Chemistry Past Questions and Answers

Benzene contains six carbon atoms and six hydrogen atoms.
(a)(i) Draw two stable structures of benzene to show how these atoms are arranged.
(ii) What is the concept behind these structures?
(b) Give (i) two uses of benzene. (ii) one industrial source of benzene.

(a) Arrange the first three members of the halogen family in their increasing order of electronegativity. Give the reason for your answer.
(b) State and explain what happens when chlorine reacts with starch iodide paper.

(a) Name the type of solid structure possessed by:
(i) diamond;
(ii) iodine;
(iii) sodium chloride.

(b) Give:
(i) one alloy of tin:
(ii) a common reducing agent which is a compound of tin.

Liquefied air is mainly a mixture of nitrogen and oxygen which can be separated into its components by fractional distillation (Boiling point of nitrogen is 196°C, Boiling point of oxygen is 174°C)
(a) Name the fraction which distills over first. Give the reason for your answer.
(b) Give another industrial application of fractional distillation as a separation technique.

(a)(i) List two physical properties used as criteria for purity of substances
(ii) describe how you would prepare a pure, dry sample of sodium chloride crystals by a neutralization reaction, using bench reagents.
(iii) Give two other general methods for preparing soluble salts.

(b) Explain the following observations:
(i) a sheet of iron placed in dilute copper (II) tetraoxosulphate (VI) solution reddish brown;
(ii) the white gelatinous precipitate formed when a few drops of sodium hydroxide solution are added to a solution of aluminium salt dissolves in excess alkali;
(iii) the pale green prepared iron(II) chloride solution changes to brown on bubbling chlorine gas through it.
(iv) Write a balanced equation for the reaction of dilute hydrochloric acid with marble. List two industrial process in which limestone is used as a raw material.