Chemistry 2008 Jamb Examination

Insoluble salts are prepared by double decomposition or precipitation method. This involves mixing solutions of two soluble salts such that an insoluble salt is formed as a precipitate.

Let the oxidation state of carbon be x. In HCOOH:  
x + (1 × 1) + (1 × -2) + (1 × -2) + (1 × 1) = 0  
x + 1 - 2 - 2 + 1 = 0  
x - 2 = 0  
x = +2

NaClO contains chlorine in the +1 oxidation state. The correct IUPAC name is sodium oxochlorate (I).

During recharging, oxidation occurs at the anode and reduction at the cathode. At the cathode, lead(II) ions are reduced to lead metal: \[ Pb^{2+}(aq) + 2e^- \; \rightarrow \; Pb(s) \]

For Zn: molar mass = 65 g, valency = 2, equivalent mass = \( \dfrac{65}{2} = 32.5 \). For Hg: molar mass = 201 g, valency = 2, equivalent mass = \( \dfrac{201}{2} = 100.5 \). Using Faraday’s law: \[ \dfrac{\text{Mass of Zn}}{\text{Eq. mass of Zn}} = \dfrac{\text{Mass of Hg}}{\text{Eq. mass of Hg}} \] \[ \dfrac{0.65}{32.5} = \dfrac{m}{100.5} \] \[ m = \dfrac{0.65 \times 100.5}{32.5} = 2.01 \; g \]

Two moles of gaseous reactants form one mole of solid product. This results in decreased randomness, so entropy change is negative.

The reaction  C(s) + H₂O(g) → CO(g) + H₂(g) requires heat to proceed, hence it is endothermic.

Catalysts provide an alternative reaction pathway with lower activation energy, thereby increasing the rate of reaction.

Lower concentration reduces the frequency of collisions between reactant particles, leading to a slower reaction rate.

Oxygen is used to oxidize and remove impurities such as carbon, sulphur, and phosphorus from pig iron in steelmaking.