A chemist prepares 0.10 M aqueous solutions of each of the following acids - VCE - SSCE Chemistry - Question 9 - 2010 - Paper 1

To determine which of the given acids produces the lowest pH, we need to evaluate their strengths based on their dissociation in water.

1. Comparing Acid Strengths:

   • CH₃COOH (Acetic Acid): A weak acid with a dissociation constant (Ka) of approximately 1.8 x 10^-5.
   • HNO₂ (Nitrous Acid): A weak acid but stronger than acetic acid, with a Ka of about 4.5 x 10^-4.
   • HCN (Hydrocyanic Acid): A weak acid with a Ka of around 6.2 x 10^-10, making it a very weak acid.
   • HOCl (Hypochlorous Acid): A weak acid with a Ka of about 3.5 x 10^-8, stronger than HCN but weaker than HNO₂ and CH₃COOH.

2. Lowest pH Out of the Listed Acids:

   • Since HNO₂ is stronger than both CH₃COOH and HOCl, it will produce more H⁺ ions in solution, leading to a lower pH.
   • HCN, being the weakest of all, will contribute the least to the acidity.

3. Conclusion: Therefore, among the given options, the solution of HNO₂ will have the lowest pH.