When 50cm³ of 2M HCl was neutralised by an equal volume of 2M NaOH, it initially rose to a minimum of 33.7°C. What is the molar enthalpy of neutralisation of NaOH?

The total volume of the solution is $50 \text{ cm}^3 + 50 \text{ cm}^3 = 100 \text{ cm}^3$.
Assuming the density of the solution is $1 \text{ g/cm}^3$, the mass of the solution is $100 \text{ g}$.
The change in temperature is $\Delta T = 33.7 \text{ °C} - 20 \text{ °C} = 13.7 \text{ °C}$.
The specific heat capacity is $4.2 \text{ kJ kg}^{-1} \text{ K}^{-1}$, which is equivalent to $4.2 \text{ J g}^{-1} \text{ K}^{-1}$.

Moles of HCl = Concentration $\times$ Volume (in dm³)
Moles of HCl = $2 \text{ M} \times (50/1000) \text{ dm}^3 = 2 \text{ M} \times 0.050 \text{ dm}^3 = 0.10 \text{ mol}$
The neutralization reaction is $HCl(aq) + NaOH(aq) \longrightarrow NaCl(aq) + H_2O(l)$. The mole ratio is 1:1, so $0.10 \text{ mol}$ of neutralization occurred.

The heat released is $Q = 5.754 \text{ kJ}$. Since the temperature increased, the reaction is exothermic, so the enthalpy change is negative.

The molar enthalpy of neutralization of NaOH is $\boxed{\mathbf{-57.54 \text{ kJ mol}^{-1}}}$.

2) Draw and name two positional isomers of alkanol C₄H₉OH.

Positional isomers have the same molecular formula and carbon skeleton but differ in the position of the functional group.

• Isomer 1: The hydroxyl group (-OH) is on the first carbon atom.

  $$\text{CH}_3\text{CH}_2\text{CH}_2\text{CH}_2\text{OH}$$

  Name: Butan-1-ol

• Isomer 2: The hydroxyl group (-OH) is on the second carbon atom.

  $$\text{CH}_3\text{CH}_2\text{CH(OH)}\text{CH}_3$$

  Name: Butan-2-ol

3) Explain why metals such as Mg and Al are good conductors of electricity.

Metals like magnesium and aluminum are good conductors of electricity because they contain delocalized electrons. These valence electrons are not fixed to individual atoms but are free to move throughout the entire metallic structure. When an electric potential difference is applied, these mobile electrons can easily flow, carrying electric charge and thus conducting electricity.

4) Give a reason why Al is preferred to Mg for making cooking pans.

Aluminum is preferred over magnesium for making cooking pans primarily due to its superior corrosion resistance. Aluminum forms a thin, tough, and impermeable layer of aluminum oxide (Al₂O₃) on its surface when exposed to air, which protects the underlying metal from further corrosion, especially from acids found in food. Magnesium is more reactive and can corrode more easily, particularly in the presence of water or acids at cooking temperatures.