Waec Chemistry 2024 Expo Answer

Welcome to “Naijaclass Academy” For Waec Chemistry 2024 Expo Answer

Date: Wednesday, 22nd May, 2024
Chemistry (Essay & Objective) 9:30 am – 12:30 pm.



Chemistry Objectives



Answer all

Number (1) is complete

Answer only 3

Number (2) is complete
Number (4) is complete
Number (5) is complete

An electrochemical cell is a device that converts chemical energy into electrical energy or vice versa. It consists of two half-cells, each containing a electrodes (an anode and a cathode) immersed in an electrolyte, which facilitates the flow of ions between the electrodes.

(i)Spontaneity: Electrochemical cells are spontaneous, meaning they generate electricity on their own, while electrolytic cells require an external power source to drive the reaction.
(ii)Direction of Electron Flow: In electrochemical cells, electrons flow from the anode to the cathode, while in electrolytic cells, electrons flow from the cathode to the anode.
(iii)Purpose: Electrochemical cells are used to generate electricity, while electrolytic cells are used to drive non-spontaneous reactions, such as electroplating or water splittings.

(i)The blue color of the copper sulfate solution starts to fade as zinc replaces the copper.
(ii)Solid copper begins to precipitate out of the solution, forming a reddish-brown deposit at the bottom of the beaker.
(iii)The solution might gradually become colorless if all the copper ions are replaced.
(iv)Bubbles of hydrogen gas may be observed if the zinc is in excess, indicating the occurrence of further reactions involving the zinc and the sulfate or the acidic solution.

CH4(g) -> C(s) + 2H2(g)

Decomposition reaction

(i) hydrogen chloride (HCl)
(ii)sulfur dioxide (SO2).

(i)high temperature
(ii)presence of a catalyst
(iii)longer hydrocarbon chain length.

Noble gases are chemically inert because they have a completely filled outer shell of electrons, making them very stable and unlikely to react with other elements.

(i)Members have the same general formula
(ii)Members have similar chemical properties
(iii)Members have a gradual change in physical properties
(iv)Members have a constant difference in molecular formula between successive members

Global warming refers to the long-term rise in the average surface temperature of the Earth due to the increasing levels of greenhouse gases in the atmosphere.

increasing levels of carbon dioxide (CO2) in the atmosphere, primarily due to fossil fuel burning, deforestation, and land-use changes.

I. Direct combination of constituent elements:
The direct combination reaction involves lead and chlorine gas.
Pb(s)+Cl₂(g) —> PbCl₂(s)

II. Double decomposition:
The double decomposition reaction can be achieved by reacting lead (II) nitrate with sodium chloride.
Pb(NO₃)₂(aq)+2NaCl(aq) —> PbCl₂(s)+2NaNO₃(aq)

III. Displacement reaction:
The displacement reaction can be achieved by reacting lead with hydrochloric acid.
Pb(s)+2HCl(aq) —> PbCl₂(s)+H₂(g)

I. Direct combination of constituent elements:
Increasing the temperature would increase the rate of reaction. Higher temperatures provide more kinetic energy to the reacting particles, increasing the chances of successful collisions.

II. Double decomposition:
Increasing the concentration of the reactants (lead (II) nitrate and sodium chloride) would increase the rate of reaction. Higher concentrations lead to more frequent collisions between reacting particles.

III. Displacement reaction:
Increasing the surface area of lead by using powdered lead instead of a solid block would increase the rate of reaction. A greater surface area allows more reactant particles to collide simultaneously.

-Increase Pressure: According to Le Chatelier’s Principle, increasing the pressure of the system will favor the formation of
SO₃ since there are fewer moles of gas on the product side (3 moles of reactants vs. 2 moles of products).

-Decrease Temperature: Since the reaction is exothermic (∆H is positive), decreasing the temperature will favor the forward reaction, thus increasing the yield of SO₃

First, determine the limiting reactant by comparing the mole ratio:

From the balanced equation:
2 volumes of SO₂ react with 1 volume of O₂

SO₂= 60 cm³
O₂= 40 cm³

Required O₂=60cm³/2= 30cm³

Since 30cm³ of 02 is required but 40cm³ is available, SO₂ is the limiting reactant.

Volume of SO₃ formed: 60cm³SO₂ —> 60cm³SO₃.

Volume of residual O₂:
Initial O₂ – Reacted O₂ = 40cm³ – 30cm³

Total residual gas volume:
Residual O₂=10cm³

-Oxidation number of sulfur in SO₂: +4
-Oxidation number of sulfur in SO₃: +6

Change in oxidation number:
+6-(+4)= +2


Cyclopropane has the molecular formula C3H6 with a ring structure WHILE n-Propane has the molecular formula C3H8 with a linear structure.

-Compound X: Propanol (or specifically, 1-propanol)
-Compound Y: Propyl butanoate

hydroxyl group (-OH)

CH₃H₇OH +CH₄H₈O₂ —> C₇H4O₂ +H₂O












Leave a Reply

Your comment are Monitored.