The cardboard cup with plastic lid in the diagram contained 150 cm³ of 1.0 M hydrochloric acid solution at room temperature - Leaving Cert Chemistry - Question 3 - 2018

The mixture should be stirred to ensure that the temperature is uniform throughout the solution. This helps to avoid measuring a local hot or cold spot and gives a more accurate overall temperature.

The temperature began to fall gradually due to heat loss to the surroundings. As the reaction continues to occur and the system loses heat to the environment, the overall temperature of the mixture decreases.

If the thermometer had been accurate to 1 K, larger fluctuations in temperature would likely have been recorded, potentially reflecting the maximum temperature reached by the reaction instead of the smaller changes that a more precise thermometer would detect.

Moderately concentrated solutions are advantageous because they react more quickly, leading to a more significant temperature change. Dilute solutions may result in slower reaction rates and less thermal change, making it harder to measure the heat of reaction accurately.

The hazard pictogram for 1.0 M NaOH should display a corrosion symbol, indicating that it can cause skin and eye irritation. It is typically represented as a hand and face being corroded by a chemical, and it warns of the potential harm this substance can cause.

To calculate the moles of HCl, use the concentration and volume:

$n = C imes V$ Where:

• C = concentration (1.0 M),
• V = volume (150 cm³ or 0.150 L). Thus:

$n = 1.0 imes 0.150 = 0.150 ext{ mol}$

Therefore, 0.150 moles of HCl were neutralised.

Using the formula for heat absorbed:

$q = m imes c imes riangle T$ Where:

• m = mass (310 g),
• c = specific heat capacity (4.2 kJ kg⁻¹ K⁻¹),
• $riangle T = 6.4 K$. Therefore:

$q = 0.310 imes 4.2 imes 6.4 = 8.3 ext{ kJ}$.

To find ΔH per mole:

ΔH = rac{q}{ ext{moles of HCl}} = rac{8.3 ext{ kJ}}{0.150 ext{ mol}} = 55.6 ext{ kJ mol}^{-1}.

A possible modification is to use an insulated calorimeter to minimize heat loss to the surroundings. By ensuring that heat does not escape the system, the temperature change can be measured more accurately, leading to a better calculation of ΔH.