Fakta Kimia Spm 2015

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


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)


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.


presence of chloride ions, CI- in a

solution.


• 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.


presence of sulphate ions, SO4

2- in a

solution.


• 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.


presence of nitrate ions, NO3

-, in a

solution.


• 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


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.


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.


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).


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.

Fakta Kimia Spm 2015

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