Chemistry 2018 Jamb Examination

Given: V = 10.0 dm³, P = 4 atm, T = 273 + 273 = 546 K At standard temperature and pressure (s.t.p), 1 mol of gas occupies 22.4 dm³ at 1 atm and 273 K.
Using the combined gas law:\[ \dfrac{P_1 V_1}{T_1} = \dfrac{P_2 V_2}{T_2} \]Substituting to find the equivalent volume at s.t.p:\[ V_2 = \dfrac{P_1 V_1 T_2}{P_2 T_1} \]\[= \dfrac{4 \times 10.0 \times 273}{1 \times 546} = 20.0 \; \text{dm}^3 \]Since 22.4 dm³ corresponds to 1 mole, the number of moles is:\[ n = \dfrac{20.0}{22.4} = 0.89 \; \text{mol} \]Therefore, the number of moles of gas present is 0.89 mol.

Charles' law states that the volume of a given mass of gas is directly proportional to its absolute temperature, provided pressure remains constant.
Extrapolating the graph of volume against temperature shows that the volume becomes zero at -273°C, known as absolute zero or 0 K.
At this temperature, the motion of gas particles theoretically stops.

Ethene (C₂H₄) acts as a natural plant hormone that promotes fruit ripening. It triggers the enzymatic processes responsible for softening, colour change, and conversion of starch to sugar in fruits.
Propane, methane, and butane are alkanes and do not possess this property.

Copper(II) sulphide (CuS) is insoluble in dilute acids like HCl because it has a very low solubility product constant (Ksp).
In contrast, FeS, ZnS, and Na₂S react with dilute acids to produce hydrogen sulphide gas (H₂S).
Therefore, CuS remains undissolved in dilute hydrochloric acid.

Sodium hydroxide is a strong base and dissociates completely in water:\[ \text{NaOH} \rightarrow \text{Na}^+ + \text{OH}^- \]Therefore, \([\text{OH}^-] = 0.001 \; \text{mol dm}^{-3}\).
pOH = -log(0.001) = 3.
Since pH + pOH = 14,\[ \text{pH} = 14 - 3 = 11 \]Thus, the pH of the solution is 11.

In the complex ion [Cu(NH₃)₄]²⁺, the four ammonia molecules each donate a lone pair of electrons to the central copper ion (Cu²⁺).
This type of bond, where both electrons come from the same atom, is known as a coordinate or dative covalent bond.
Hence, the bonding in the complex is coordinate.

Rusting of iron involves a chemical reaction between iron, oxygen, and water vapour, forming hydrated iron(III) oxide (rust).
This process results in the formation of a new substance with different properties, indicating a chemical change.
The other options involve physical changes.

Using the ideal gas law: \( PV = nRT \).
If both pressure and volume are doubled, the temperature must increase by a factor of four:\[ P_2 V_2 = 4 P_1 V_1 = nR T_2 \]\[ \Rightarrow T_2 = 4 T_1 \]\[ \Rightarrow T_2 = 4 \times 273 = 1092 \; \text{K} \]Thus, the gas must be heated to 1092 K.

The kinetic theory of gases states that the average kinetic energy of gas molecules is directly proportional to the absolute temperature (in kelvin).
When temperature increases, the speed and energy of gas molecules increase accordingly.
Hence, the kinetic energy increases with temperature.

Sulphur is a key component in the production of matches. It serves as a combustible material that ignites when rubbed against a rough surface, helping to sustain the flame.
Nitrogen, aluminium, and copper do not play this role in match production.