Chapter 3
Oceans
Chapter Exercise
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
sodium chloride (common salt), sodium, chlorine
evaporation
filtration, crystallization
saturated
boiling, condensation
distillate, residue
distillation
flame test
brilliant golden yellow
white
water, white, blue, blue, pink
Brine
hydrogen, chlorine, sodium hydroxide
B
C
B
C
D
A
20. (a) Filtration
(b)
glass rod
sand + sodium chloride solution
folded filter paper
sand
filter funnel
sodium chloride solution
stand
(c) Distillation
(d)
thermometer
clamp
boiling tube
delivery tube
receiver test tube
sodium chloride
heat
solution
anti-bumping granule
water
pure water
(e) Test for sodium ions: Flame test.
The sample gives a brilliant golden yellow flame in the flame test if sodium
ions are present.
Test for chloride ions: Silver nitrate test
Add silver nitrate solution to the sample, followed by excess dilute nitric
acid. The appearance of a white precipitate indicates the presence of
chloride ions.
21. His conclusion is not justified. He should add the white-powder to distilled water
and stir well, then filter and evaporate the filtrate to dryness by heating, and see
if any solid is left.
22. (a) This is because some metal ions can produce a characteristic coloured light
when they are heated strongly.
(b) (1) Moisten a clean platinum wire with concentrated hydrochloric acid.
(2) Dip the platinum wire into a crushed sample of the salt (or solution) to
be tested.
(3) Heat the platinum wire with the sample strongly in a non-luminous
flame.
(4) Observe the colour of the flame at the wire and identify the metal ions
present.
(c) Potassium ions: lilac; calcium ions: brick red; copper (II) ions: bluish green.
23. (a) It was not a suitable method because the liquid may be unclean, harmful or
even poisonous.
(b) Flame test.
(c) To show the presence of chloride ions, acidified silver nitrate solution is
added to the sample. If chloride ions are present, a white precipitate will be
formed.
(d) To show the presence of water, a few drops of the liquid are added to
anhydrous copper(II) sulphate.
The powder changes from white to blue if water is present.
Alternatively, add a few drops of the liquid to dry cobalt chloride test paper.
The paper changes from blue to pink if water is present.
(e) He could not be sure that the liquid was sea water. Even if the tests showed
that sodium ions, chloride ions and water were present, the liquid might not
necessarily be sea water. For example, it might be just a sodium chloride
solution, without any other salts naturally present in sea water.
24. (a) Electrolysis means ‘decomposition by electricity’.
(b) Chlorine, hydrogen and sodium hydroxide.
(c) Chlorine  water sterilization, manufacture of bleach, etc.
Hydrogen  production of margarine, as rocket fuel, etc.
Sodium hydroxide  manufacture of soap, extraction of aluminium, etc.
25.
 Sea water is an important source of common salt (sodium chloride) which has
many uses.
 By the electrolysis of sea water, useful products, hydrogen, chlorine and
sodium hydroxide are obtained. These products can be used to manufacture a
lot of useful chemicals.
 Hydrogen can be used to produce ammonia.
 Chlorine can be used to produce bleach.
 Sodium hydroxide can be used to produce soap.
Chapter 4
Rocks and minerals
Class Practice
A4.1
Step 1:
Step 2:
Step 3:
Step 4:

 calcium oxide + carbon dioxide
calcium carbonate heat
calcium oxide + water  calcium hydroxide
calcium hydroxide + water  calcium hydroxide solution (limewater)
calcium hydroxide solution (limewater) + carbon dioxide
 calcium carbonate + water
A4.2
calcium carbonate + nitric acid  calcium nitrate + carbon dioxide + water
Chapter 4
Rocks and minerals
Chapter Exercise
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
27.
28.
29.
30.
31.
mineral, a mixture of minerals
crystalline, chemical
extraction
ore, aluminium
haematite, carbon (or coke)
chalk, marble
Neutralizing, building material, cement (or other acceptable answers)
Weathering
Erosion
Physical
Chemical
uicklime, calcium oxide.
acids, carbon dioxide
milky
iron + carbon dioxide
aluminium + oxygen
carbonic acid
calcium hydroxide + heat
calcium hydrogencarbonate
calcium oxide + carbon dioxide
calcium carbonate (white solid) + water
calcium chloride + carbon dioxide + water
B
D
D
C
A
B
D
C
C
B
32. (a) (1)
(2)
(b) (1)
(2)
Both react with acid to give out carbon dioxide.
Both are decomposed on strong heating.
Neutralizing acidic soil and lakes affected by acid rain.
As a raw material to make glass by heating with sand and sodium
carbonate.
(3) As a raw material to make cement by heating with clay. (or any other
possible answers)
33. (a) Weathering is the slow process in which exposed rocks are broken down
into smaller pieces.
(b) Physical weathering and chemical weathering.
(c) It is because carbon dioxide in air dissolves slightly in rainwater, forming
carbonic acid. Carbonic acid can attack rocks.
(d) Calcium hydrogencarbonate
(e) calcium carbonate + carbonic acid  calcium hydrogencarbonate
34. (a) Calcium carbonate
heat
(b) calcium carbonate strong

 calcium oxide + carbon dioxide
(c)
delivery tube
limewater
limestone
heat
(d) When the gas is passed through limewater for a few seconds, the limewater
turns milky.
35. (a) (i)
(ii)
(iii)
(b) (i)
(ii)
Calcium oxide
Calcium hydroxide
Calcium hydroxide solution
heat
calcium carbonate 
 calcium oxide + carbon dioxide
calcium carbonate + hydrochloric acid  calcium chloride + carbon
dioxide + water
(iii) calcium oxide + water  calcium hydroxide
(iv) carbon dioxide + calcium hydroxide solution
 calcium carbonate + water
(c) The rock fizzes (colourless gas is given out).
Chapter 9
Structures and properties of substances
Class Practice
A9.1
(a) Simple molecular structure, giant covalent structure
(b) Simple molecular structure, macromolecules, giant covalent structure
A9.2
Iodine, bromine, chlorine and fluorine have a simple molecular structure and their
molecules are held by weak intermolecular forces called van der Waals' forces. The
larger the molecular size, the greater the van der Waals' forces. The molecular sizes of
the substances are: I2 > Br2 > Cl2 > F2. Therefore, the strength of the van der Waals'
forces are: I2 > Br2 > Cl2 > F2.
A9.3
(a) Low-melting.
(b) No. They are soft.
(c) No
(d) (i) No
(ii) Yes
A9.4
(a) (i) No
(ii) No
(b) No
A9.5
(a) 2
(b) 2
A9.6
(a) C. It conducts electricity when solid.
(b) B. It does not conduct electricity when solid, but conducts when molten.
(c) A. It does not conduct electricity whether solid or molten, and has a low melting
point.
(d) D. It does not conduct electricity whether solid or molten; and has a very high
melting point.
(e) A. Substances with a simple molecular structure are usually soluble in
non-aqueous solvents (such as heptane).
A9.7
(a) The compound formed between a Group II element X (a metal) and a Group VII
element Y (a non-metal) is an ionic compound.
Element X forms X2+ ions;
Element Y forms Y ions.
The formula of the compound is thus XY2.
(b) It has a giant ionic structure.
(c) Its physical properties are similar to those mentioned in the answer to Example
9.3, part (a) (iii).
Chapter 9
Structures and properties of substances
Chapter Exercise
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
giant
molecules, covalent bonds, intermolecular forces (or van der Waals’ forces)
giant, giant lattice (or network)
low, non-conductors, insoluble, soluble, non-aqueous solvents
solid, high, molten, aqueous solution, soluble, insoluble, non-aqueous
solids, high, graphite, non-conductors, insoluble
structure
giant metallic, metallic, metal ions, sea, delocalized electrons
delocalized electrons, non-directional.
C
A
A
B
A
C
B
17. (a) Covalent bonding
(b) Giant covalent structure
(c) Diamond
carbon atom
Quartz
oxygen atom
silicon atom
(d)
(e)
(f)
(g)
Diamond > quartz> glass
Quartz is a crystalline solid while glass is a non-crystalline solid.
Diamond
Diamond
18. (a) X: Giant ionic structure;
Y: Giant covalent structure;
Z: Simple molecular structure
(b) X: Sodium chloride;
Y: Diamond;
Z: Iodine (Accept other reasonable answers)
(c) X: ionic bond;
Y: covalent bond;
Z: van der Waals’ forces
(d) (i) X has a higher melting point than Z as X has a giant ionic structure
while Z has a simple molecular structure.
(ii) Y has a higher melting point than Z as Y has a giant covalent structure
while Z has a simple molecular structure.
19. (a) Substance B
(b) (i) Substance E is a metal because it conducts electricity in solid state.
(ii) Substance A is an ionic compound because it does not conduct
electricity in the solid state but conducts electricity when molten.
(iii) Substances B and C are covalent compounds with simple molecular
structure because both of them do not conduct electricity whether in
the solid state or in molten form. Besides, they have low melting
points.
(iv) Substance D is a covalent compound with giant covalent structure
because it does not conduct electricity whether in the solid state or in
molten form and has a very high melting point.
(c) Substances B and C are likely to be soluble in heptane (a non-aqueous
solvent.)
20. – The melting point of the above compounds follows the order: CO2 < Li2O <
SiO2
– SiO2 has a giant covalent structure. It has the highest melting point. To melt
the compound, large amount of energy is required to break the strong covalent
bonds among the atoms in SiO2.
– CO2 has a simple molecular structure. It has the lowest melting point. To melt
the compound, relatively small amount of energy is required to break the weak
intermolecular forces among the molecules of CO2.
– Li2O has a giant ionic structure. It has a melting point in between SiO2 and
CO2. To melt the compound, energy is required to break the strong ionic bonds
among the ions in Li2O.