Question

Consider the following mathematical expressions.

a. [H⁺] = [HA]₀

b. [H⁺] = (Ka × [HA]₀)^1/2

c. [OH^-] = 2[B]₀

d. [OH^-] = (Kb × [B]₀)^1/2

For each expression, give three solutions where the mathematical expression would give a good approximation for the [H⁺] or [OH^-]. [HA]₀ and [B]₀ represent initial concentrations of an acid or a base.

Short answer

1. HCl, HNO₃ and HClO₄
2. HCN, HF and CH₃COOH
3. Ca(OH)₂, Ba(OH)₂ and Sr(OH)₂
4. NH₄OH, NH₃ and CH₃NH₂

Step-by-step solution

Describing a

As strong acid dissociates completely so for strong acids

[H⁺] = [HA]₀

Examples: HCl, HNO₃ and HClO₄

Describing b

For weak acids [H⁺],

[H⁺] =(Ka× [HA]₀)^1/2

Examples: HCN, HF and CH₃COOH

Describing c

As strong base dissociates completely so for strong base

[OH^-] = [B]₀

But for diacidic base

[OH^-] = 2[B]₀

Examples: Ca(OH)₂, Ba(OH)₂ and Sr(OH)₂

Describing d  

For weak bases [OH^-],

[OH^-] =(K_b× [B]₀)^1/2

Examples: NH₄OH, NH₃ and CH₃NH₂