2025 - JAMB Chemistry Past Questions and Answers - page 2

A diagonal relationship occurs between certain elements in the periodic table that are positioned diagonally to each other across Period 2 and Period 3.

These elements have similar ionic sizes and charge densities, which makes their chemical properties similar.

Examples of such pairs include lithium and magnesium, beryllium and aluminium, and boron and silicon.

Among the options given, boron and silicon form one of these diagonal pairs.

Therefore, the correct pair is boron and silicon.

An acid used in baking and soft drinks must be safe for consumption and capable of producing carbon dioxide when reacting with sodium bicarbonate.

Tartaric acid reacts with baking soda to produce carbon dioxide gas, which helps baked products rise.

It is also commonly used in beverages to provide acidity and improve taste.

Since it performs both functions effectively, tartaric acid is the correct substance used in these applications.

Therefore, the acid used is tartaric acid.

Glucose can be broken down by enzymes present in microorganisms such as yeast.

During this process, glucose molecules are converted into ethanol and carbon dioxide.

The chemical equation representing this process is:
\[C_6H_{12}O_6 \rightarrow 2C_2H_5OH + 2CO_2\]

This type of chemical change occurs without oxygen and is brought about by enzymes.

This process is called fermentation.

Therefore, the enzymatic conversion of glucose to ethanol is fermentation.

To determine the name, the longest continuous carbon chain containing the hydroxyl group must first be identified. Counting through the structure shows that the longest chain contains six carbon atoms, so the parent name is hexane.

The hydroxyl group is attached to the third carbon when numbering is done from the end closest to the hydroxyl group. This makes the base name hexan-3-ol.

Next, the positions of the methyl substituents are identified. One methyl group is attached to carbon 2, and two methyl groups are attached to carbon 5.

Since there are three methyl groups in total, the prefix trimethyl is used, and their positions are written as 2,5,5.

Combining all parts gives the name 2,5,5-trimethylhexan-3-ol.

Dead plants and animals contain nitrogen in complex organic forms such as proteins.

Microorganisms in the soil break down these organic nitrogen compounds into simpler substances.

The first inorganic nitrogen compound formed during this decomposition process is ammonia.

This process is an important part of the nitrogen cycle and prepares nitrogen for further conversion into other forms usable by plants.

Therefore, nitrogenous compounds in dead matter are converted into ammonia.

A neutral solution has equal concentrations of hydrogen ions and hydroxide ions.

This happens when a salt is formed from a strong acid and a strong base.

Sodium chloride is formed from hydrochloric acid, which is a strong acid, and sodium hydroxide, which is a strong base.

When sodium chloride dissolves in water, it does not affect the balance of hydrogen and hydroxide ions.

As a result, the solution remains neutral with a pH of 7.

Therefore, sodium chloride produces a neutral solution.

Blowing agents are substances used to create gas bubbles within materials.

These bubbles expand and form a foam structure, making the material light and useful for insulation and packaging.

Chlorofluorocarbons were widely used for this purpose because they easily form gases and help produce foam materials.

Therefore, their use as blowing agents is mainly in the foam industry.

A colloid consists of one substance dispersed in another substance.

In spray deodorants, very small liquid droplets are dispersed in a gas.

This type of colloidal system, where liquid particles are spread in a gas medium, is called an aerosol.

Therefore, commercial deodorant is an example of an aerosol.

Sodium metal can be obtained from molten sodium chloride using electricity.

In this process, sodium ions gain electrons at the cathode to form sodium metal, while chloride ions lose electrons at the anode to form chlorine gas.

This industrial electrolytic method is specifically known as the Downs process.

Therefore, sodium is produced by the Downs process.

When pressure is increased in a system involving gases, the system adjusts to reduce the pressure by favoring the side with fewer gaseous particles.

On the left side of the equation, there are two gaseous reactant molecules, NH\(_3\) and HCl. On the right side, ammonium chloride is formed, which represents fewer gaseous particles compared to the reactants.

Since the product side has fewer gas molecules, increasing the pressure shifts the equilibrium toward the product side. This shift helps reduce the total pressure by decreasing the number of gas particles present.

Therefore, increasing the pressure promotes the formation of NH\(_4\)Cl, meaning the products are favored.