Waec Chemistry 1990 Past Questions and Answers

Question 36:

• WAEC 1990

A hydrocarbon X which decolorizes bromine water but has no action on ammoniacal silver trioxonitrate (V) solution was found to have a molar mass of 58 g mol\(^{-1}\)
(a) Deduce the molecular formula of X. (H = 1, C = 12)
(b) Write the structures of two isomers of X.

Question 37:

• WAEC 1990

(a) Balance the nuclear equation below and hence identify Y.
\(^{238}_{94}U \to ^{234}_{92}Th + Y\)
(b) In a tabular form, state two of the observations in the cathode ray experiment and the corresponding deductions.

Question 38:

• WAEC 1990

(a) Give one reason why a collision between reactants may not produce new species.
(b) Explain, illustrating with appropriate equation(s), why an aqueous solution of aluminium chloride is acidic.

Question 39:

• WAEC 1990

(a) Give the formula indicating the relationship between entropy, free energy and enthalpy changes of a system.
(b) For each of the following, state whether entropy change is positive, negative or zero.
(i) H\(_2\)O\(_{(g)}\) -> H\(_2\)O\(_{(g)}\)
(ii) Cl\(_{2(g)}\) ---> 2CI\(_{(g)}\)
(iii) HCI\(_{(g)}\) -> HCl\(_{(g)}\)

Question 40:

• WAEC 1990

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.