In: Chemistry
Which of the following solutions would have the highest pH? Assume that they are all 0.10 M in acid at 25C. The acid is followed by its Ka value.
1) HF, 3.5 × 10-4
2) HCHO2, 1.8 × 10-4
3) HNO2, 4.6 × 10-4
4) HCN, 4.9 × 10-10
5) HClO2, 1.1 × 10-2
Answer: 4) HCN, 4.9 × 10-10
Explanation:
Ka, the acid ionization constant, is the equilibrium constant for chemical reactions involving weak acids in aqueous solution. The numerical value of Ka is used to predict the extent of acid dissociation. A large Ka value indicates a stronger acid (more of the acid dissociates) and small Ka value indicates a weaker acid (less of the acid dissociates).
As HCN has lowest Ka value, it indicates a weaker
acid (less of the acid dissociates). Thus HCN solutions has highest
pH than other solutions because less acid dissociates into the
solution compared to other chemical solutions which has high
Ka values.