Question

If the concentrations of two weak acids are different and degrees of ionisation $\left(\alpha \right)$ are very less, then their relative strengths can be compared by:

• A. $\frac{{\left[H^{+}\right]}_1}{{\left[H^{+}\right]}_2}$
• B. $\frac{{\alpha }_1}{{\alpha }_2}$
• C. $\frac{C_1{\alpha }_1^2}{C_2{\alpha }_2^2}$
• D. $\frac{K_{a1}{C}_1}{K_{a2}{C}_2}$

Answer 1

Answer: (A), (C)

The correct options are
A $\frac{{\left[H^{+}\right]}_1}{{\left[H^{+}\right]}_2}$
C $\frac{C_1{\alpha }_1^2}{C_2{\alpha }_2^2}$

As we know, for acids, higher the dissociation, the higher is the hydrogen ion concentrations and acid will be stronger.

So, their strength can be compare by $\frac{{\left[H^{+}\right]}_1}{{\left[H^{+}\right]}_2}$

Also, we can compare their strength by their dissociation constants. Higher is the constant value, stronger is the acid for a weak acid. $K_a=C{\alpha }^2$

So, we can compare their strength by $\frac{K_{a1}}{K_{a2}}=\frac{C_1{\alpha }_1^2}{C_2{\alpha }_2^2}$.