WAEC GCE Chemistry Past Questions and Answers pdf

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WAEC GCE Chemistry Past Questions pdf

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WAEC GCE Chemistry Past Answers

Below are the answers to the above questions:

Question 1 Answer

(1ai)
Mole is the amount of substance of a system which contains as many elementary entities as there are atoms in 0.012 kilogram of carbon 12. its symbol is MOL.

(1b)
(CHOOSE ONLY ONE)
(i) Incomplete combustion i.e less oxygen for combustion produces a mix of carbon, carbon dioxide, carbon monoxide and water.
(ii) Carbon monoxide (CO) & Carbon particles (soot)

(1c)
(i) Dispersion (weak).
(ii) dipole-dipole (medium).
(iii) hydrogen (strong).

(1d)
Brownian motion refers to the random movement displayed by small particles that are suspended in fluids. It is commonly referred to as Brownian movement”. This motion is a result of the collisions of the particles with other fast-moving particles in the fluid.

(1e)
Condensation Polymerization: It is form of a step-growth polymerization where smaller molecules or monomers react with each other to form larger structural units (usually polymers) while releasing by-products such as water or methanol molecule. The by-products are normally referred to as condensate.

(1f)
(i) 2-methyl propane.
(ii) 3-Chlorobutanoic acid.

(1g)
(i) The oxidation number of iodine in the potassium periodate molecule is 7.
This molecule is ionic which means that the periodate ion has a charge of 1- in order to balance the 1+ charge on the potassium ion.

Since the oxygen molecules combine for an oxidation number of 8 (4×2=8) this gives us a total oxidation number of 8−1=7

(ii) Let, X be the oxidation state of bromine in HBrO

+1 + X + (-2) = 0
1 + X − 2 = 0
X − 1 = 0
X = + 1
Hence, the oxidation state of Br in HBr03 is +1

(1h)
(i) Cathode rays consist of negatively charged particles. When cathode rays are subjected to an electrical field, these get deflected towards the positively charge plate i.e. Anode.

We know that a positively charged body would attract only a negatively charged body, therefore the particles of cathode rays carry negative charge.

Cathode rays also get deflected when these are subjected to a strong magnetic field. The electrons in the cathode rays would deflect toward the positively charged plates, and away from the negatively charged plates.

(ii) It shows that cathode rays consist of material particles having mass and velocity.

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Question 3 Answer

(3ai)
Electrode potential is defined as the potential of a cell consisting of the electrode acting as a cathode and the standard hydrogen electrode acting as an anode. Reduction always takes place at the cathode, and oxidation at the anode.

(3aii)
(Pick Any TWO)
(i) It is used to measure the relative strength of different oxidants and reactants.
(ii) It is used to predict if certain chemical species will react with each other and to what extent that reaction will be.
(iii) It is used to predict the point of equilibrium in a chemical reaction.

(3bi)
The law of constant composition, also known as the law of definite proportions, states that a given chemical compound always contains the same proportion by mass of its constituent elements, regardless of the source of the compound or the method used to prepare it.

(3ci)
Na>Mg>Al

(3cii)
(I) Na
(II) Al

(3d)
When PbCl2 is placed in water, the water molecules surround the Pb2+ and Cl- ions and break apart the ionic lattice of the solid. However, the intermolecular forces between the water molecules and the Pb2+ and Cl- ions are not strong enough to overcome the strong electrostatic attraction between the Pb2+ and Cl- ions.

PbCl2(s) ⇌ Pb2+(aq) + 2Cl-(aq)

When concentrated HCl is added to the PbCl2, the Cl- ions from the HCl react with the Pb2+ ions in the PbCl2.
PbCl2(s) + 2HCl(aq) → PbCl4^2-(aq) + 2H+(aq)

(3ei)
One of the main reasons for classifying organic compounds by their functional groups is that it also classifies their chemical behavior.

(3eii)
Ethene gas, C2H4, reacts with water at high temperature to yield ethyl alcohol, C2H6O.

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Question 4 Answer

(4ai)
To start the process of preparation of oxygen in a laboratory, hydrogen peroxide is poured into a container that is conical in shape and contains some manganese oxide inside it. After that, the gas which comes out of it is collected in another container that is upside down and filled with water. Once the oxygen reaches the container filled with water, it pushes the water out of the container and the oxygen remains inside. This gas collecting container can also be substituted with a gas syringe to collect the oxygen produced by this method.

(4bii)
i) the bleaching action of sulphur (iv)oxide is temporary while that of chlorine is permanent

ii) the bleaching action of sulphur(iv)oxide is a reduction process while that of chlorine is oxidation

(4c)
i: downward delivery
ii: ammonia and hydrogen chloride gas
iii:high solubility (in ammonia)

4civ) The aim of the fountain experiment is to prove that HCI is highly soluble in water.

4cv)
i) because It is heavier than oxygen and covers the fire like a blanket which cut off the contact between the fuel and oxygen.

(ii) It can be used for extinguishing fire involving electrical equipments and inflammable materials like petrol.

4d)
(4NH)3(g) + SO2(g) –––> 4NO(g)+ (6H)2 O(l)

2NO(g) + O2(g) ––—> 2NO2(g)

2H2O(l) + 4NO2(g) + O2(g) —––> 4HNO3(aq).