This question is about hydrogen chloride and hydrochloric acid - AQA - GCSE Chemistry Combined Science - Question 6 - 2022 - Paper 1

A strong acid is one that completely ionizes or dissociates in aqueous solution, resulting in a high concentration of hydronium ions (H₃O⁺) in the solution. This allows strong acids to effectively lower the pH of the solution.

Magnesium can be used to distinguish between strong and weak acids by observing its reactivity. Magnesium reacts more vigorously with strong acids, resulting in rapid fizzing and the quicker disappearance of the magnesium metal. In contrast, the reaction with a weak acid will be slower and less vigorous.

When the concentration of hydrochloric acid is increased by a factor of 100, the pH decreases by 2. This is calculated using the formula:

$ext{Change in pH} = - ext{log}_{10}( ext{factor})$

For a factor of 100, the change in pH is:

$ext{Change in pH} = - ext{log}_{10}(100) = -2$.

To calculate bond energy X, we need to apply the given bond energies to determine the energy involved in the reaction:

1. Calculate the total energy of bonds broken:

   • Bonds broken: (4 x 413 kJ/mol) + (C=C bond) = 1652 + x

2. Calculate the total energy of bonds formed:

   • Bonds formed: (5 x 413) + (C-C) + (C-Cl) = 2065 + 346 + 339 = 2750 kJ/mol

3. The energy released is 56 kJ/mol greater than the energy required to break the existing bonds:

   • Energy released = Energy broken - Energy formed
   • (1652 + x) - 2750 = -56
   • Solving the above gives: $x = 611 ext{ kJ/mol}$.