Question

1. (a) What is a transition element?
(b) Consider the electron configuration of the following elements: A = 2:8:6; B = 2:8:2; C = 2:8:1; D = 2:8:8. State the element which forms:
 (i) a double charged cation;
 (ii) a soluble trioxocarbonate (IV).
(c) Explain briefly why there is a general increase in the first ionization energies of the elements across a period in the periodic table.
(d) Give two examples of an aliphatic compound.
(e) Explain briefly why alkanols are stronger bases than water.
(f) State the major raw materials used in the Solvay process.
(g) What is geometric isomerism?
(h) Give a reason why water gas is a better fuel than producer gas.
(i) Define the term heat of combustion.
(j) (i) State Faraday's second law of electrolysis.
 (ii) Calculate the amount of silver deposited when 10920 coulombs of electricity is passed through a solution of a silver salt. [IF = 96500 C mol⁻¹]

Accepted Answer

(a) A transition element is one which has an incompletely filled d-orbital.

(b)(i) B — it has two valence electrons which can be lost on oxidation to form a doubly charged cation (B²⁺).
(ii) C — soluble trioxocarbonates (IV) are prepared by bubbling carbon (IV) oxide through a solution of the corresponding alkali of a Group 1 metal; C (2:8:1) is in Group 1.

(c) Across a period (left to right), there is a gradual increase in the number of protons in the nucleus (nuclear/effective charge). This increases the force of attraction between the nucleus and the electrons, so more energy is needed to remove the outermost electron — hence ionization energy increases.

(d) Examples of aliphatic compounds: methane, ethene, ethyne, ethanol, ethanoic acid (any two).

(e) Alkanols are stronger bases than water because of the electron-donating (positive inductive) effect of the alkyl group, which increases the electron density on the oxygen atom, making the lone pair more available to accept a proton.

(f) Major raw materials for the Solvay process: sodium chloride (brine) and limestone (calcium carbonate). [Note: The Solvay process is the industrial method for manufacturing sodium carbonate (Na2CO3) from brine and limestone.]

(g) Geometric isomerism is the existence of two compounds with the same molecular formula but which differ in the arrangement of groups attached to the carbon atoms of a double bond.

(h) Water gas (CO + H2) is a better fuel than producer gas because both of its components (CO and H2) are combustible, giving it a higher calorific/heat value than producer gas.

(i) Heat of combustion is defined as the heat change/released when 1 mole of a substance is completely burnt in excess oxygen (or completely burnt in air).

(j)(i) Faraday's second law of electrolysis states that when the same quantity of electricity is passed through different electrolytes, the relative numbers of moles of the elements discharged are inversely proportional to the charges on the ions of the elements.
(ii) Ag⁺ + e⁻ → Ag(s). 96500 C liberates 1.0 mol of Ag(s). ∴ 10920 C will liberate 10920/96500 = 0.113 mol of silver.

WAEC Chemistry 2023 Theory — Question 2

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