Key Stage 3 Science Book 2 Assessments
Explaining Chemical Changes (Blue level)
Answers
1. Which of the following turns litmus solution red? [1 mark]
b)
Difficulty level: easy
Skill level: knowledge
2. There are several clues that a chemical reaction has happened. Which two of the following
observations are true for the reaction of any acid with any reactive metal? [1 mark]
a), c)
Difficulty level: easy
Skill level: knowledge
3. Choose two reasons why putting a fire blanket over a small fire is a good way of dealing with it. [2
marks]
a), b)
Difficulty level: moderate
Skill level: application
4. Look at this picture of a metal reacting with an acid. What evidence is there that a reaction is taking
place? (2 marks)
(the answer should include the following)
1) Bubbles of gas appearing
2) Over time, the amount of metal visible will decrease.
Difficulty level: moderate
Skill level: evaluation
© HarperCollinsPublishers 2014
Key Stage 3 Science Book 2 Assessments
5. Stacey has made an indicator by boiling onion skins in water and filtering the mixture to provide a
liquid. Describe how she could then test her indicator to see how well it works. [4 marks]
(the answer should include 4 of the following)
1) She could test it in a variety of solutions
2) Include acids and alkalis of different strengths
3) Observe what colours they turn
4) Record the colour changes in different strengths of acid and alkali
Difficulty level: moderate
Skill level: application
6. Describe the pH changes when an acid is neutralised by adding alkali to it. [2 marks]
(the answer should contain the following)
1) Before mixing, acid has a pH lower than 7 and alkali a pH of higher than 7.
2) Adding the alkali to the acid increases the pH and, when neutralised, the solution has pH 7
Difficulty level: moderate
Skill level: application
7. Describe what you would see if a piece of magnesium ribbon was put into dilute hydrochloric acid. [2
marks]
(the answer should contain the following)
1) The mixture fizzes (a gas is given off)
2) The product dissolves (a colourless solution is produced)
Difficulty level: easy
Skill level: knowledge
8. Describe how coal is used to produce electricity. [2 marks]
(the answer should contain the following)
1) Coal is burned in power stations to heat water to boiling, producing steam
2) The steam turns a turbine to generate electricity
Difficulty level: moderate
Skill level: knowledge
9. Explain the difference between the terms ‘common salt’ and ‘salt’. [2 marks]
(the answer should contain the following)
1) Common salt is sodium chloride; this is just one example of a salt
2) However, a salt is produced when any acid and alkali undergo a neutralisation reaction; vast numbers
of different salts are known
Difficulty level: easy
Skill level: knowledge
© HarperCollinsPublishers 2014
Key Stage 3 Science Book 2 Assessments
10. Tom tests a clear liquid in the lab with universal indicator solution, which turns green. He says that
this shows that the liquid is neutral, water and safe to drink. Is he right? [4 marks]
(the answer should contain the following)
1) He is correct that the liquid is neutral
2) He is incorrect to say that it’s water as many liquids are neutral
3) He is incorrect to say that it’s safe – even it is water, it could have somehow dissolved in it (that had
not changed the pH)
4) In any case, drinking liquids from a lab is not safe
Difficulty level: moderate
Skill level: knowledge
11. Calcium carbonate is added to hydrochloric acid in a flask on a balance. As time passes, the mass is
recorded and displayed on a graph. The graph is shown below. Explain what is happening and why. [4
marks]
(the answer should contain the following)
1) A reaction is taking place
2) Carbon dioxide is being released
3) As gas is released, so the mass decreases
4) Gradually, less gas is released and the mass settles down to a lower level
Difficulty level: hard
Skill level: evaluation
12. Explain why combustion can lead to air pollution. [4 marks]
(the answer should contain the following)
1) Fossil fuels are burned in power stations and in various forms of transport, e.g. cars, lorries and
planes
2) Some fossil fuels contain sulfur impurities; when impure fossil fuels are burned, sulfur dioxide is
produced and becomes acid rain
3) Nitrogen oxides form when nitrogen in the air is oxidised during combustion
4) Sulfur dioxide and nitrogen oxides lead to acid rain
Difficulty level: moderate
Skill level: knowledge
© HarperCollinsPublishers 2014