Equal volumes of two solutions, each with the same concentration, are mixed together at 298 K - AQA - A-Level Chemistry - Question 15 - 2022 - Paper 3

To determine which solution will yield a pH greater than 7 upon mixing, we need to analyze the properties of the given pairs.

1. HCOOH and HCOOK:

   • HCOOH (formic acid) is a weak acid and HCOOK (potassium formate) is its salt. Mixing them will produce a neutral solution.

2. KOH and CH3COOH:

   • KOH is a strong base, while CH3COOH (acetic acid) is a weak acid. The reaction between them will result in the formation of water and acetate ions, which leads to a basic solution. This combination will definitely yield a pH > 7.

3. NH3 and HCl:

   • NH3 (ammonia) is a weak base, while HCl is a strong acid. Their reaction forms NH4Cl, which will result in a solution with a pH < 7.

4. NH4Cl and KCl:

   • NH4Cl is the salt of a weak base (NH3) and a strong acid (HCl), resulting in a solution that is slightly acidic (pH < 7). KCl is neutral.

Therefore, the only pair that results in a solution with a pH > 7 is KOH and CH3COOH.