2023 - JAMB Chemistry Past Questions and Answers - page 7

A unique property of water compared to other liquids is that it expands when freezing.

Unlike most substances, water expands as it freezes, leading to the formation of ice with a lower density than liquid water.

The main environmental concern associated with sulfur dioxide (SO₂) emissions is the formation of acid rain.

When sulfur dioxide reacts with water vapour in the atmosphere, it forms sulfuric acid, contributing to the acidity of rainwater and causing environmental issues such as soil and water pollution.

Anhydrous cobalt chloride paper is blue. When it is exposed to water or moisture, it undergoes a reversible chemical reaction with water.

This reaction leads to the formation of hydrated cobalt chloride, which is pink.

Therefore, the colour change observed when anhydrous cobalt chloride paper comes into contact with water is from blue to pink. This property is often used as an indicator for the presence of moisture or humidity in a given environment.

Eutrophication is the excessive growth of algae and other aquatic plants in a water body, often caused by an increase in nutrients such as nitrogen and phosphorus.

This process can lead to imbalances in the ecosystem, depletion of oxygen, and negative impacts on other organisms in the water.

Chromatography is the separation technique used to separate different pigments in a mixture based on their affinity for a stationary phase and a mobile phase.

The pigments are carried by the mobile phase (usually a solvent) through a stationary phase (a solid or liquid adsorbent), resulting in the separation of individual components based on their interaction with the stationary and mobile phases.

To calculate the mass percentage of carbon in methane (CH₄), you need to consider the molar mass of carbon and methane.

The molar mass of CH₄:
Carbon (C) has a molar mass of approximately 12 g/mol.
Hydrogen (H) has a molar mass of approximately 1 g/mol.
Therefore, the molar mass of CH₄ = 12 g/mol (C) + 4 g/mol (H) = 16 g/mol.

The mass percentage of carbon in CH₄ is calculated as follows:
(12 g/mol / 16 g/mol) × 100% = 75%

Sodium reacts vigorously with water to produce sodium hydroxide (NaOH) and hydrogen gas (H2).

The chemical equation for this reaction is:

\[ 2 \, \text{Na} + 2 \, \text{H}_2\text{O} \rightarrow 2 \, \text{NaOH} + \text{H}_2 \]

The product of the electrolysis of aqueous sodium chloride (NaCl) using inert electrodes is hydrogen gas (H₂) at the cathode and chlorine gas (Cl₂) at the anode.

The overall reaction can be represented as follows:

\[ 2 \, \text{H}_2\text{O} + 2 \, \text{NaCl} \rightarrow \text{H}_2 \uparrow + \text{Cl}_2 \uparrow + 2 \, \text{NaOH} \]

Hydrogen gas is produced at the cathode, and chlorine gas is produced at the anode.

The noble gas that is radioactive and is produced as a decay product of uranium and thorium is Radon (Rn).

The decomposition of hydrogen peroxide (H₂O₂) into water (H₂O) and oxygen (O₂) is an example of an endothermic reaction. In this reaction, energy is absorbed to break the bonds in hydrogen peroxide, leading to the formation of water and oxygen.