Chapter 10 WB Solutions

Interactive Science (Second Edition) Workbook Solutions
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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