Chemistry Past Questions | West African Examinations Council (WAEC)

Question 21

A compound with molecular formula CH₂O₂ is

Options

A) A Carbohydrate

B) A Carboxylic acid

C) An alkanol

D) An ester

The correct answer is B.

Explanation:

Looking at the Structural formula of Ethanoic acid:
HCOOH which is also CH₂O₂

Question 22

The quantity of electricity required to discharge 1 mole of univalent ion is

Options

A) 9600 C

B) 48250 C

C) 96500 C

D) 193000 C

The correct answer is C.

Explanation:

The quantity of electricity required to discharge 1 mole of univalent ion is approximately 96500 C.

Question 23

Chlorine water is used as a bleaching agent because it is

Options

A) An acidic solution

B) An alkaline solution

C) An oxidizing agent

D) A reducing agent

The correct answer is C.

Question 24

Which of the following substances is a non-electrolyte?

Options

A) H₂SO₄

B) CH₃COOH

C) C₆H₁₂O₆

D) NH₄Cl

The correct answer is C.

Explanation:

Sugar solution isn't an electrolyte. The compound C₆H₁₂O₆ is glucose which is also sugary.

Question 25

The oxidation number of sulphur is +4 in

Options

A) Na₂S₂O₃

B) H₂SO₃

C) H₂SO₄

D) SO₃

The correct answer is B.

Explanation:

$H_{2}S{O}_3$

$(+1\times 2)+\text{S}+(-2\times 3)=0$

$2+\text{S}-6=0$

$-4+\text{S}=0$

TO GET S ADD +4 TO THE BOTH SIDES:

$-4+4+\text{S}=0+4$

$\text{S}=+4$

Question 26

Consider the following ionic equation:
Cr₂O₇^2- + 14H⁺ + ne^- → 2Cr³⁺ + 7H₂O.
The value of n in the equation is _______?

Options

A) 7

B) 6

C) 3

D) 2

The correct answer is B.

Question 27

Consider the following half-cell reactions.

Al_(s) → Al³⁺_(aq) + 3e^-

Cu²⁺_(aq) + 2e^- → Cu_(s)

The overall equation for the reaction is

Options

A) Al_(s) + Cu²⁺_(aq) → Al³⁺_(aq) + Cu_(s)

B) 2Al_(s) + Cu²⁺_(aq) → 2Al_(aq) + Cu_(s)

C) 2Al_(s) + 3Cu²⁺_(aq) → 3Cu_(s) + 2Al³⁺_(aq)

D) 3Al_(s) + 2Cu²⁺_(aq) → Cu_(s) + 3Al³⁺_(aq)

The correct answer is C.

Explanation:

Al_(s) → Al³⁺_(aq) + 3e^- -------(i)
Cu²⁺_(aq) + 2e^- → Cu_(s) -------(ii)
To balance the electrons, multiply equation (i) by 2 and equation (ii) by 3 and then add the resulting equations
2Al_(s) → 2Al³⁺_(aq) + 3e^-
3Cu²⁺_(aq) + 6e^- → 3Cu_(s)
2Al_(s) + 3Cu²⁺_(aq) → 3Cu_(s) + 2Al³⁺_(aq)

Question 28

Amino acids are obtained from proteins by

Options

A) Hydrolysis

B) Oxidation

C) Polymerization

D) Reduction

The correct answer is A.

Explanation:

A peptide is a molecule composed of two or more amino acids. The bond that holds together the two amino acids is a peptide bond, or a covalent chemical bond between two compounds (in this case, two amino acids). It occurs when the carboxylic group of one molecule reacts with the amino group of the other molecule, linking the two molecules and releasing a water molecule.

Long chain polypeptides can be formed by linking many amino acids to each other via peptide bonds. The amide bond can only be broken by amide hydrolysis, where the bonds are cleaved with the addition of a water molecule. The peptide bonds of proteins are metastable, and will break spontaneously in a slow process. Living organisms have enzymes which are capable of both forming and breaking peptide bonds .

Question 29

When a compound X is heated with concentrated tetraoxosulphate (VI) acid, it produces an alkene. X is an

Options

A) Alkane

B) Alkanol

C) Alkanoate

D) Alkyne

The correct answer is B.

Question 31

The compound that makes palm wine taste sour after exposure to the air for few days is

Options

A) Ethanol

B) Ethanoic acid

C) Methanol

D) Methanoic acid

The correct answer is B.

Question 32

Which of the following compounds is/are secondary alkanols?

I) CH₃CH(CH₃)CH₃OH

Ii) CH₃CH₂CH(OH)CH₃

Iii) CH₃C(OH)(CH₃)CH₃

Options

A) I only

B) II only

C) I and III only

D) II and III only

The correct answer is B.

Question 33

Consider the following reaction equation:
C₂H_4(g) + 3O_2(g) → 2CO_2(g) + 2H₂O_(l).

The volume of oxygen at s.t.p that will be required to burn 14g of ethene is
[C₂H₄ = 28; Molar volume of gas at s.t.p = 22.4dm³]

Options

A) 64.2dm³

B) 33.6dm³

C) 11.2dm³

D) 3.73dm³

The correct answer is B.

Explanation:

C₂H_4(g) + 3O_2(g) → 2CO_2(g) + 2H₂O_(l)
1 mole of ethene required 3 moles of O₂
28g of ethene required 3 $\times$

22.4dm³ of O₂
14g will require $\frac{14\times 3\times 22.4{dm}^3}{28}$

= 33.6dm³

Question 34

Which of the following sources of energy contributes to green-house effect?

Options

A) Natural gas

B) Nuclear

C) Wind

D) Solar

The correct answer is A.

Question 35

A consequence of global warming is

Options

A) Air pollution

B) Flooding

C) Increased humidity

D) Water pollution

The correct answer is A.

Question 36

Which of the following metals is common to both brass and bronze?

Options

A) Aluminium

B) Copper

C) Lead

D) Iron

The correct answer is B.

Question 37

The alkanol obtained from the production of soap is

Options

A) Dihydric Alkanol

B) Tertiary Alkanol

C) Trihydric Alkanol

D) Monohydric Alkanol

The correct answer is C.

Explanation:

A trihydric alkanol is any of a class of alcohols that have three hydroxyl groups per molecule. It is also called trihydric alcohol.

Question 38

The negatively charged particle in an atom is the

Options

A) Electron

B) Neutron

C) Positron

D) Proton

The correct answer is A.

Explanation:

The electron is the negetively charged particle in an atom.

Question 39

How many orbits are contained in an atom with atomic number 13?

Options

A) 7

B) 6

C) 5

D) 3

The correct answer is D.

Explanation:

An orbit is a well-defined circular path followed by electron around nucleus. It represents two dimensional motion of electron around nucleus. The maximum no. of electrons in an orbit is 2n². Aluminium has three electron shells with 2, 8, 3 electrons each.

Question 40

The Van der Waals forces are dominant intermolecular forces in __________.

Options

A) Ammonium chloride

B) Chlorine

C) Sodium chloride

D) Water

The correct answer is B.

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