2025 - JAMB Chemistry Past Questions and Answers - page 4

Reduction involves the gain of electrons, which corresponds to a decrease in oxidation state.

In the reaction, sodium initially exists as neutral atoms with oxidation state 0, and chlorine also exists as Cl\(_2\) with oxidation state 0.

After the reaction, sodium becomes Na\(^+\), meaning it has lost electrons and is oxidized.

Chlorine becomes Cl\(^-\), meaning it has gained electrons. This change in oxidation state from 0 to −1 shows that chlorine has gained electrons.

Therefore, chlorine gas (Cl\(_2\)) is the species that undergoes reduction.

Permalloy is a special type of alloy formed by combining iron with another metal to improve its magnetic properties.

The element added in large proportion is nickel.

The presence of nickel enhances the magnetic behavior of the alloy, making it highly useful in devices such as transformers and magnetic shields.

Therefore, permalloy consists mainly of iron and nickel.

Ammonium trioxonitrate(V), which is written chemically as NH\(_4\)NO\(_3\), breaks down when heated.

This decomposition produces nitrous oxide gas and water vapor.

The balanced chemical equation for this reaction is

\[ \text{NH}_4\text{NO}_3 \rightarrow \text{N}_2\text{O} + 2\text{H}_2\text{O} \]

This shows that the products formed are dinitrogen monoxide and water.

Therefore, the products are N\(_2\)O and H\(_2\)O.

Boiling point depends on how strongly molecules attract each other. Stronger intermolecular forces require more heat energy to separate the molecules.

Alkanoic acids contain the carboxyl group (–COOH), which allows two molecules to form multiple hydrogen bonds with each other.

This leads to very strong attraction between molecules, often forming stable paired structures.

In comparison, alkanols can form hydrogen bonds but not as extensively as alkanoic acids.

Because of these stronger hydrogen bonds, alkanoic acids require more energy to boil, resulting in higher boiling points.

A polar covalent bond occurs when two atoms share electrons unequally.

This happens because one atom attracts the bonding electrons more strongly than the other due to higher electronegativity.

As a result, the shared electron pair spends more time closer to one atom, creating partial positive and partial negative charges.

This unequal distribution of the bonding electrons is the defining feature of a polar covalent bond.

Therefore, it involves unequal sharing of the electron pair.

Atoms in solids are not completely stationary; they can move slowly over time.

When two different metals are in close contact, atoms from one metal gradually move into the other metal.

This movement occurs from regions of higher concentration to regions of lower concentration until they become more evenly distributed.

This gradual movement of particles in solids is called diffusion.

Therefore, gold atoms are found in silver due to diffusion.

Catalysts increase the rate of reactions by providing alternative pathways for reactions to occur.

Transition metals are especially effective catalysts because their d-orbitals are not completely filled.

These partially filled d-orbitals allow them to form temporary bonds with reacting substances.

This ability helps weaken existing bonds in reactants and makes it easier for new products to form.

Therefore, the presence of partially filled d-orbitals makes metals suitable as catalysts.

The given compound contains the functional group –COO–, which indicates that it is an ester.

Esters are formed by the reaction between a carboxylic acid and an alcohol.

The portion CH\(_3\)CH\(_2\)COO– comes from propanoic acid, since replacing the ester linkage with –COOH gives CH\(_3\)CH\(_2\)COOH.

The portion –CH\(_2\)CH\(_3\) comes from ethanol, since replacing the ester linkage with –OH gives CH\(_3\)CH\(_2\)OH.

Therefore, the ester was formed from propanoic acid and ethanol.

Each of the substances used removes specific components of air.

Alkaline pyrogallol absorbs oxygen from the air.

Potash removes carbon dioxide by reacting with it.

Fused calcium chloride absorbs water vapor because it acts as a drying agent.

After removing oxygen, carbon dioxide, and water vapor, the remaining gases are nitrogen and the noble gases, since they do not react with these absorbents.

Therefore, the gases left unabsorbed are noble gases and nitrogen.

Litmus paper is used to distinguish between acidic, neutral, and basic solutions. A solution with pH less than 7 is acidic, a solution with pH equal to 7 is neutral, and a solution with pH greater than 7 is basic. Red litmus paper changes to blue only when it is placed in a basic solution. Looking at the given values, 2.5 and 3.5 are both less than 7, so they represent acidic solutions and will not turn red litmus blue. A pH of 7.0 is neutral and produces no change in litmus color. The pH value of 8.0 is greater than 7, meaning the solution is basic, and bases turn red litmus paper blue.

Therefore, the correct answer is 8.0.