In an experiment to measure the heat of reaction for the reaction between sodium hydroxide with hydrochloric acid, a student added 50 cm³ of 1.0 M HCl solution to the same volume of 1.0 M NaOH solution in a polystyrene foam cup - Leaving Cert Chemistry - Question 3 - 2007

The burette should have been used, as it provides more precise measurements compared to a graduated cylinder, minimizing measurement errors.

To obtain the initial temperature, both solutions should be allowed to equilibrate at the same room temperature before mixing. Measure the temperature of each solution separately with a thermometer and record the average of these temperatures. This ensures an accurate representation of the starting temperature of the reaction.

1. Use a thermometer with a sensitivity of 0.2 °C to ensure accurate temperature readings.
2. Measure quickly and minimize heat loss by covering the reaction mixture.
3. Stir the mixture gently but thoroughly to ensure uniform temperature distribution and prevent localized temperature anomalies.

The polystyrene foam cup acts as a better insulator, minimizing heat loss during the reaction. This ensures that the temperature rise measurement is more accurate compared to using a glass beaker, which can conduct heat away from the reaction mixture.

To find the number of moles of acid neutralised:

Given that 50 cm³ of 1.0 M HCl was used, the number of moles is 0.05 mol.

Using the heat capacity formula:

Substituting the values:

$ext{Heat} = 0.05 ext{ mol} imes 420 ext{ J K}^{-1} imes 6.7 ext{ °C} = 14.07 ext{ kJ}$

The apparatus used is called a 'bomb calorimeter'. It is specifically designed for measuring the heat of combustion reactions.