Sunday, June 29, 2014

Chapter 10 WB Solutions

Interactive Science (Second Edition) Workbook Solutions
1
INTERACTIVE SCIENCE (Second Edition) 2B
Workbook Solutions
Chapter 10 COMMON ACIDS AND ALKALIS
Sectional Exercise
Sections 10.1 & 10.2
A. Concept checking p.25
1. True
2. False
3. False
4. True
5. False
6. True
B. Multiple choice p.25
1. B
2. D
3. B
4. C
5. B
6. A
7. A
C. Fill in the blanks p.27
1. sour
2. opposite
3. (a) bitter
(b) soapy / slippery
4. (a) sodium hydroxide
(b) potassium hydroxide
(c) protective gloves / gloves
5. (a) slow running water / the tap
(b) 10
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Section 10.3
A. Multiple choice p.27
1. B
2. D
3. C
4. A
5. A
B. Fill in the blanks p.28
1. (a) blue
(b) red
(c) red
(d) blue
(e) Neutral
2. (a) degree
(b) acidic
(c) neutral
(d) alkaline
C. Questions p.29
1. (a) ii
(b) iv, vii
(c) v, vi
(d) iii
(e) i, viii
2. (a) Its pH value may be 2.5 – 5.
(b) Carbon dioxide is boiled off. There is no / less carbonic acid. The amount of acid
in the drink decreases, so the drink becomes less acidic and its pH value increases.
3. (a) Use a piece of pH paper / a pH meter / universal indicator solution to measure its
pH value.
(b) Silk Liquid Soap
(c) ABC Liquid Soap
(d) Silk Liquid Soap has a pH value of 5.5, which is the same as the pH value of
healthy skin. It is better for our skin. Soap solution has a pH value of 10, which is
significantly higher than the pH value of our skin and may irritate / harm our skin.
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Section 10.4
A. Concept checking p.31
1. False
2. True
3. True
4. True
B. Multiple choice p.31
1. D
2. A
3. C
4. C
5. B
C. Matching p.32
(a) ii
(b) i
(c) iv
(d) iii
D. Question p.33
(a) The gas is not hydrogen.
(b) (i)
(or other reasonable answers)
(ii) The gas is carbon dioxide.
(c) Calcium carbonate
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Section 10.5
A. Concept checking p.34
1. False
2. True
3. True
4. True
B. Multiple choice p.34
1. B
2. D
3. D
4. C
C. Questions p.35
1. (a) Rainwater that has a pH value lower than 5.6.
(b) Sulphur dioxide and nitrogen oxides
(c) Calcium carbonate
(d) Calcium carbonate in limestone reacts with acid rain. Calcium carbonate dissolves
and gives off carbon dioxide in the process.
(e) • Making the water in lakes and rivers so acidic that fish and plants cannot
survive.
• Making soil too acidic and thus affecting plant growth.
(or other reasonable answers)
2. A small amount of vinegar was left in the bottle. The water she used to water her plants
was therefore acidic. As a result, the soil became too acidic for plant growth and the
plants died.
Section 10.6
A. Concept checking p.36
1. False
2. True
3. True
4. True
B. Multiple choice p.36
1. D
2. C
3. C
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C. Questions p.37
1. (a) Concentrated sulphuric acid
(b) Corrosive
(c) Wash the affected area under slow running water immediately for at least 10
minutes, and remove the affected clothes.
2. (a) • Wear protective gloves.
• Wear safety goggles.
• Wear a laboratory coat.
• Perform the dilution in a fume cupboard.
(b) Instead of pouring water into the beaker of concentrated nitric acid, Peter should
add the acid slowly to a large amount of water and stir the solution carefully with a
glass rod.
Section 10.7
A. Multiple choice p.38
1. B
2. B
3. D
B. Fill in the blanks p.39
1. (a) alkali
(b) salt
2. (a) potassium nitrate
(b) (i) hydroxide
(ii) hydrochloric acid
(iii) calcium
C. Question p.39
(a) To show the pH value of the solution in the beaker.
(b) 13
(c) (i) 7
(ii) 9.0 cm3
(iii) Sodium hydroxide + hydrochloric acid sodium chloride + water
(iv) Evaporation
(d) (i) 1.8
(ii) Its pH value is lower than 1.8. For 15 cm3 of the acid added, 9 cm3 is used to form
a neutral solution with sodium hydroxide and 6 cm3 of the acid is in excess. The excess
acid diluted by the neutral solution formed and the resulting solution is less acidic than
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the acid used in this experiment. Thus, the acid used should have a lower pH value
than the resulting solution.
Section 10.8
A. Concept checking p.40
1. True
2. True
3. True
4. False
B. Multiple choice p.41
1. D
2. C
3. D
4. C
5. A
6. B
C. Matching p.42
(a) i
(b) iii
(c) ii
D. Questions p.42
1. (a) The medicine is an alkali because it is used to neutralize the excess acid in Leo’s
stomach. The medicine is a weak alkali instead of a strong alkali, because strong
alkalis are corrosive and may hurt his stomach.
(b) Magnesium hydroxide and aluminium hydroxide
2. (a) It is a strong acid and it can corrode the metal kettle.
(b) (i) Vinegar / ethanoic acid / lemon juice / citric acid
(or other reasonable answers)
(ii) • It contains / is a weak acid that will not damage the metal kettle if used
for a short period of time.
• Calcium carbonate dissolves in the acid and reacts with it to form
harmless products.
• It is not harmful to humans.
(any two or other reasonable answers)
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3. (a) Electroplating, dyeing (or other reasonable answers)
(b) Acids in the acidic waste can be neutralized by adding alkalis like sodium
hydroxide. Alkalis in the alkaline waste can be neutralized by adding acids like
sulphuric acid.
4. (a)
(b) pH meter
(c) 4 tablets
(d) • Break / crush the antacid tablet into powder.
• Stir the solution with a glass rod after adding the antacid powder.
(e) Measure the mass of three antacid tablets using an electronic balance. Add them
into a beaker containing 100 cm3 of dilute hydrochloric acid. Stir the solution with a
glass rod until all the tablets dissolve. Crush one antacid tablet into powder using a
mortar and a pestle. Measure the mass of the antacid powder. Continuously measure
the pH value of the solution using a pH meter and add antacid powder in small
amounts to the solution until its pH value suddenly rises above 7. Measure the mass of
remaining antacid powder and calculate the total mass of antacid added (i.e. the mass
of antacid required to neutralize 100 cm3 of dilute hydrochloric acid.)
Integrated Exercise
A. Concept checking p.45
1. True
2. False
3. True
4. True
5. True
6. True
7. False
8. False
9. True
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10. False
B. Multiple choice p.45
1. C
2. B
3. B
4. C
5. A
6. A
7. A
8. D
9. A
10. C
11. A
12. C
C. Questions p.48
1. (a) Solution A: vinegar
Solution B: rainwater
Solution C: soap solution
Solution D: lime water
(b) Its pH value may be between 8.8 and 12.3.
2. (a) Indicators P and T
(b) Indicators Q and R are blue in ammonia.
(c) Indicator Q is yellow in both acids. Indicator S is colourless in both acids.
(d) Indicator P is yellow in ethanoic acid and in sodium hydroxide.
(e) Indicator P is red in a solution with a pH value equal to or less than 2. Indicator T
is yellow in a solution with a pH value in between 2 and 8. If a solution looks red after
adding indicator P and yellow after adding indicator T, it means that the solution has a
pH value of about 2.
3. (a) Red
(b) Concentrated hydrochloric acid gives off an acidic vapour. The acidic vapour
dissolves in the water in the moist blue litmus paper and turns the litmus paper red.
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4. (a) Colourless gas bubbles are given out.
(b) (i) The lime water turns milky.
(ii) The gas released in the reaction is carbon dioxide.
(c) Marble / calcium carbonate / other carbonates
5. (a)
(b) (Take out the test tube containing the gas from the set-up in (a).) Put a burning
splint near the mouth of the test tube. If the gas burns with a ‘pop’ sound, it is
hydrogen.
(c) (i) Hydrogen gas will be given out at a slower rate.
(ii) There will be no reaction. / No hydrogen gas will be collected.
6. (a) The air in Sai Kung is the least polluted. The pH value of the rainwater sample
collected there was 5.5, which is closest to the pH value of 5.6 of clean / normal rain.
(b) (i) The air in Tsuen Wan and Causeway Bay is the most polluted. The pH
values of the rainwater samples collected in these areas were the lowest among
the areas shown. This means that the rainwater was highly polluted by acidic
pollutants / sulphur dioxide and nitrogen oxides and was the most acidic.
(ii) Tsuen Wan: factories and motor vehicles (Tsuen Wan is an industrial area
with heavy traffic.) Causeway Bay: motor vehicles (Causeway Bay has heavy
traffic.)
(c) (i) The rainwater becomes more acidic during winter.
(ii) The southern part of Guangdong is heavily polluted with acidic pollutant
gases / sulphur dioxide and nitrogen oxides released from the factories and power
stations there. When these gases are blown from the north-east to Hong Kong in
winter, the rainwater collected in Sheung Shui and Sai Kung (located in
north-eastern parts of Hong Kong) becomes more acidic and the pH value of
rainwater decreases.
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7. (a) E
(b) (i) C
(ii) Dilute sodium hydroxide is alkaline and its initial pH value is higher than 7.
As water is added, the sodium hydroxide becomes more dilute and less alkaline.
The pH value of the solution decreases. However, when more water is added, the
pH value of the solution further decreases but is still higher than 7, because the
solution is still sodium hydroxide (although more dilute), which is alkaline.
8. (a) Sodium hydroxide + hydrochloric acid sodium chloride + water
(b) No. Sodium hydroxide is corrosive. Although it can neutralize hydrochloric acid,
some of it will contact and stay on Charles’ hand and hurt his hand. Charles should
wash his hand under slow running water for at least 10 minutes instead.
9. (a) Soap solution (or other weak alkalis)
(b) (i) No. Caustic soda (sodium hydroxide) is a strong alkali. It is corrosive.
(ii) Oven cleaner (or other reasonable answers)
(c) Vinegar and lemon juice (or other weak acids)
Quick Review
A. The pH scale p.54
(a) hydrochloric acid
(b) orange juice
(c) distilled water
(d) glass cleaner
(e) sodium hydroxide
(f) acidity
(g) neutral
(h) alkalinity
B. Reactions of acids with various substances p.54
(a) (i) iron
(ii) zinc
(iii) magnesium
(iv) Hydrogen
(v) warm
(vi) heat
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(b) (i) marble
(ii) limestone
(iii) Carbon dioxide
(c) (i) salt
(ii) water
(iii) sodium chloride + water
(iv) nitric acid + potassium hydroxide potassium nitrate + water
(v) sulphuric acid + calcium hydroxide calcium sulphate + water
C. Causes and effects of acid rain p.56
(a) sulphur dioxide
(b) nitrogen oxides
(c) acids
(d) rivers
(e) lakes
(f) acidic
(g) corrode
D. Safety measures for handling concentrated strong acids and alkalis p.56
(a) fume cupboard
(b) toxic
(c) irritant
(d) safety goggles
(e) eyes
(f) protective gloves
(g) laboratory coats
(h) burns
STSE Article Reading p.57
(a) • Wax does not react with acids. / Wax is not corroded by acids.
• Wax can be scratched off easily as it is soft.
• Wax can be removed easily without damaging the printing plate.
(any two or other reasonable answers)
(b) When the metal plate is dipped into acid, the exposed metal along the lines of the
design is corroded by the acid, leaving grooves of the design on the metal.
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(c) Metal: zinc / iron / magnesium
Acid: sulphuric acid / hydrochloric acid / nitric acid / ethanoic acid
(or other reasonable answers)
(d) Wear protective gloves. (or other reasonable answers)
Little Einstein’s Corner p.58
1. (a) (i) Corrosive
(ii) The police would prevent people from getting near the site.
(or other reasonable answers)
(b) The chemist could collect a water sample from the river and measure its pH value
using pH paper, universal indicator solution or a pH meter. If the pH value was lower
than normal, acid had leaked into the river.
(c) Add limestone (calcium carbonate) or slaked lime (calcium hydroxide) to the
river to neutralize the acid.
(d) The iron drain cover reacted with the acid and produced hydrogen gas.
2.
Test Observation and conclusion
1. Use droppers to add a drop of each of
the chemicals to a piece of red litmus
paper.
The chemical that turns the red litmus
paper blue is sodium hydroxide
solution.
2. Pour each of the remaining three
chemicals into a test tube. Use a spatula
to add calcium carbonate powder to
each test tube.
The chemical that gives out colourless
gas bubbles is hydrochloric acid.
3. Use droppers to add a few drops of the
remaining two chemicals onto a watch
glass separately. Heat each of them
until the chemical is totally evaporated
over beaker of water bath.
Distilled water does not give any
residue, while sodium chloride solution
gives a white powder (i.e. table salt).
3. (a) It is affected by acid rain. (or other reasonable answers)
(b) The soil is too acidic for healthy plant growth.
(c) (i) Use pH paper / universal indicator solution.
(ii) It is worse, because the pH values obtained from a pH paper / universal
indicator solution is less accurate than those obtained from a pH meter.
(d) Weak alkali
(e) Amount of limestone required = 35 kg × (80 m2 / 100 m2) = 28 kg

Chapter 8 WB Solutions

Interactive Science (Second Edition) Workbook Solutions
1
INTERACTIVE SCIENCE (Second Edition) 2A
Workbook Solutions
Chapter 8 MAKING USE OF ELECTRICITY
Sectional Exercise
Section 8.1
A. Concept checking p.51
1. False
2. True
3. False
4. True
5. True
B. Multiple choice p.51
1. (a) electrical conductors
(b) electrical insulators
2. (a) closed
(b) open
C. Question p.52
1. (a) electrical insulator
(b) electrical conductor
(c) electrical insulator
(d) electrical conductor
(e) electrical insulator
(f) electrical insulator
(g) electrical insulator
(h) electrical conductor
(i) electrical conductor
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2.
3. (a) (i) will not
(ii) do not form
(b) (i) will
(ii) form a closed circuit
(c) (i) will
(ii) the bulb, the dry cells and the wires form a closed circuit
(d) (i) will not
(ii) electrical energy in the circuit
4. No. The wheels of the tram are connected with the power supply through the rails, and
the circuit is complete. (or other reasonable answers)
Sections 8.2 & 8.3
A. Multiple choice p.54
1. (a) ampere
(b) volt
2. free electrons
3. 1.5
4. (a) ammeter
(b) voltmeter
5. larger
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B. Question p.55
1. (a) dry cell
(b) wire
(c) free electrons
2. (a)
(or other reasonable answers)
(b) Connect one more dry cell to the circuit, such that the positive poles of the
dry cells point to the same direction. (or other reasonable answers)
(c)
(or other reasonable answers)
(d) The ammeter in (c) has a higher reading because the total voltage of two dry cells
is higher than that of one dry cell, and hence the current is larger. (or other
reasonable answers)
3. (a)
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(b)
(c) The reading of the voltmeter is 3.0 V.
Section 8.4
A. Multiple choice p.57
1. ohm
2. smaller
3. higher
4. higher
5. rheostat
B. Multiple choice p.57
1. A
2. C
3. D
4. C
C. Question p.59
1. (a)
(Electric current of the opposite direction is also correct.)
(b) In anti-clockwise direction
(c) (i) Connect terminals B and C to the circuit.
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(ii) In clockwise direction
(d) Dimmers on a lighting system / Volume controls on hi-fi systems (or other
reasonable answers)
2. Measure the resistance of the bulb. If the measured resistance is infinitely high, the
filament is broken.
Section 8.5
A. Multiple choice p.60
1. D
2. C
3. B
4. C
B. Question p.61
1. (a) dry cell
(b) battery
(c) bulb
(d) ammeter
(e) voltmeter
(f) resistor
(g) rheostat
(h) switch
2. (a)
(b)
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(c)
(d)
(e)
Section 8.6
A. Concept checking p.63
1. True
2. True
2. False
3. False
4. False
5. True
B. Multiple choice p.63
1. D
2. B
3. B
4. B
5. A
6. B
7. C
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C. Multiple choice p.66
1. (a) parallel
(b) can
2. (a) series
(b) cannot
D. Question p.66
1.
In series In parallel
a, c, f b, d, e
2. (a)
(or other reasonable answers)
(b) Voltmeter and resistor
(c) Move the sliding contact towards Q .
(Answer depends on how the wires are connected in (a).)
(d) Connect one more dry cell to the circuit. / Replace the resistor with another one of
lower resistance. (or other reasonable answers)
Section 8.7
A. Concept checking p.68
1. True
2. True
3. False
4. False
5. True
6. False
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B. Multiple choice p.68
1. B
2. C
3. B
C. Question p.69
1. (a) (i) fuse rating
(ii) thin wire
(iii) glass wiring
(iv) metal contact cap
(b) A fuse protects an electrical appliance from being damaged by an excessive
electric current.
(c) In series
2. (a)
(b) (i) fuse rating
(ii) current
(iii) melt
(c) Yes, because a fuse of a higher melting point can allow a larger current to pass
through it.
Section 8.8
A. Multiple choice p.70
1. B
2. C
3. B
4. D
5. A
6. A
7. A
B. Fill in the Blanks p.73
1. 220 V
2. (a) earth
(b) neutral / live
(c) live / neutral
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3. (a) earth
(b) earth / ground
(c) leakage
4. overloaded
C. Question p.73
1. (a) live
(b) brown
(c) neutral
(d) blue
(e) earth
(f) yellow and green
(g) fuse
2. (a) A short circuit happens.
(b) After the switch is closed, a path with a very low resistance is formed. The electric
current flowing through the fuse becomes very large. The fuses melts and breaks
the circuit.
Section 8.9
A. Concept checking p.74
1. True
2. False
3. True
4. False
5. True
6. False
7. False
8. True
9. True
B. Question p.74
1. (a) (i) power
(ii) voltage
(b) Electric current flowing through bulb A = 40 W / 220 V = 0.18 A
Electric current flowing through bulb B = 60 W / 220 V = 0.27 A
2. Power of the rice cooker = 5 A × 220 V = 1100 W
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3. (a) Electric current = 500 W / 220 V = 2.27 A
(b) Electric current = 1000 W / 220 V = 4.55 A
(c) Resistor B has a lower resistance because it allows a larger current to flow through
it.
4. (a) Electric current = 800 W / 220 V = 3.64 A
(b) 0.8 × 6 = 4.8 kW h
(c) 4.8 kW h × 0.9 × 30 = $129.6
5. (a) 800 × 0.06 × 16 = 768 kW h
(b) 800 × 0.005 × 16 = 64 kW h
(c) (768 – 64) × $0.9 = $633.6
(d) For a filament bulb, more energy is lost as heat to the surroundings. (or other
reasonable answers)
6. (a) 10923 – 10121 = 802
(b) Cost per unit = $705.76 / 802 = $0.88
(c) Amount saved = 3 × 1.2 kW × 120 h × $ 0.88 = $380.16
Section 8.10
A. Concept checking p.77
1. False
2. False
3. False
4. False
5. True
B. Question p.78
1.
Electrical appliances working on the
magnetic effect of an electric current
Electrical appliances working on the
heating effect of an electric current
a, b, c, d, f, g a, e, h, i
2. (a) When an electric current flows through the coil, a magnetic effect is produced. The
metal coil behaves like a magnet to attract the iron parts of the waste.
(b) No, because plastic cannot be attracted by the current-carrying metal coil /
electromagnet.
(c) The crane can be used to attract iron and steel objects and separate them from
household rubbish. (or other reasonable answers)
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Integrated Exercise
A. Concept checking p.79
1. False
2. True
3. False
4. False
5. True
6. True
7. False
8. False
9. True
10. True
11. False
12. True
B. Multiple choice p.80
1. B
2. D
3. B
4. C
5. B
6. D
7. D
8. C
9. B
10. C
11. B
12. C
13. C
14. C
15. B
C. Question p.84
1. (a) Aluminium is a conductor.
(b) It is an indicator of the presence of an electric current in the circuit. /
If the bulb lights up, the sample tested is a conductor. (any one)
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(c) (i) The bulb lights up: Iron paper clip, gold coin, pencil lead
The bulb does not light up: Glass, plastic bag, cotton ball
(ii) Iron paper clip, gold coin and pencil lead are conductors, while the others are
insulators.
(d) Connect an ammeter in series with the light bulb. The best conductor will give the
largest reading of the ammeter.
2. (a) (i)
(ii) Rheostat
(b)
(c) The reading of the ammeter decreases.
3. (a) Wire P : earth wire
Wire Q : neutral wire
Wire R : live wire
(b)
Wire of the
cooker
Wire of the
plug
P B
Q C
R A
(c) The yellow and green wire is the earth wire. It can protect people from getting an
electric shock. If there is a leakage of electric current to the metal case, and the earth
wire is not connected, a person who touches the metal case will get an electric shock.
(d) When the cooker is switched on, the electric current flowing through the cooker is
larger than 3 A . The fuse melts and breaks the circuit.
4. (a) Money saved = (0.04 – 0.003) kW × 500 h × $0.9 = $16.65
(b) Amount of electrical energy consumed = 1.5 kW × 0.5 h = 0.75 kW h
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5. (a) In parallel
(b)
(c) Total current = 100 W / 220 V + 1500 W / 220 V = 0.45 A + 6.82 A = 7.27 A
(d) (i) Total current = 7.27 A + 1300 W / 220 V = 13.18 A
(ii) The total current (13.18 A) is larger than the fuse rating (13 A), so the fuse
melts and breaks the circuit.
(iii) No. If he connects five electrical appliances of low power to the extension
unit, and if the total current that flows through the mains socket is smaller
than 13 A, they can work properly at the same time.
6. (a) (i),(ii)
Electrical
appliance
Power (W) Working
current (A)
Suitable fuse
rating (A)
Lamp 100 0.43 1
Washing machine 1400 6.09 10
Air-conditioner 1500 6.52 10
Refrigerator 200 0.87 1
LCD TV 130 0.57 1
Computer 150 0.65 1
Electric water
heater
2700 11.74 13
Iron 1000 4.35 5
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(b) (i)
Electrical
appliance
Quantity Power (W) Monthly usage
(hours)
Units of
electricity used
Lamp 7 100 200 140
Washing
machine
1 1400 50 70
Air-conditioner 3 1500 100 450
Refrigerator 1 200 720 144
LCD TV 2 130 200 52
Computer 1 150 150 22.5
Electric water
heater
1 2700 30 81
Iron 1 1000 10 10
Total units of electricity used 969.5
(ii) Total cost = (400 × $0.86) + (400 × $0.90) + (169.5 × $1.00) = $873.5
(c) (i) Air-conditioner
(ii) Replace filament bulbs with compact fluorescent lamps. (or other reasonable
answers)
Quick Review
1. Electric current, voltage and resistance p.90
(a) open
(b) closed
(c) voltage
(d) larger
(e) resistance
(f) smaller
(g) current
(h) brighter
2. Ammeter, rheostat and fuse p.90
(a) rheostat
(b) resistance
(c) fuse
(d) fuse rating
(e) broken / open
(f) fuse
(g) (electric) current
(h) black
(i) positive
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3. Series and parallel circuits p.91
(a) parallel
(b) will not
(c) will not
(d) will still
(e) will not
(f) will still
4. Socket, plug and earthing p.91
(a) earth
(b) neutral
(c) live
(d) earth
(e) neutral
(f) live
(g) live / neutral
(h) neutral / live
(i) earth
(j) earth / ground
STSE Article Reading p.92
(a) In parallel
(b) Power = 5.4 V × 0.25 A = 1.35 W
(c) It uses renewable energy. / It is environmentally friendly.
It is portable. (or any two reasonable answers)
(d) Its battery is made of materials of low resistance.
(e) The voltage and the power supplied by the charger are too small.
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Little Einstein’s Corner p.94
1. (a)
Switch 1 Switch 2 Lamp (on/off)
open open off
open closed on
closed open on
closed closed on
(b)
Switch 1 Switch 2 Lamp (on/off)
A A on
A B off
B A off
B B on
(c) Dora’s design
(d) In Paul’s design, when one switch is closed, he cannot use the other switch to turn
off the lamp.
(e)
2. (a) Resistance = 200 V / 4 A = 500
(b) Current = 220 V / 500 = 0.44 A
(c) In (a), power = 200 V × 0.4 A = 80.0 W
In (b), power = 220 V × 0.44 A = 96.8 W
(d) The bulb applied with 220 V is brighter because its power is higher.
(e) Increasing the mains voltage to 220 V can increase the power of electrical
appliances.

Chapter 7 TB Solutions

Interactive Science (Second Edition) 2A

Textbook Solutions

Chapter 7 LIVING THINGS AND AIR

Experiment 7.1A p.6-8

Part A

Observation	Test results
Observation	Oxygen	Carbon dioxide
1: colour of gas	colourless	colourless
2: smell of gas	odourless	odourless
3: change of burning splint	burns more brightly	goes out
4: change of glowing splint	relights	goes out
5: colour change of hydrogencarbonate indicator	no observable changes	changes from red to yellow
6: colour change of lime water	no observable changes	changes from colourless to milky

Part B

	Gas X	Gas Y
Test 1 (Using a glowing splint)	Result: (Answer depends on the gas and the test.)	Result: (Answer depends on the gas and test.)
Test 2 (Using hydrogencarbonate indicator / lime water)	Result: (Answer depends on the gas and test.)	Result: (Answer depends on the gas and test.)
The gas is identified as	(Answer depends on the gas in the test tube.)	(Answer depends on the gas in the test tube.)

Experiment 7.1B p.8-9

1. The paper is blue / light blue in colour.

2. (a) (i) blue / light blue

(ii) pink

(b) water

3. (a) The colour of the cobalt chloride paper changes from blue to pink.

(b) water (water vapour)

Experiment 7.1C p.9-11

Part B

	Breathed air	Unbreathed air
Time taken for burning splint to go out (s)	(Answer depends on the size of the gas jar and other conditions in the experiment.)	(Answer depends on the size of the gas jar and other conditions in the experiment.)

(a) less

(b) The splint burns for a longer time in the jar which contains more oxygen. (or other reasonable answers)

Part C

	Breathed air	Unbreathed air
Colour of hydrogencarbonate indicator after shaking	yellow	red

n Breathed air contains more carbon dioxide than unbreathed air.

Experiment 7.1D p.12

	Breathed air	Unbreathed air
Temperature (°C)	(Answer depends on the room temperature during the experiment.)	(Answer depends on the size of the gas jar and other conditions in the experiment.)

n The temperature of breathed air is higher than that of unbreathed air.

Experiment 7.1E p.13

1. (a) small droplets / moisture / a misty appearance

(b) changes from blue to pink

2. Yes, the change occurs more slowly than that in step 1.

n Breathed air contains more water vapour than unbreathed air.

SKILL Development 7.1 p.14

Discussion

1. Ben is correct and Betty is wrong, because both breathed air and unbreathed air contains more oxygen than carbon dioxide, although the oxygen content decreases and the carbon content increases in breathing.

2. Betty’s idea should be ‘breathed air contains more carbon dioxide and less oxygen than unbreathed air’.

Checkpoint 7.1 p.15

1. (a) glowing splint

(b) The glowing splints relights.

(d) The colour of the indicator changes from red to yellow.

(e) lime water

(f) dry cobalt chloride paper

(g) The colour of the paper changes from blue to pink.

2. (a) (i) more

(ii) less

E (iii) less

(iv) lower

(b) (i) less

(ii) more

E (iii) more

(iv) higher

Experiment 7.2A p.16-17

3. (a) warm

(b) heat

4. (a) A layer of mist

(b) (i) changes from blue to pink

(ii) water vapour

5. (a) changes from red to yellow

(b) carbon dioxide

Experiment 7.2B p.18-19

Part A

(a) goes out

(b) (i) liquid fuel

(ii) water

(iii) goes out

Part B

(a) goes out

(b) (i) sinks

(ii) goes out

Part C

(a) does not burn

(b) (i) heat

(ii) not high

nConclusion:

(a) fuel

(b) oxygen

Activity 7.2A p.21

1. oxygen

2. (a) Trees

(b) fuel

3. (a) heat

(b) temperature

Activity 7.2B p.22

Checkpoint 7.2 p.23

1. turning off the gas tap

2. pouring water on it

3. using a fire blanket

Experiment 7.3A p.26-27

3. (Answer depends on experimental conditions.)

7. (a) (Answer depends on experimental conditions.)

(b) (i) increases

(ii) heat

(iii) light

Experiment 7.3B p.29-30

Designing the experiment

Variable to be changed: type of snack

Variable(s) to be kept constant: initial temperature of water, volume of water, type of boiling tube, type of burning spoon

others: position and distance of burning food from the boiling tube of water (or other reasonable answers)

What to compare: increase in water temperature per gram of snack used

The results in the table:

(Answers depend on the snacks used and the experimental conditions.)

The greater the increase in water temperature per gram of snack burnt, the higher the energy content of the snack.

nConclusion:

(Answer depends on the snacks used.)

SKILL Development 7.3B p.31

1. No, Ben’s calculations and analysis are incorrect because the initial temperature is not considered.

2. In fact, C has the highest energy content and B has the lowest energy content.

The calculations are as follows:

Snack	Weight of snack used (g)	Initial water temperature (°C)	Highest water temperature reached in burning (°C)	Increase in water temperature (°C)	Increase in water temperature per gram of snack used (°C)
A	5.0	15	50	50-15=35	35/5.0=7.0
B	4.0	15	42	42-15=27	27/4.0=6.75
C	6.0	15	60	60-15=45	45/6.0=7.5

Activity 7.3 p.31-33

1. kilojoules (kJ) and kilocalories (kcal)

2. (a) 35

(b) 63

(d) 384

(e) 520

(f) 109.8

(g) 250

(h) 314.3

3. instant noodles, cakes, potato chips, sausages

4. when we have to do physical activities for a long time (or other reasonable answers)

5. We may become overweight and have greater risks of suffering from coronary heart disease, high blood pressure, diabetes, strokes, etc. (or other reasonable answers)

Checkpoint 7.3 p.34

1. (a) chemical

(b) respiration

E 2. No, he is wrong because he should compare the amounts of energy provided by the same mass of different foods.

Experiment 7.4A p.36

1. brown

3. (a) dark blue

(b) brown

n (a) brown

(b) dark blue

Experiment 7.4B p.37-38

3 (a) (i) pale green

(ii) green

(b) soft

4 (a) dark blue

(b) starch

Discussion

1. c

2. d

3. b

4. a

Experiment 7.4C p.39

5. (a) The glowing splint relights.

(b) Oxygen is present in the bottle.

Experiment 7.4D p.41-45

Identifying the problem

What are the conditions necessary for photosynthesis to take place?

Making hypotheses

(a) necessary

(b) necessary

Part A

Designing the experiment

Variable to be changed: type of snack

Variable(s) to be kept constant: type of leaf used, light source, amount of light, temperature, presence of carbon dioxide, water supply, others: (any reasonable answers)

What to compare: presence of starch in the leaf

Carrying out the experiment

3. (Drawing depends on the leaf used.)

4. (a) (Drawing depends on the leaf used.)

(b) (i) present

(ii) absent

Drawing a conclusion

Chlorophyll is necessary for photosynthesis to take place.

Part B

Variable to be changed: presence of carbon dioxide

Variable(s) to be kept constant: type of the leaf used, presence of chlorophyll, light source, water supply, temperature, amount of light

What to compare: presence of starch in the leaf

Carrying out the experiment

1. Destarch

2. bright light

3. iodine

(a) Leaf A is brown in colour and leaf B is dark blue in colour.

(b) Starch is absent in leaf A but present in leaf B.

Drawing a conclusion

Carbon dioxide is necessary for photosynthesis to take place.

Part C

Designing the experiment

Variable to be changed: presence of light

Variable(s) to be kept constant: type of the leaf used, presence of chlorophyll, water supply, temperature, presence of carbon dioxide

What to compare: presence of starch in the leaf

2. (labelled drawing of any appropriate set-up with the materials and apparatus provided)

Carrying out the experiment

1. Destarch

2. bright light

3. iodine

(a) The part of the leaf exposed to light is dark blue, and the part not exposed to light is brown.

(b) Starch is present in the part exposed to light but absent in the part not exposed to light.

Drawing a conclusion

Light is necessary for photosynthesis to take place

GLOBAL & CHINA p.45

There are large areas of tropical rainforests in South America and Central Africa. They situate around the equator. The intensity of sunlight is strong and there are long periods with sunshine. Photosynthesis is carried out by plants at high rates for long durations.

Checkpoint 7.4 p.46

(a) chlorophyll

(b) light

(d) carbon dioxide

(e) starch

(f) oxygen

Let’s Think p.47

The characteristics of food chains are:

(a) The first members are green plants. They start the food chain by converting light energy from the sun into chemical energy in food synthesized through photosynthesis.

(b) The second members are animals that feed on green plants.

Experiment 7.5A p.48-50

2. (a) (i) oxygen

(ii) carbon dioxide

(iii) carbon dioxide

(iv) decreases

(v) towards

(b) (i) also

(ii) grasshoppers

3. (a) at night

(b) in the daytime

5. (a) the same as 2(a) on p.48

(b) the same as 2(b) on p.48

6. The grasshopper takes in oxygen and releases carbon dioxide in both bright and dark conditions. The gaseous exchange of the grasshopper is similar / the same day and night.

Experiment 7.5B p.51-52

1. (a) A and C

(b) B and D

Set-up	Colour of hydrogencarbonate indicator
Set-up	at the beginning	after one hour
A	red	purple
B	red	yellow
C	red	red
D	red	red

4. (a) It shows that a green leaf takes in carbon dioxide under a bright condition.

(b) It is a control experiment for set-up A. It shows that the change in set-up A is due to the leaf.

5. (a) It shows that a green leaf releases carbon dioxide under a dark condition.

(b) It is a control experiment for set-up B. It shows that the change in set-up B is due to the leaf.

Conclusion:

(a) carbon dioxide

(b) carbon dioxide

SKILL Development 7.5B p.54

1. No, because there may be a lot of micro-organisms on rotten leaves. The gaseous exchange of the micro-organisms may affect the results of the tests.

2. Use the same set-up without a leaf.

Checkpoint 7.5A p.54

1. (a) yellow

(b) grasshopper

(d) (i) die

(ii) oxygen

2 (a) The indicator changes from red to purple.

(b) The indicator changes from red to yellow.

Checkpoint 7.5B p.56

(a)

E (b) burning fuels in