BECE JHS
Acids and bases are chemical opposites. When they react, they form a salt and water.
An acid tastes sour and has a pH below 7. It turns blue litmus red. A base tastes bitter and feels soapy, and a soluble base has a pH above 7. It turns red litmus blue. A base that dissolves in water is an alkali. pH 7 is neutral. You never taste a chemical in the laboratory. Those taste descriptions come from safe household examples, such as lemon juice for a weak acid, not from bottles on the bench.
A salt is the compound formed when the hydrogen of an acid is replaced by a metal or by ammonium. Neutralisation is acid plus base giving salt plus water. An acid also reacts with a carbonate to give a salt, water and carbon dioxide. The carbon dioxide turns limewater milky. Hydrochloric acid and sodium hydroxide give sodium chloride and water. The salt you eat is that same sodium chloride, made for the table, not taken from a laboratory reaction.
Quote a test, not a colour you hope is right. Blue litmus turns red in acid. Red litmus turns blue in alkali. Name the salt from the acid and the base: hydrochloric acid gives chlorides, sulphuric acid gives sulphates, and nitric acid gives nitrates. The metal part comes from the base or the carbonate. Carbon dioxide is the gas from a carbonate, shown with limewater.
These are practice questions in the style of the paper, with a model answer and a mark scheme. They are not a promise of what your paper will ask.
4 marks
(a) State the colour of blue litmus in a dilute acid. (1 mark)
(b) State what pH 7 means. (1 mark)
(c) Complete: acid + base → ________ + ________ (2 marks)
(a) Red.
(b) Neutral.
(c) Salt and water.
4 marks
Dilute hydrochloric acid is added to solid calcium carbonate.
(a) Name the gas given off. (1 mark)
(b) Describe a test for the gas, and state the result. (2 marks)
(c) Name the salt formed. (1 mark)
(a) Carbon dioxide.
(b) Bubble the gas through limewater. The limewater turns milky.
(c) Calcium chloride.
4 marks
Explain the difference between a base and an alkali, and give one example of each. (4 marks)
A base neutralises an acid. An alkali is a base that dissolves in water. Copper oxide is a base that does not dissolve. Sodium hydroxide dissolves, so it is an alkali.
More questions on this topic are inside GLearn, marked as you answer, with the reason written out. The first ones need no account.
Practise Science freeIt is the reaction of an acid with a base to form a salt and water. The pH moves towards 7. An acid with a carbonate also makes a salt and water, and it makes carbon dioxide as well.
Hydrochloric acid gives chlorides, sulphuric acid gives sulphates, and nitric acid gives nitrates. The other part of the name comes from the metal in the base or the carbonate. Hydrochloric acid with sodium hydroxide gives sodium chloride. All BECE Science past questions