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1. What are indicators used for? (lesson 6a)
2. What colour does litmus go in acid? (6a)
3. What can you use to crush up a plant to extract the colour. ? (6a)
4. Why is universal indicator more useful that other indicators? (6b)
5. What is the pH number of a neutral solution? (6b)
6. Sodium hydroxide has a pH of 14. What does this tell you about sodium hydroxide? (6b)
7. What would be the pH of strong acid? (6b)
8. How does acid affect limestone? (6b)
9. What is the missing word? Acid + ------ = a neutral solution. (6c)
10. What causes indigestion? (6c)
11. How do indigestion tablets work? (6c)
12. Why is toothpaste usually slightly alkaline? (6c)
13. How can farmers change the pH of acidic soil? (6d)
14. How would you test the pH of some soil? (6d)
15. Which plants grow well in slightly alkaline conditions. Use the table on page 80 to help you. (6d)

ANSWERS

1. To show which substances are acids and which are alkalis.
2. red (pink).
3. A mortar and pestle.
4. Because it shows how or weak an acid or alkali is.
5. 7.
6. It is a strong alkali.
7. 1.
8. It reacts wearing away the rock.
9. Alkali.
10. Too much acid in the stomach.
11. They neutralise excess acid.
12. So it can neutralise the acids that cause tooth decay.
13. By adding lime (an alkali).
14. Add distilled water, filter then add universal indicator to the filtrate.
15. Mint and blackcurrant.