Question

Given below are the dissociation constant values of few acids. Arrange them in order of increasing acidic strength.

$F{e^{3 +}}_{(aq)} + 3O{H^{-}}_{(aq)}$

$Fe(OH)_{3(g)}$

• A. HCN < $K_{c} = \frac{\left\lbrack Fe(OH)_{3} \right\rbrack}{\left\lbrack Fe^{3 +} \right\rbrack\left\lbrack OH^{-} \right\rbrack^{3}}$< $K_{c} = \frac{\left\lbrack Fe(OH)_{3} \right\rbrack}{\left\lbrack Fe^{3 +} \right\rbrack\left\lbrack OH^{-} \right\rbrack}$< $K_{c} = \frac{1}{\left\lbrack Fe^{3 +} \right\rbrack\left\lbrack OH^{-} \right\rbrack^{3}}$
• B. $K_{c} = \left\lbrack Fe(OH)_{3} \right\rbrack$ < $P_{4(s)} + 5O_{2(g)}$< HCN < $P_{4}O_{10(s)}$
• C. $K_{c} = \frac{\left\lbrack P_{4} \right\rbrack\left\lbrack O_{2} \right\rbrack^{5}}{\left\lbrack P_{4}O_{10} \right\rbrack}$ < HCN < $K_{c} = \frac{1}{\left\lbrack O_{2} \right\rbrack^{5}}$ < $K_{c} = \frac{\left\lbrack P_{4}O_{10} \right\rbrack}{\left\lbrack P_{4} \right\rbrack\left\lbrack O_{2} \right\rbrack^{5}}$
• D. $K_{c} = \left\lbrack O_{2} \right\rbrack^{5}$< $K_{c}$< $Q_{c}$< HCN

Answer 1

Answer: (A)

HCN < $K_{c} = \frac{\left\lbrack Fe(OH)_{3} \right\rbrack}{\left\lbrack Fe^{3 +} \right\rbrack\left\lbrack OH^{-} \right\rbrack^{3}}$< $K_{c} = \frac{\left\lbrack Fe(OH)_{3} \right\rbrack}{\left\lbrack Fe^{3 +} \right\rbrack\left\lbrack OH^{-} \right\rbrack}$< $K_{c} = \frac{1}{\left\lbrack Fe^{3 +} \right\rbrack\left\lbrack OH^{-} \right\rbrack^{3}}$

Answer 2

: Acidic strength,$\propto \sqrt{K_{a}}$