Question

If concentration of two weak acids are different and degree of ionization $\left(\alpha \right)$ is very less, then their relative strength can be compared by:

• A. $\frac{[H^{+}{]}_1}{[H^{+}{]}_2}$
• B. $\frac{{\alpha }_1}{{\alpha }_2}$
• C. $\frac{C_1{\alpha }_1}{C_2{\alpha }_2}$
• D. $\frac{K_{a_1}{C}_1}{K_{a_2}{C}_2}$

Answer 1

Answer: (A), (C)

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

The Relative strength (R.S) $=\frac{\left[H^{+}\right]furnishedbyacidI}{\left[H^{+}\right]furnishedbyacidII}=\frac{C_1{\alpha }_1}{C_2{\alpha }_2}=\frac{C_1}{C_2}\times \sqrt{\frac{K_{a_1}{C}_2}{K_{a_2}{C}_1}}=\sqrt{\frac{K_{a_1}{C}_1}{K_{a_2}{C}_2}}$
Relative strength of various acids can be compared using $K_a$, larger the value of $K_a$, the stronger the acid.
So their relative strength can be compared by $\frac{[H^{+}{]}_1}{[H^{+}{]}_2}$ or $\frac{C_1{\alpha }_1}{C_2{\alpha }_2}$.