Question

1. Which acid listed will produce the lowest [H₃O⁺] in a 0.30 M solution? Hydroiodic acid, sulfuric acid, acetic acid, nitrous acid, hydrocyanic acid, hydrosulfuric acid, chlorous acid.

a. Explain your reasoning without dong any calculations

b. Confirm your reasoning by performing calculations

Answer 1

1)

a) answer : hydrocyanic acid

strong acids have high [H3O+] , weak acids have low [H3O+].

here in the given list ,

HI is the strong acid among all. so it has high [H3O+] , HCN is weak acid , so it has low [H3O+]

b)

Hydroiodic acid - HI   ----------> strong acid

sulfuric acid -- H2SO4 ----------> strong acid

acetic acid - CH3COOH   ---------> weak acid , Ka = 1.8 x 10^-5

nitrous acid - HNO2   ---------> weak acid , Ka = 5.6 x 10^-4

,hydrocyanic acid - HCN ---------> weak acid , Ka = 6.2×10^–10

hydrosulfuric acid = H2S   ---------> weak acid , Ka = 8.9×10^–8

chlorous acid.= HClO2   ------------> weak acid , Ka = 1.1 x 10^-2

[H3O+] = sqrt (Ka x C)

here Ka valuelow , then [H3O+] is low

HCN has lowest Ka values. so it has low [H3O+]

[H3O+] = sqrt (Ka x C)

            = sqrt (6.2×10^–10 x 0.30)

           = 1.36 x 10^-5 M