A student carried out an experiment to find the temperature rise for a reaction between hydrochloric acid and sodium hydroxide solution - AQA - A-Level Chemistry - Question 4 - 2018 - Paper 3

The temperature rise, ΔT, can be calculated from the graph. If ΔT = 21.4 °C - 19.8 °C = 1.6 °C, then the percentage uncertainty can be calculated as:

ext{Percentage Uncertainty} = rac{0.1}{ ext{Value}} imes 100 = rac{0.1}{1.6} imes 100 = 6.25 \%

Replace the glass beaker with a polystyrene cup to insulate the glass better, which will help retain the heat generated during the reaction.

Increase the magnitude of temperature change by using more concentrated acid or base solutions. A larger temperature rise can lead to a clearer distinction in readings, thus reducing the percentage uncertainty associated with each measurement.

The balanced equation for the reaction is:

$\text{HOOC-COOH} + 2 \text{KOH} \rightarrow \text{K}_2\text{HOOC-COO} + 2 \text{H}_2\text{O}$

To calculate the enthalpy change (ΔH): First, calculate the heat absorbed using the formula:

$q = m \cdot c \cdot \Delta T$

Where:

• m = mass (g) = volume (cm³) × density (g/cm³)
• c = specific heat capacity = 4.2 J/g°C
• ΔT = temperature change = 3.2°C

Substituting, we find: $m = (25 + 75) \cdot 1.00 = 100 \text{ g}$ $q = 100 \cdot 4.2 \cdot 3.2 = 1344 \text{ J}$

To find ΔH per mole of water formed:

• Moles of water = 0.050 moles
• Therefore:

The differences may arise due to variations in the strength of the acids and bases used. Sulfuric acid is a strong acid that fully dissociates, leading to a more exothermic reaction, whereas ethanedioic acid is a weaker acid that does not completely dissociate. Consequently, reactions involving stronger acids generally release more heat as compared to the reactions involving weaker acids, affecting the calculated enthalpy change.