WAEC GCE 2023 CHEMISTRY (ESSAY & OBJ ) ANSWERS(12th December)

WAEC GCE 2023 CHEMISTRY (ESSAY & OBJ ) ANSWERS – EXAMKING.NET
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CHEMISTRY-OBJ
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11-20: ABBBADBBAB
21-30: CACBDCABCC
31-40: BDBDBBBADA
41-50: DAADBDBADD
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CHEMISTRY-ESSAY-ANSWERS
(1ai)
(i) Pressure: Gas pressure is the force exerted by gas particles on the walls of the container per unit area.

(ii) Volume: The amount of space occupied by a gas is its volume. This can be measured in liters or cubic meters.

(1aii)
The SI unit for pressure is Pascal (Pa).

(1b)
The formation of a sodium ion from a sodium atom is an example of oxidation because the sodium atom loses an electron, resulting in an increase in its oxidation state.

(1c)
Chlorine(I) oxide (Cl₂O) is a molecular compound held together by relatively weak forces such as Van der Waals forces or London dispersion forces. These forces are weaker compared to the strong covalent or ionic bonds found in many other compounds. The weaker intermolecular forces result in a lower melting point for chlorine(I) oxide.

(1d)
(i) Ensure that both the copper(II) oxide and the dilute trioxonitrate(V) acid used in the reaction are of high purity to avoid impurities in the final product.

(ii) Ensure that the reaction is carried out under controlled conditions (e.g., temperature, pressure) to optimize the yield and purity of copper (II) trioxonitrate (V).

(1ei)
– At the cathode (negative electrode): Copper ions (Cu²⁺) in the copper(II) tetraoxosulphate(VI) solution gain electrons and are reduced to solid copper (Cu).

– At the anode (positive electrode): Copper atoms (Cu) from the copper electrode lose electrons and oxidize into copper ions (Cu²⁺), entering the solution.

(1eii)
oxygen gas will be evolved at the anode.

(1f)
Van der Waals forces between chlorine molecules are stronger than those between fluorine molecules because chlorine atoms have more electrons, leading to a larger electron cloud. This larger electron cloud results in stronger temporary dipoles and thus stronger Van der Waals forces.

(1g)
A reversible reaction is a chemical reaction that can proceed in both the forward and reverse directions. It means that the reactants can form products, and the products can also react to form the original reactants.

(1h)
In chemistry, a postulate refers to a fundamental assumption or hypothesis that forms the basis for a theory or model. Postulates are statements accepted without direct proof but are used to derive and explain other principles or observations. They serve as starting points for building theoretical frameworks that help understand and predict chemical behavior.

(1i)
An atom of sodium has 6.02×10²³ molecules equivalent to 1 mole

No. of moles = mass/molar mass
Mass= no. of moles × molar mass
= 1 × 23
Mass = 23g

(1hi)
Graham’s law states that the rate of effusion or diffusion of a gas is inversely proportional to the square root of its molar mass.

(1hii)
The melting point of a sample of a compound is related to its purity in the sense that impurities tend to lower and broaden the melting point range. A pure substance has a sharp and well-defined melting point, while impurities introduce variability and may cause the substance to melt over a range of temperatures. Therefore, a higher degree of impurity is often associated with a lower and less sharp melting point. Melting point determination is a common method used to assess the purity of a substance
(1)

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(2)


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(4ai)
Air is a mixture of gases, primarily composed of nitrogen, oxygen, carbon dioxide, and trace amounts of other gases.

(4aii)
Nitrogen

(4aiii)
A noble gas is an element from Group 18 of the periodic table, characterized by its stable and inert nature.

(4aiv)
(i) They are chemically inert
(ii) They have a full outer electron shell
(iii ) They exist as colorless, odorless gases at room temperature.

(4bi)
(PICK ANY TWO)
(i) Calcium chloride
(ii) Sodium sulfate
(iii) Potassium hydroxide
(iv) Anhydrous calcium sulfate

(4bii)
N2 + 3H2 —-> 2NH3

(4biii)
It is often done through upward displacement of air or downward delivery into a container.

(4biv)
Differences in the method of collection of gases depend on factors such as the gas’s density, solubility, and reactivity with atmospheric components.

(4ei)
-Haematite undergoes reduction
-Coke acts as a reducing agent and provides heat.
-Limestone undergoes decomposition to form calcium oxide.

(4eii)
Cast iron is brittle and contains a higher percentage of carbon compared to wrought iron, which is malleable and has a lower carbon content.

(4eiii)
Conditions favoring the conversion of sulfur (IV) oxide to sulfur (VI) oxide include low temperature, high pressure, and the presence of a catalyst.

(4di)
Both diamond and graphite have high melting points due to the strong covalent bonds between carbon atoms in their structures. In diamond, each carbon atom forms four strong covalent bonds in a tetrahedral structure, while in graphite, carbon atoms are arranged in layers held together by weak van der Waals forces.
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(5a)
Soap is manufactured through a process called saponification. In this process, pellets of sodium hydroxide (NaOH) and vegetable oil are used as the main ingredients. First, the vegetable oil is heated, and then the heated vegetable oil is mixed with sodium hydroxide pellets. This mixture is stirred continuously until a thick, creamy consistency is achieved. This mixture is then left to cool and solidify into soap bars. The sodium hydroxide reacts with the fatty acids present in the vegetable oil, resulting in the formation of soap molecules.

(5bi)
The industrial preparation of oxygen from air involves a process called fractional distillation. Air is first compressed and cooled, causing it to liquefy. This liquefied air is then subjected to fractional distillation, a process that separates the different components of air based on their boiling points. Oxygen, which has a lower boiling point than nitrogen, is separated and collected as a pure gas.

(5bii)
(i) oxygen: Oxygen supports combustion and is necessary for a flame to burn.
(ii) Hydrogen: hydrogen is highly flammable and can readily ignite.

(5ci)
(i) Calcium hydroxide: It helps to neutralize any acidic components and improve the overall quality of the water.
(ii) Calcium: is an essential nutrient for human health and is important for the development and maintenance of strong bones and teeth.

(5cii)
(i) Natural sources
(ii) Fossil fuel extraction and combustion

(5ciii)
When sulfur reacts with iron, iron sulfide (FeS) is formed. This reaction can be represented by the equation:
Fe + S -> FeS

(5di)
The term hardness of water refers to the concentrationof dissolved minerals, particularly calcium and magnesium ions. Hard water can cause build-up and scaling in pipes and appliances, reduce the effectiveness of soaps and detergents, and can also affect the taste and odor of water.

(5dii)
2H2SO4 + 2NaCl → 2HCl + Na2SO4

(5diii)
Fe2O3 + 3CO → 2Fe + 3CO2
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