble salt is obtained as a residue of a filtration
10 The preparation of soluble salts of sodium, potassium and ammonium
Soluble salt Sodium Chloride, NaCl
Name two chemical
substances to prepare the
salt
1. sodium hydroxide
2. hydrochloric acid
List of apparatus and
material
1. burette
2. retort stand
3. conical flask
4. Bunsen burner
5. Filter funnel
6. Spatula
7. Filter paper
8. Distilled water
9. Beaker
Chemical equation NaOH + HCl à NaCl + H2O
Procedure: (Diagram) Description
1. A pipette is used to transfer 25.0 cm3 of sodium hydroxide solution to a conical
flask. 2 to 3 drops of phenolphthalein is added.
2. A burette is filled with hydrochloric acid and record the initial burette reading.
3. Titration is carried out carefully by slowly adding the acid into the conical flask
and the flask is shaken well.
4. The acid is added continuously until the indicator turns from pink to colourless.
The final burette reading is recorded.
5. The volume of acid used to neutralize 25.0 cm3 of the alkali is determined. (let
the volume be V cm3 )
6. 25.0 cm3 of the same sodium hydroxide solution is pipetted into a conical flask.
No indicator is addeded.
7. From the burette, exactly V cm3 of hydrochloric acid is added to the alkali and
is shaken well.
8. The contents of the conical flask is poured into an evaporating dish.
9. The solution is heated gently to evaporate most of the water to produce a
saturated solution.
10. The hot saturated salt solution is cooled for crystallization to occur.
11. The sodium chloride crystals is filtered
12. The crystals are dried by pressing them between filter papers
11 The preparation of soluble salts (not sodium, potassium or ammonium salt)
Soluble salt Copper(II) sulphate, CuSO4
Name two chemical
substances to prepare
the salt
1. copper(II) oxide
2. sulphuric acid
List of apparatus and
material
1. Bunsen burner
2. Filter funnel
3. Spatula
4. Filter paper
5. Distilled water
6. Beaker
Chemical equation CuO + H2SO4 à CuSO4 + H2O
Procedure: (Diagram) Description
50 cm3 of sulphuric acid 1 mol dm
-3 is poured into a beaker. The acid is warmed.
By using a spatula, copper(II) oxide powder is added bit by bit into the acid. The mixture
is stirred well.
Copper(II) oxide is added continuously until some of it no longer dissolves.
The unreacted copper(II) oxide is removed by filtration
The filtrate is filtered into an evaporating dish.
The solution is heated gently to produce a saturated salt solution.
The saturated solution is cooled until crystals are formed.
The copper(II) sulphate crystals are filtered
The crystals are dried by pressing them between filter papers
12 The preparation of insoluble salts
Insoluble salt Lead(II) iodide, PbI2
Name two chemical
substances to prepare the
salt
1. lead(II) nitrate
2. Sodium/potassium iodide
Chemical equation Pb(NO3)2 (aq) + 2KI (aq) à PbI2 (s) + 2KNO3 (aq)
Ionic equation Pb2+
(aq) + 2I- (aq) à PbI2 (s)
Procedure: (Diagram) Description
50 cm3 of 0.5 mol dm
-3 lead(II) nitrate solution is poured into 50 cm
3 of 1.0 mol dm
-3
potassium iodide in a beaker
The mixture is stirred with a glass rod
A yellow precipitate of lead(II) iodide is formed immediately
The resulting mixture is then filtered
The yellow precipitate is rinsed with distilled water to remove impurities
The yellow solid, lead(II) iodide is then pressed between a few pieces of filter papers to
be dried
71. Describe a chemical test to identify the
presence of carbonate ions, CO3
2- in a
solution.
• 2 cm3 of the solution is poured into a test tube.
• 2 cm3 of dilute hydrochloric acid is added into the test tube
• The gas liberated is immediately bubbled / flown through lime water.
• The time water turns milky / chalky.
72. Describe a chemical test to identify the
presence of chloride ions, CI- in a
solution.
• 2 cm3 of the solution is poured into a test tube.
• 2 cm3 of dilute nitric acid is added into the test tube follow by about
2cm3 of silver nitrate solution.
• A white precipitate is formed.
73. Describe a chemical test to identify the
presence of sulphate ions, SO4
2- in a
solution.
• 2 cm3 of the solution is poured into a test tube.
• 2 cm3 of dilute hydrochloric acid is added into the test tube followed
by about 2 cm3 of barium chloride solution.
• A white precipitate is formed.
74. Describe a chemical test to identify the
presence of nitrate ions, NO3
-, in a
solution.
• 2 cm3 of the solution is poured into a test tube.
• 2 cm3 of dilute sulphuric acid is added into the test tube followed by 2
cm3 of iron(II) sulphate solution. The mixture Is shaken well.
• The test tube is slanted slightly. A few drops of concentrated
sulphuric acid are dropped carefully and slowly along the side of
slanting test tube into the mixture.
• A brown ring is formed.
13 75. Describe a chemical test to identity the
following ions
a) Copper(ll) ion, Cu2+
b) Magnesium ion, Mg2+
c) Zinc ion, Zn2+
(a) Copper(Il) ion
• Sodium hydroxide solution is added drop by drop until in excess. A
blue precipitate is formed and insoluble in excess sodium
hydroxide solution.
• Ammonia solution is added drop by drop until in excess. A blue
precipitate is formed and dissolves in excess ammonia solution
to produce a dark blue solution.
(b) Magnesium ion
• Sodium hydroxide solution is added drop by drop until in excess A
white precipitate is formed and insoluble in excess sodium
hydroxide solution.
• Ammonia solution is added drop by drop until in excess. A white
precipitate is formed and insoluble in excess ammonia solution.
(c) Zinc ion
• Sodium hydroxide solution is added drop by drop until in excess. A
white precipitate is formed and dissolves in excess sodium
hydroxide solution to form a colourless solution.
• Ammonia solution is added drop by drop until in excess. A white
precipitate is formed and dissolves in excess ammonia solution
to form a colourless solution.
Cation NaOH solution Ammonia Solution NH3
Ca2+
WPIS No change
Mg2+
WPIS WPIS
Zn2+
WPS WPS
Al 3+
WPS WPIS Pb
2+ WPS WPIS
Cu 2+
BPIS BPS
Fe 2+
GPIS GPIS
Fe 3+
BrPIS BrPIS
NH4
+ Ammonia gas released when heated No change
76. Describe a chemical test to identify the
following ions;
(a) iron(ll) ion, Fe2+
(b) iron(Ill) ion, Fe3+
(a) iron(II) ion
• 2 cm3 iron(II) chloride solution is poured into a test tube.
• Potassium hexacyanoferrate(III) solution is added into the test
tube.
• A dark blue precipitate is formed.
(b) iron (Ill) ion
• 2 cm3 iron(lll) chloride solution is poured into a test tube.
• Potassium thiocynate solution is added info the test tube.
• A red blood colouration is formed
77. Describe a chemical test to differentiate
the lead(Il) ion, Pb2+
and aluminium ion,
Al3+
.
• 5 cm3 of each solution is poured into two separated test tubes.
• Add 2 cm3 potassium iodide solution, KI into each of test tube.
• The solution in the test tube produce yellow precipitate consists of
lead(Il) ion.
78. Describe a chemical test to identify the
presence of ammonium ions, NH4
+ in a
solution
• 2 cm3 ammonia solution is poured into a test tube.
• Sodium hydroxide solution is added into the test tube
• The mixture is heated and a damp red litmus paper is placed near the
mouth of test tube.
• The damp red litmus paper turns blue.
79. What is the meaning of alloy? • Alloy is a mixture of two or more elements with a certain fixed
composition in which the major component is a metal.
80. State the aims of making alloys • Improve the appearance of the pure metal
• Improve the strength and hardness of the pure metal
• Increase the resistance to corrosion of the pure metal
81. Bronze is an alloy consists of copper
and tin. Explain why bronze is harder
than copper.
• Copper atoms in copper block are of the same sizes and arranged in
an orderly arrangement.
• The layers of copper atoms slide easily if force is applied.
14
• The copper atoms and the tin atoms are of different sizes.
• The presence of tin atoms disrupts the orderly arrangement of copper
atoms to bronze block.
• This reduces the layers of copper atoms from sliding over one another
easily.
82. What are raw materials used in Contact
process
Sulphur, air and water
83. State the optimum conditions for the
Contact process
• Catalyst - Vanadium(V) oxide, V2O5
• Temperature - 450°C
• Pressure - 1 atmosphere.
84. Explain the industrial process involved
in the manufacture of sulphuric acid
Write all the chemical equations
involved.
• Molten sulphur is burnt in excess air to produce sulphur dioxide gas.
S + O2 ⎯→ SO2
• Sulphur dioxide and excess oxygen gas are passed over vanadium(V)
oxide catalyst at 450°C and pressure of 1 atmosphere.
2 SO2 + O2 ⎯→ 2 SO3
• Sulphur trioxide is dissolved in concentrated sulphuric acid to form
oleum
SO3 + H2SO4 ⎯→ H2S2O7
• The oleum is then diluted in water to produce dilute sulphuric acid
H2S2O7 + H2O ⎯→ 2 H2SO4
85. Side effect of Sulphur dioxide • Sulphur dioxide gas from the burning of product manufactured from
sulphuric acid can cause lung disease and acid rain.
• Sulphur dioxide dissolves in rain water to form sulphurous acid
which will result in acid rain.
Chemical equation : SO2 + H2O à H2SO3
• Effects of acid rain:
(i) Acid rain corrodes building, monuments and statutes made of
marble (calcium carbonate) because calcium carbonate reacts with
acid to produce salt, water and carbon dioxide.
Chemical equation : CaCO3 + H2SO4 à CaCl2 + H2O +
CO2
(ii) Acid rain corrodes structure of building and bridges which are
made of metal. The iron from steel reacts with sulphuric acid to
form rust.
(iii) Acid rain increases the acidity of lakes and river causes the aquatic
organism to die
(iv) Acid rain increases the acidity of soil. Acidity soil is not suitable for
the growth of plants
86. Ways to reduce the production of
sulphur dioxide and effect of acid rain
• Gas released from power station, factories and vehicle are sprayed
with powdered calcium carbonate.
• Add calcium oxide and calcium carbonate to the lake and river
87. State the optimum conditions for the
Haber process
Equation: 3H2 + N2 à 2NH3
Raw material: hydrogen gas and nitrogen gas
• Catalyst - Iron filling
• Temperature - 450°C - 550°C
• Pressure - 200 atmospheres
88. Properties of ammonia 1. Colour: Ammonia is a colourless gas.
2. Solubility: Ammonia is very soluble in water.
3. Smell : Ammonia has a pungent smell.
4. Ammonia dissolves in water to produce an ammonium hydroxide
solution.
5. Turn red litmus paper to blue
6. Give a white fumes when reacted with hydrogen chloride gas
15 89. What is the meaning of polymers and
polymerization? Name the monomer of
polythene and polyvinyl chloride.
• Polymers are long chain molecules made up of many identical
repeating units called monomers.
• Polymerization is the process by which the large number of monomers
are joined together to form a big molecule known as the polymer.
• Ethene and chloroethene respectively.
90. Explain how synthetic polymers can
cause environmental pollution
• Non/not easily biodegradable
• Improper disposal can cause blockage of drainage//flash flood
• Improper disposal can cause eye sore
• Burning can cause acidic gas//poisonous gas//bad smell
• Burning can cause greenhouse effect//global warming/thinning the
ozone layer
91. Advantages of synthetic polymers • Very stable and do not corrode
• Inert to chemical reaction
• Light and strong
• Cheap
• Easily shaped and coloured
92. Environment pollution from synthetic
polymers
• Disposal of synthetic polymers such as plastic bottles and containers
cause blockage of drainage systems and rivers thus causing flash
floods
• Open burning of synthetic polymers will release acidic and
poisonous gas that cause air pollution.
• Burning of most of the synthetic polymers will produce :
i. Carbon dioxide which cause greenhouse effect
ii. Carbon monoxide which is poisonous
iii. Burning of PVC will release hydrogen chloride which will cause
acid rain
iv. Burning of synthetic polymers contains carbon and nitrogen
such as nylon will produce highly poisonous gas such as
hydrogen cyanide.
• Plastic containers that are left in open area collect rain water will
become breeding ground for mosquito which will cause diseases
such as dengue fever
93. Reducing pollution of synthetic
polymers
• Reduce, recycle and reuse the synthetic polymers
• Using biodegradable polymers
• On-going research to produce cheap biodegradable polymers.
• Disintegrate plastics by pyrolysis : plastics can be disintegrated by
heating at temperature between 400 – 800oC without oxygen.
94. Main component in glass • Main composition of glass is silicon dioxide, SiO2 which exist
naturally in sand
95. Properties of glass • transparent
• hard but brittle
• non porous
• heat insulator
• resistant to chemical
• easy to clean
• can withstand compression.
Composite material Composition Properties Uses
Reinforced concrete
Steel bars, polymer fibers
and concrete (cement, sand
and pebbles)
Very strong and can be moulded
into any shape
Construction of building,
bridges and oil platforms
Superconductors Barium carbonate, copper
(II) oxide and sodium oxide
heated to form a type of
ceramic known as
perovoskyte
Conducting electricity with no
resistance when it is cooled at
low temperature
Used in medical magnetic-
imaging devices(MRI),
generators, transformers,
computer parts and bullet
train
Fibre optic Silica, sodium carbonate,
calcium oxide
Low material costs,
High transmission capacity,
chemical stability,
Less susceptible to interference.
Transmit data, voice and
image in a digital format.
Fibre glass Polyester resin glass High tensile strength,
Easy to colour,
Low in density,
Very strong.
Photochromic glass Glass and silver chloride or
silver bromide
When it is exposed to light,
silver chloride is converted to
silver and darken the glass
16
1) What is rate of reaction? • Rate of reaction is the change In the quantity of the reactant or product
per unit time (general definition)
• Rate of reaction is the volume of carbon dioxide gas released per
second (specific)
2) What are observable changes to
reactants or products for determining
rate of reaction?
The amount of a reactant used up or a product obtained can be
measured in terms of
(a) changes in the mass or concentration of the reactant or product
(b) volume of gas produced
(c) changes in colour
(d) formation of precipitate
(e) changes in mass of the reaction mixture
3) State 2 different ways to measure the
rate of reactions of a chemical reaction.
• Type of determination in the rate of reaction;
1. Average rate of reaction (rate in a certain period of time)
2. Rate of reaction at a given time (instantaneous rate of reaction)
4) What is stated in the collision theory? • According to the collision theory, for a reaction to be occurred, the
particles of the reactants must:
ü collide with each other,
ü collide with the correct orientation,
ü achieve total energy that equals to activation energy.
5) What is activation energy? • The minimum energy in the system of reaction that the reacting
particles must possess to start a chemical reaction.
6) What is effective collision? • Collisions with the correct orientation and able to overcome the
activation energy of the system.
7) State the factors that affect the rate of a
chemical reaction.
• Factors that affect the rate of reaction;
1. Size of solid reactant
2. Concentration of solution reactant
3. Temperature of reactant
4. Presence of catalyst
5. Pressure of gas reactant
7) Explain how total surface area (size of
reactant) can increase the rate of
reaction based on collision theory.
(Specific : reaction between calcium carbonate and hydrochloric acid solution)
• When the size of solid calcium carbonate becomes smaller, the total
surface area exposed to collision increase.
• The frequency of collision between calcium carbonate and hydrogen
ions (the reacting particles) increase.
• This increases the frequency of effective collision between calcium
carbonate and hydrogen ions
• Hence the rate of reaction increases.
8) Explain how concentration can increase
the rate of reaction based on collision
theory.
(Specific : reaction between zinc powder and hydrochloric acid solution)
• When the concentration of hydrochloric acid solution increases,
the number of hydrogen ions per unit volume increases.
• Particles have more chances to collide more often.
• The frequency of collision between zinc atoms and hydrogen ions (the reacting particles) increase.
• This increases the frequency of effective collision between zinc atoms
and hydrogen ions
• Hence, the rate of reaction increases.
9) Explain how temperature can increase
the rate of reaction based on collision
theory.
(Specific : reaction between sodium thiosulphate solution and sulphuric acid solution)
• When the temperature of reactant increases, the kinetic energy of the
particles increases.
• Particles move faster and collide more often.
• The frequency of collision between thiosulphate ions and hydrogen
ions (the reacting particles) increase.
• This increases the frequency of effective collision between
thiosulphate ions and hydrogen ions.
• Hence, the rate of reaction increases.
17 10) Define the term catalyst • Catalyst is the substance which can alter the rate of a chemical
reaction while it remains chemically unchanged at the end of the
reaction.
11) Explain how catalyst can increase the
rate of reaction based on collision
theory.
(Specific : reaction in the decomposition of hydrogen peroxide by using manganese(IV) oxide powder)
• When a positive catalyst is used, it provides an alternative path with
lower activation energy.
• More collided hydrogen peroxide molecules are able to overcome that
lower activation energy.
• This increases the frequency of effective collision between hydrogen
peroxide molecules (the reacting particles).
• Hence, the rate of reaction increases.
Catalyst does not increase the frequency of collision between reacting particles.
12) If a graph of the reaction between
magnesium ribbon and sulphuric acid
solution 0.1 mol dm-3
is obtained as
follow (labelled as X), suggest how to
get graph Y with a higher gradient?
How to increase the rate of reaction?
Graph Y can be obtained by;
1. change with magnesium powder (smaller size of reactant)
2. use sulphuric acid 2.0 mol dm-3
(more concentrate solution)
3. heat the mixture of reactant (higher temperature)
4. add copper(II) sulphate solution (presence of catalyst)
13) State briefly, how the knowledge about
the factors that affect the rate of
reaction is applied in human daily life.
• Application of the rate of reaction;
1. Keep food in fridge
2. Cook food in smaller sizes
3. Use iron filling in Haber process
4. Use vanadium(V) oxide in Contact process
14) Food store in a refrigerator lasts longer
than food stored in a kitchen cabinet.
Explain why.
Temperature in refrigerator is lower. The lower temperature caused the
bacteria to be less active. A little toxin is released by the bacteria. The
rate of the food turns bad is lower.
Temperature in kitchen cabinet is higher. The higher temperature
caused the bacteria to be more reactive. A more toxic is released by the
bacteria. The rate of the food turns bad is higher
15) One kilogram of meat, cut into big
pieces, takes a longer time to cook
compared to one kilogram of meat cut
into small piece. Explain the above
statement based on the size of the
particles.
Meat cut into small pieces have smaller size compare to the meat cut
into big pieces.
The smaller the size, the bigger the total surface area of the meat, hence
the higher the rate of reaction.
16) What is hydrocarbon compound? • hydrocarbon is a compound that contains carbon atoms and hydrogen
atoms only in its molecule.
17) What is saturated and unsaturated
hydrocarbon?
State an example for each of them.
• Saturated hydrocarbon is the hydrocarbon compound that contains only
single covalent bond in its molecule
Example : ethane.
• Unsaturated hydrocarbon is the hydrocarbon compound that contains
multiple (double or triple) covalent bond (between carbon atoms) in
its molecule.
Example : ethene.
18) What is the meaning of structural
formula?
Formula that shows which atoms are bonded to each other in a molecule
of the organic compound.
Volume of H2 (cm3)
Time (s)
X Y
18 19) State the functional group and general
formula of each of the following
homologous series;
(a) Alkane
(b) Alkene
(c) Alcohol
(d) Carboxylic acid
(e) Ester
Homologous
series Functional group General formula
Alkane single covalent bond CnH2n+2
Alkene carbon-carbon double
covalent bond, -C=C-
CnH2n
Alcohol hydroxyl, -C-OH CnH2n+1OH
Carboxylic acid carboxyl, -COOH CnH2n+1COOH
Ester Carboxylate, -COOC- CnH2n+1COO CnH2n+1OH
20) What is isomerism? • Isomerism is the phenomenon whereby two or more molecules that
have the same molecular formula, but different structural formulae.
• All of isomers have same chemical properties (because have the same
functional group) but different physical properties.
21) Explain why on going down the alkane
series, the melting and boiling point
increase?
• The higher the number of carbon atoms per molecule, the higher the
melting point and boiling point
Explanation :
• When the number of carbon atoms increase, the alkane molecule
become bigger.
• The van der waals forces of attraction between molecules increase.
• Need more heat energy to overcome the forces of attraction
between molecules
22) Explain why alkanes are non-
conductors of electricity.
• Alkanes are covalent compounds made up of neutral molecules.
• They don’t have free moving ions.
• Hence alkanes are non-conductors of electricity.
23) Explain why ethene gas can
decolourises purple colour of the
acidified potassium manganete(VIl)
solution but ethane cannot
decolourises the acidified potassium
manganate(VII) solution.
• Ethene is an unsaturated hydrocarbon; it contains a carbon-carbon
double bond.
• Therefore, it can undergoes addition / oxidation reaction with the
acidified managanate(VII) solution.
• Ethane is a saturated hydrocarbon; it contains single bonds only.
• Therefore it cannot undergo any addition reaction.
24) Beside acidified potassium
manganate(VII) solution, state other
chemicals that can be used to
differentiate between the two
colourless liquid of hexane and
hexane. State also the observation.
1. Bromine water, Br2(aq)
Hexene turns brown bromine water to colourless.
2. Acidified potassium dichromate(IV) solution, K2Cr2O7(aq)/H+
Hexene turns orange colour of acidified potassium dichromate(IV)
solution into green.
25) Both hexane and hexene have six
carbon atoms per molecules, but
hexene burns with a more sooty flame.
Explain why
• This is because hexene contains a higher percentage by mass of
carbon atoms per molecule compare to haxane.
26) Pentane and propane are members of
alkane family. Explain why the melting
point of pentane is higher than
propane.
• The molecular size of pentane is bigger than that of propane.
• The intermolecular / van der Waals forces between molecules in
pentane are stronger.
• It needs more heat energy to overcome the stronger forces between
molecules.
27) State 5 characteristics of a
homologous series of carbon
compound.
1. Members can be represented by the same general formula.
2. The next member in series is differ by –CH2 with molar mass of 14
3. Physical properties of members change gradually as number of C
atoms increase.
4. Chemical properties of members are similar as they have same
functional group.
5. Members can be prepared by the same method.
28) State the name of process for the
following reaction:
a) Ethene to ethane
b) Ethene to ethanol
c) Ethanol to ethene
d) Ethanol to ethanoic acid
e) Ethanol + ethanoic acid to ethyl
ethanoate
• Name of process;
a) hydrogenation
b) hydration
c) dehydration
d) oxidation
e) esterification
19 29) Describe a test to differentiate between
hexane and hexene.
1) About 3 cm3 of hexane is poured into a test tube.
2) 3 drops of bromine in 1,1,1-trichloroethane are added into the hexane
in the test tube.
3) The mixture is shaken well.
4) The colour change of the solution in the test tube is recorded.
5) Steps 1 to 4 are repeated with hexene.
Result:
Hexene decolourises the brown bromine water.
Hexane does not decolourise the brown bromine water.
30) Write the chemical equations for each
of the following reaction;
a) Hydrogenation of ethene
b) Hydration of propene
c) Ethene + bromine
d) Ethene + acidified KMnO4(aq)
e) Polymerisation of ethene
f) Ethanol + conc. propanoic acid
g) EthanoI + acidified K2Cr2O7(aq)
h) Ethanoic acid + Mg ribbon
I) Propanoic acid + CaCO3
Chemical equation involved by carbon compounds
a) C2H4 + H2 ⎯→ C2H6
b) C3H6 + H2O(g) ⎯→ C3H7OH
c) C2H4 + Br2 ⎯→ C2H4Br2
d) C2H4 + H2O + [O] ⎯→ C2H4(OH)2
e) n C2H4 ⎯→ -[- C2H4 -]n-
f) C2H5OH ⎯→ C2H4 + H2O
g) C2H5OH + 2[O] ⎯→ CH3COOH + H2O
h) CH3COOH + Mg ⎯→ (CH3COO)2Mg + H2
h) 2 C2H5COOH + CaCO3 ⎯→ (C2H5COO)2Ca + H2O + CO2
31) Explain the coagulation process of
latex when formic acid is added.
• A rubber particle is made of long-chain rubber molecules enclosed by a
layer of protein membrane. The protein membrane is negatively
charged and causes the rubber molecules repel each other.
• When a dilute acid such us, methanoic acid (formic acid) is added
hydrogen ions, H+ from the acid neutralise the negative charges on the
protein membrane.
• As a result, the rubber particles become neutral and no longer repel
each other. The rubber particles collide each other and break the thin
protein membrane.
• The rubber molecules (polymers) are set free.
• The free moving rubber molecules come closer to combine with one
another and entangle.
• This enables the latex to coagulate.
32) Explain how to prevent coagulation of
latex.
• Alkali solution such as ammonia aqueous, NH3(aq) solution is usually
added to latex to preserve the latex in the liquid state.
• Ammonia solution, NH3(aq) contains hydroxide ions, OH- that neutralize
the acid produced by bacteria.
• This helps the rubber particles to remain their negative charges on the
protein membranes and preventing the latex from coagulating.
33) What is meant by oxidation and
reduction based on loss or gain of
oxygen?
• Oxidation is a gain of oxygen.
• Reduction is a loss of oxygen.
34) What is oxidation and reduction based
on transfer of electrons?
• Oxidation is the process of losing of electrons.
• Reduction is the process of gaining of electrons.
35) What is oxidation and reduction based
on changes in oxidation number?
• Oxidation occurs when there is an increasing in oxidation number.
• Reduction occurs when there is a decreasing in oxidation number.
36) What is redox reaction?
State an example of redox reactions.
• … is the chemical reaction involving oxidation and reduction that occur
simultaneously.
37) What is oxidising agent and reducing
agent based on the transferring of
electrons?
State an example of oxidising agent and
reducing agent
• Oxidising agent is chemical / reagent which receiving electrons and
itself undergoes reduction process.
Example : chlorine water, acidified KMnO4 solution
• Reducing agent is chemical / reagent which loses electrons and itself
undergoes oxidation process.
Example : zinc, potassium iodide solution
20 38) Determine whether the reaction
between hydrochloric acid and sodium
hydroxide is a redox reaction.
Explain your answer based on changes
in oxidation number.
• No. Neutralisation is not a redox reaction.
• There is no change of oxidation number of any atom or particle in the
reaction.
39) The reaction between zinc and
copper(II) sulphate solution is a redox
reaction. Explain why.
• Zinc undergoes oxidation because its atom donates 2 electrons to form
zinc ion, Zn2+
.
• Copper(Il) ion, Cu2+
undergoes reduction because it receives 2
electrons from zinc atom to form copper atom.
• The oxidation and reduction process occur simultaneously.
40) Chlorine water is added to potassium
iodide solution in a test tube. 2cm3 of
1,1,1-trichloroethene is added into the
test tube and the mixture is shaken
thoroughly. The colour of 1,1,1-
trichloroethene changes from colourless
to purple. Explain the observation.
• Chlorine water is an oxidising agent.
Cl2 + 2e à 2Cl-
• Chlorine oxidises iodide ion to iodine.
2I-
à I2 + 2e
• The presence of iodine gives purple colour in 1,1,1-trichloroethene
layer.
41) Describe the rusting process of an iron
bar.
• Iron surface under the centre of a water droplet acts as the anode
(negative terminal).
• Iron surface at the edge of the water droplet serves as the cathode
(positive terminal).
• At the anode, iron atoms lose electrons to form iron(II) ions.
Fe(s) ⎯→ Fe2+
(aq) + 2e (Oxidation)
Iron(Il) ions dissolve in water.
• Electrons flow to the edge of the water droplet (cathode) and are
received by oxygen and water molecules to form hydroxide ions.
O2(g) + 2 H2O(l) + 4 e ⎯→ 4 OH-
(aq) (Reduction)
• The Fe2+
ions combine with OH- ions to form iron(II) hydroxide.
Fe2+
(aq) + 2 OH-
(aq) ⎯→ Fe(OH)2(s)
• The iron(II) hydroxide is then further oxidised by oxygen to form
hydrated iron(III) oxide, Fe2O3.xH2O (brown substance known as rust),
whereby x varies.
Fe(OH)2(s) /012341/5
Fe2O3.xH2O
42) When iron is in contact with
magnesium, rusting of iron is prevented.
Explain why?
• Magnesium is more electropositive than iron.
• Magnesium is dissolved / corroded to form magnesium ions.
Mg(s) ⎯→ Mg2+
(aq) + 2e
• Iron(II) ions, Fe2+
are not present. Thus, iron is prevented from rusting.
43) When iron is in contact with copper,
rusting of the iron is speed up. Explain
why?
• Iron is more electropositive than copper.
• Iron is corroded to form iron(II) ion, Fe2+
.
Fe(s) ⎯→ Fe2+
(aq) + 2e
• The presence of copper increase the rate of the formation of iron(II)
ions, Fe2+
. As a result, the rusting of iron is speed up.
44) What is exothermic reaction and
endothermic reaction?
State an example for each reaction.
• Exothermic is a chemical reaction that gives out heat to the
surroundings
Example : 2 Na(s) + 2 H2O(I) ⎯→ 2 NaOH(aq) + H2(g)
• Endothermic is a chemical reaction that absorbs heat from the
surroundings.
Example : NaHCO3(s) + HCI(aq) ⎯→ NaCI(aq) + H2O(l) + CO2(g)
45) What is heat of precipitation? • The heat release when one mole of a precipitate is formed from their
ions in aqueous solution.
46) What is heat of displacement? • The heat release when one mole of a metal is displaced from its salt
solution by a more electropositive metal.
47) What is heat of neutralisation? • The heat release when one mole of water is formed from the reaction
between an acid and an alkali.
21 48) What is heat of combustion?
• The heat release when one mole of a substance (fuel) is completely
burnt in oxygen under standard conditions.
49) Explain why the heat of combustion of
butanol is higher than ethanol.
• The number of carbon atoms and hydrogen atoms per molecule of
butanol is higher than ethanol.
• When more carbon atoms and hydrogen atoms are burnt, more carbon
dioxide and water molecules are formed.
• This will cause more chemical bonds to be formed and more heat
energy to be released.
50) Explain why the heat of neutralisation
between strong acid and strong alkali is
a constant, which is -57 kJmol-1
.
• All neutralisation between a strong acid and a strong alkali are the
same.
• It only involves the reaction between hydrogen ions, H+ from the acid
and hydroxide ions, OH- from the alkali to produce molecules of water,
H2O.
H+ + OH
- ⎯→ H2O
51) Explain why the heat of neutralisation
between ethanoic acid and sodium
hydroxide is less than -57 kJ mol-1
.
• This is because ethanoic acid is a weak acid which exists as molecules
when they dissolve in water.
• They only ionise partially in water to produce low concentration of
hydrogen ions, H+
• Some of the heat given out during neutralisation reaction is used in
used to ionise the acid molecules completely to produce hydrogen
ions.
• As a result, the value of ΔH is always less than -57 kJ mol-1
.
52) What is soap? • Soap is the sodium or potassium salts of fatty acids.
53) What is saponification process? • It is an alkaline hydrolysis reaction to produce soap.
54) What is detergent? • Detergent is sodium salt of sulphonic acid.
55) What is hard water? • … is the water that contains magnesium ions, Mg2+
or / and calcium,
Ca2+
ions.
56) State the function of each of the
following additives in detergent
a) Whitening agent (example: sodium
perborate)
b) Optical brightener (fluorescent dies)
a) Biological enzyme (example:
amylase, lipase, protease and
cellulase)
d) Fragrance
• Function of additives in detergent.
a) Bleach the white fabric but does not bleach the dye on the coloured
fabrics.
b) Convert some ultraviolet radiation to blue light and cause the fabrics
looked brighter and whiter rather than yellow.
c) Break down and remove stains such as proteins, fats, carbohydrates,
blood and oil.
d) Give detergent and fabrics a better smell.
57) State the function of each of the
following food additives.
a) Preservatives (E.g.: Sodium nitrite,
sodium benzoate)
b) Antioxidants (E.g.: Ascorbic acid)
a) Flavourings (E.g.: Monosodium
glutamate, Aspartame)
d) Stabilisers
e) Thickeners
• Function of food additives;
a) To slow down or prevent the growth of bacteria or fungi, so that the
food can be kept longer.
b) To prevent oxidation that causes rancid fats and brown fruits.
c) To improve the taste or smell of food and restore taste loss due to
food processing.
d) To helps to mix two liquids that usually do not mix together to form an
emulsion.
e) Substance that thicken the food and give the food firm, smooth and
uniform texture.
58) State the functions of the following
modem medicines;
a) Analgesics (e.g.: paracetamol,
aspirin, codeine)
b) Antibiotics (e.g.: penicillin,
streptomycin)
a) Psychotherapeutic medicine (e.g.:
stimulant, antidepressant,
antipsychotic)
• Function of modern medicine;
a) to relieve pain.
b) to treat infections caused by bacteria
c) to alter abnormal thinking, feeling or behaviour.
Stimulant : To increase or maintain alertness of the central nervous system.
Antidepressant : To treat depression Antipsychotic : To treat psychiatric illness.
59) Explain why the cleansing action of a
detergent is more effective than soap in
hard water.
• Soap reacts with magnesium or calcium ions to form an insoluble
precipitate called as scum.
• Foams cannot be formed and soap fail to clean.
• Detergent reacts with magnesium or calcium ions to form soluble
substance. It does not form scum.
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