2024 - JAMB Chemistry Past Questions and Answers - page 3

Here's how to solve this problem:

1. Write the balanced chemical equation for the combustion of ethanol:
   C₂H₅OH + 3O₂ → 2CO₂ + 3H₂O
2. Calculate the number of moles of oxygen (O₂) used:
   Molar mass of O₂ = 2 × 16 g/mol = 32 g/mol
   Moles of O₂ = mass / molar mass = 6 g / 32 g/mol = 0.1875 mol
3. Determine the mole ratio between O₂ and CO₂ from the balanced equation:
   3 moles of O₂ produce 2 moles of CO₂
4. Calculate the moles of CO₂ produced:
   Moles of CO₂ = 0.1875 × (2/3) = 0.125 mol

Therefore, the moles of CO₂ produced is 0.125 mol.

The dissociation of Na₂X into Na⁺ and X^2- indicates the formation of ions. Therefore, the bond is:

• Ionic bonds: Formed by transfer of electrons and electrostatic attraction between ions.
• Covalent bonds: Involve sharing of electrons.
• Dative bonds: A type of covalent bond where both electrons come from the same atom.
• Metallic bonds: Characteristic of metals with delocalized electrons.

Since ions are formed, the bond between Na and X is most likely ionic.

Oil pollution in coastal waters primarily destroys aquatic life:

• Destruction of aquatic life: Oil can suffocate marine organisms, coat birds' feathers, and contaminate the food chain.
• Nitrification of water: Indirectly affected, not a major effect.
• Detoxification: Oil introduces toxicity rather than detoxifying water.
• Disinfection: Oil pollution does not disinfect water.

The graph illustrates energy changes during a chemical reaction. The y-axis represents energy, showing the energy barrier reactants must overcome to form products, known as the activation energy.

According to Le Chatelier's Principle, if pressure is increased, equilibrium shifts to reduce stress. Only gas moles affect this shift. Both sides have 1 mole of gas, so increasing pressure has no effect.

This configuration follows Hund's rule: electrons occupy each orbital singly before pairing. All three p orbitals are singly occupied, making this the most stable ground state for Nitrogen.

The incorrect formula is Iron(III) bromide:

1. Identify the ions: Fe³⁺ and Br⁻.
2. Balance the charges: Three Br⁻ ions balance one Fe³⁺ ion.
3. Correct formula: FeBr₃.

1. Calculate molar mass:
   5.6 dm³ has mass 11.0 g.
   1 mole = 22.4 dm³.
   Molar mass = (11.0 / 5.6) × 22.4 = 44 g/mol.
2. Vapour density = Molar mass / 2 = 44 / 2 = 22.

The suitable method is fractional distillation of liquid air:

• Air is cooled and compressed to liquid.
• Gases vaporize at different boiling points; nitrogen vaporizes first.
• Catalytic cracking, thermal decomposition, and catalytic decomposition are unsuitable as they change chemical composition.

With limited air, incomplete combustion occurs:

• Not all carbon converts to CO₂.
• Some carbon forms CO and soot.
• Water is also produced.

Correct answer: soot and CO.