2025 - JAMB Chemistry Past Questions and Answers - page 3

The rate of reaction is calculated by dividing the mass of substance consumed by the time taken.

The mass of iron that reacted is 5 g, and the time taken is 10 minutes. Since the required unit is g/hr, the time must be converted to hours.

There are 60 minutes in 1 hour, so 10 minutes is equal to \( \frac{10}{60} \) hours.

This gives \( \frac{10}{60} = \frac{1}{6} \) hour.

The rate is therefore calculated as

\[ \text{Rate} = \frac{5}{\frac{1}{6}} \]

Dividing by a fraction is equivalent to multiplying by its reciprocal, so

\[ \text{Rate} = 5 \times 6 = 30 \text{ g/hr} \]

Hence, the rate of reaction is 30 g/hr.

Tetraoxosulphate(VI) acid, commonly known as sulphuric acid, is produced industrially by a method that involves oxidation and absorption reactions.

In this method, sulphur is first burned in air to produce sulphur dioxide gas. This sulphur dioxide is then further oxidized to sulphur trioxide using a suitable catalyst. The sulphur trioxide formed is absorbed into concentrated sulphuric acid to produce oleum, which is then diluted with water to obtain sulphuric acid of the desired concentration.

This sequence of reactions and processing steps is known as the Contact process.

Therefore, the industrial method used is the Contact process.

Petroleum contains many different chemical substances combined together rather than a single pure substance.

These substances include various hydrocarbons with different molecular sizes and structures. Because the proportions of these hydrocarbons differ depending on the source and formation conditions, the overall composition is not fixed.

A pure substance has a definite and constant composition, but petroleum does not meet this condition. Instead, it consists of several components physically mixed together.

This means petroleum is classified as a mixture, and mixtures naturally have variable composition.

The equation relates pressure, volume, temperature, and amount of gas in one relationship.

The expression can be rearranged into the form

\[ PV = nRT \]

In this equation, P represents pressure, V represents volume, n represents the number of moles, R is the gas constant, and T represents temperature.

This equation combines the relationships between these variables into a single formula that describes the behavior of gases under different conditions.

Because it applies generally to gases and connects all these properties, it is known as the general gas law.

Water molecules are polar because oxygen attracts electrons more strongly than hydrogen. This creates a partial negative charge on oxygen and partial positive charges on hydrogen atoms.

Because of these opposite charges, the hydrogen atom of one water molecule is attracted to the oxygen atom of another water molecule. This attraction is called hydrogen bonding.

These hydrogen bonds hold the molecules close together and prevent them from separating easily into the gaseous state.

As a result, water remains in liquid form at room temperature due to hydrogen bonding between its molecules.

The reactants are ethanol, which is an alcohol, and ethanoic acid, which is a carboxylic acid.

When these two substances react, they combine to form ethyl ethanoate, which belongs to a class of compounds called esters, and water is also produced.

This type of reaction involves combining an alcohol and a carboxylic acid to form an ester and water.

The specific name given to this reaction is esterification.

Therefore, the reaction shown is an esterification reaction.

Boiling point depends on the strength of intermolecular forces between molecules. Stronger intermolecular forces require more energy to separate the molecules, resulting in a higher boiling point.

Alcohols such as ethanol and propanol can form hydrogen bonds, which are stronger than the forces present in substances like hexane and chloropropane.

Between ethanol and propanol, propanol has a longer carbon chain, which increases the surface area and strengthens the intermolecular attractions even further.

Because propanol has both hydrogen bonding and a longer molecular structure, it has the strongest intermolecular forces among the options.

Therefore, propanol has the highest boiling point.

The feasibility of a reaction depends on the Gibbs free energy change, which is given by the relation

\[ \Delta G = \Delta H - T\Delta S \]

For a reaction to occur spontaneously, the value of \( \Delta G \) must be negative.

If both enthalpy change \( \Delta H \) and entropy change \( \Delta S \) are positive, then the term \( -T\Delta S \) becomes negative.

As temperature increases, this negative term becomes larger in magnitude and can make the overall value of \( \Delta G \) negative.

This means the reaction becomes feasible under such conditions.

Therefore, the condition where both \( \Delta H \) and \( \Delta S \) are positive can allow the reaction to be feasible.

Potassium trioxochlorate(V) is a strong oxidizing agent. During the preparation of oxygen, if it comes into contact with materials such as dust, grease, or other carbon-containing substances, a highly reactive mixture can form.

This mixture can react violently because the oxidizing agent promotes rapid oxidation of these materials.

Such reactions may occur suddenly and can cause explosions, making the process unsafe.

Because of this risk of forming explosive mixtures, this method is no longer preferred in modern laboratories.

Ammoniacal copper(I) chloride solution is used to selectively remove certain gases by forming chemical complexes with them.

Carbon monoxide has the ability to combine with copper(I) ions present in the solution to form a stable coordination compound.

This interaction allows carbon monoxide to dissolve in the solution and be removed from the gas mixture.

Other gases such as hydrogen and nitrogen do not form such complexes and therefore remain unabsorbed.

Hence, the gas absorbed by ammoniacal CuCl\(_2\) solution is carbon monoxide.