Waec Chemistry 2003 Past Questions and Answers

Question 36:

• WAEC 2003

When a sample of water was boiled, it lathered more readily with soap. it can be concluded that the sample most likely contained

A. Magnesium tetraoxosulphate (VI)
B. Suspended solids
C. Organic impurities
D. Calcium hydrogentrioxocarbonate (IV)

Question 37:

• WAEC 2003

What are the two gases associated with the formation of acid rain?

A. CO₂ and HCI
B. CO₂ and N₂
C. CO₂ and NO₂
D. HCI ans SO₂

Question 38:

• WAEC 2003

Which of the following processes will pollute water?

A. Exposure of a body of water ultraviolet rays
B. Discharge of industrial effluents effluents into water ways
C. Passage of river water through a send bed
D. Addition of a measured quantity of chlorine to water

Question 39:

• WAEC 2003

(a) The electronic configuration of five elements represented by the letters P, Q, R, S and T are indicated below.
P - 1s\(_2\)2s\(_2\)2p\(_2\)
Q 1s\(_2\)2s\(_2\)2p\(_4\)
R 1s\(_2\)2s\(_2\)2p\(_6\)
S - 1s\(_2\)2s\(_2\)2p\(_6\)3s\(_2\)
T - 1s\(_2\)2s\(_2\)2p\(_6\)3s\(_2\)3p\(_5\)

without identifying the elements, state which of them
(i) belongs to group VI in the periodic table;
(ii) is strongly metallic in character;
(iii) readily ionizes by gaining one electron;
(iv) contains two unpaired electrons in the ground state atom
(v) readily loses two electrons during chemical bonding
(vi) Does not paricipates in chemical reactions?
(vii) is an s-block element.

(b)(i) Copy and complete the table below as appropriate

Particle	Number of Protons	Number of Electrons	Number of Neutrons
\(^1_1H\)	1	1
\(^{27}_{13}\)Al\(^{3+}\)
\(^{16}_{8}O^{2+}\)			8

(ii) Give the reason why atomic radius increases down a group in the periodic table but decreases from left to right in a period.

(c)(i) What is meant by the half-life of a radioactive element?
(ii) The nuclide \(^{210}_{84}PO\) loses an alpha 4° particle to form lead. Write an equation for the reaction.

(d) State the type of chemical bonding which accounts for each of the following observations:
(i) Chlorine exists as discrete molecules
(ii) Sodium chloride dissolves readily in water;
(iii) CuSO\(_{4(aq)}\) forms a deep blue complex ion with excess NH\(_{3(aq)}\)

Question 40:

• WAEC 2003

(a) (i) State three characteristic properties of transition metals.
(ii) What is the oxidation state of manganese In each of the following species? (1) MnCl\(_2\) (II) MnO\(_2\) (III) MnO\(_4^{-}\)
(iii) Explain why manganese conducts electricity in the solid state but manganese chloride conducts only when molten or in solution.

(b)(i) The collision theory suggests that for two particles to react, they must collide. What two factors determine whether or not the collision would lead to formation of products?
(ii) Use an energy profile diagram to illustrate what is meant by the enthalpy change (\(\Delta\)H) and the activation energy (E\(_A\)) of a reaction.

(c) When few drops of aqueous KSCN are added to a solution of iron (III) salt the following equilibrium is set up:
Fe\(^{3}_{(aq)}\) + 3SCN\(^{-}_{(aq)}\) \(\rightleftharpoons\) Fe(SCN)\(_{3(aq)}\)
yellow colourless deep red
The equilibrium mixture has a pale red colour.
(i) Explain what would happen if more KSCN\(_{(aq)}\) were added to the equilibrium mixture.
(ii) Which of the ions in the equilibrium mixture forms an insoluble hydroxide with NaOH\(_{(aq)}\)? Write an equation for the reaction
(iii) State two changes observed on adding NaOH\(_{(aq)}\) to the equilibrium mixture.