2025 - JAMB Chemistry Past Questions and Answers - page 6

The oxidation state of nitrogen can be calculated by using the rule that oxygen has an oxidation state of −2 and the total oxidation state of all atoms in a neutral compound is zero. For N₂O₃, let the oxidation state of nitrogen be x. The total oxidation state of nitrogen is 2x, and oxygen contributes 3 × (−2) = −6. Since the compound is neutral, the sum must equal zero, so 2x − 6 = 0. Solving this gives 2x = 6, so x = +3.

Therefore, nitrogen has an oxidation state of +3 in N₂O₃.

The valence electrons are found in the outermost energy level, which is the third shell in this configuration. The electrons in the outer shell are in 3s² and 3p⁵. Adding these gives 2 + 5 = 7 valence electrons. Elements are placed in groups according to the number of valence electrons. An element with 7 valence electrons belongs to Group 7.

Therefore, the element belongs to Group 7.

A physical change is one in which the substance does not form a new chemical substance and can often be reversed by physical means. When sodium chloride dissolves in water, the salt separates into ions and mixes with water, but no new substance is formed. The salt can be recovered by evaporating the water. Since the original substances remain chemically unchanged, this process is a physical change.

Therefore, dissolving sodium chloride in water is the correct answer.

A suspension is a mixture in which solid particles are dispersed in a fluid but do not dissolve. These particles are large enough to settle out over time. Dust and sand particles in air remain suspended temporarily but eventually settle due to gravity. Since the particles are not dissolved and the mixture is not uniform, it is classified as a suspension.

Therefore, the correct answer is a suspension.

Carbon(II) oxide, also called carbon monoxide, is formed when carbon-containing fuels burn with insufficient oxygen. In complete combustion, carbon reacts fully with oxygen to form carbon dioxide, but when oxygen is limited, carbon monoxide is produced instead. This commonly happens in engines and poorly ventilated combustion systems.

Therefore, combustion of fuel is the source of carbon(II) oxide.

KOH is a strong base and dissociates completely in water to produce hydroxide ions, so the hydroxide ion concentration is [OH⁻] = 0.001 M. The pOH is calculated using the formula pOH = −log[OH⁻]. Substituting the value gives pOH = −log(0.001). Since 0.001 = 10⁻³, this gives pOH = 3. The relationship between pH and pOH is pH + pOH = 14. Substituting the value of pOH gives pH + 3 = 14. Solving gives pH = 11.

Therefore, the pH of the solution is 11.

In the blast furnace, iron ore is reduced using coke and limestone at high temperature. The molten iron produced contains a high percentage of carbon and impurities. This impure iron collected directly from the furnace is known as pig iron. Further processing is required to convert it into other forms such as steel or wrought iron.

Therefore, the iron obtained directly from the blast furnace is pig iron.

Acid radicals are negatively charged ions formed when acids lose hydrogen ions. These ions are called anions. Examples include carbonate (CO₃²⁻), sulfate (SO₄²⁻), and nitrate (NO₃⁻). These all carry negative charges. Any species with a positive charge, such as Na⁺, K⁺, or Mg²⁺, is a cation and not an acid radical.

Therefore, the correct answer is the group containing CO₃²⁻, SO₄²⁻, and NO₃⁻.

Fructose has the molecular formula C₆H₁₂O₆. The general formula of carbohydrates is written as Cₓ(H₂O)ᵧ. Comparing this with the molecular formula of fructose, there are 6 carbon atoms present.

Therefore, the value of x, which represents the number of carbon atoms, is 6.

When copper ions are reduced, the reaction is Cu\(^{2+}\) + 2e\(^-\) → Cu. This shows that 2 moles of electrons are needed to deposit 1 mole of copper.

One mole of electrons carries 96500 C of charge, so 2 moles of electrons carry 2 × 96500 = 193000 C. This amount of charge deposits 1 mole of copper, which has a mass of 64 g.

This means 193000 C deposits 64 g of copper. To find the charge required for 4.5 g, proportional reasoning is used:

\[ Q = \frac{193000 \times 4.5}{64} \]

\[ Q = \frac{868500}{64} \]

\[ Q = 13570.3125 \text{ C} \]

Since current is defined as charge divided by time, the relationship is:

\[ I = \frac{Q}{t} \]

Rearranging for time gives:

\[ t = \frac{Q}{I} \]

\[ t = \frac{13570.3125}{2.5} \]

\[ t = 5428.125 \text{ seconds} \]

Therefore, the time required is approximately 5428 seconds.