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Lesson: Chapter 7 — Acids, bases and salts

Putting the chapter together 2 of 3

The exercise

Worked answers to the chapter's exercise.

Question 1 — complete the sentences

Fill in the blanks

  1. Sodium hydroxide and ______ acid react to form sodium chloride and water.
  2. Calcium carbonate and hydrochloric acid react to release ______ gas.
  3. Potassium hydroxide and sulphuric acid react to form ______ and ______.
  4. ______ acid and ______ hydroxide react to form magnesium nitrate.
  5. ______ acid reacts with magnesium, releasing ______ gas and forming ______ magnesium chloride.

The answer

  1. Hydrochloric
  2. Carbon dioxide
  3. Potassium sulphate and water
  4. Nitric; magnesium
  5. Hydrochloric; hydrogen; the salt

Question 2 — three unlabelled solutions

You have sodium hydroxide, dilute hydrochloric acid and sodium chloride solutions, not labelled, and only blue litmus paper. How do you tell them apart?

  1. Find the acid.
  2. Tell the other two apart.

The answer

  1. Dip blue litmus in each: the one that turns it red is hydrochloric acid.
  2. Dip that red litmus paper into the other two: sodium hydroxide turns it back to blue; sodium chloride, being neutral, leaves it red.

Question 3 — choose from the list

Complete the blanks with solutions chosen from the list

H2SO4(aq), HCl(aq), NH3(aq), H2O(l), Ca(OH)2(aq), CH3COOH(aq)

  1. Red litmus is turned blue by ______ and ______.
  2. ______ and ______ act as strong acids.
  3. The pH is above 7 in ______ and ______.
  4. Vinegar used at home is dilute ______.
  5. Severe burns on the skin are caused by ______.
  6. Calcium sulphate forms from the reaction between ______ and ______.

The answer

  1. NH3(aq) and Ca(OH)2(aq)
  2. H2SO4(aq) and HCl(aq)
  3. NH3(aq) and Ca(OH)2(aq)
  4. CH3COOH(aq)
  5. H2SO4(aq), a concentrated strong acid
  6. Ca(OH)2(aq) and H2SO4(aq)

Question 4

pH, carbonates and a caterpillar

  1. Arrange in order of increasing pH: sodium hydroxide, sulphuric acid, water, vinegar.
  2. Of dilute hydrochloric acid, dilute sodium hydroxide and acetic acid, which does not react with sodium carbonate?
  3. A hairy caterpillar's sting itches and burns because of the formic acid in it. Suggest something to put on the skin to ease it.

The answer

  1. Sulphuric acid, vinegar, water, sodium hydroxide.
  2. Dilute sodium hydroxide: it is a base, and it is acids that react with carbonates.
  3. A mild base such as baking soda (NaHCO3) solution, which neutralises the acid.