Prove that degree of dissociation of a weak acid is given by: α = 1 1 + 10 pK a - pH where K a is its dissociation constant.

For a weak monoprotic acid HA ⇌ H + + A - Before dissociation 1 0 0 After dissociation 1 - α α α H + = Cα . . . . . ( i ) and K a = Cα 2 ( 1 - α ) . . . . . . . ( ii ) By substituting value of C from Eq. ( ii ) in Eq. ( i ) H + = K a · ( 1 - α ) · α α 2 = K a ( 1 - α ) α . . . . . . ( iii ) Thus, - log H + = - log K a + log ( 1 - α ) - log α or pH = log 1 K a + log α ( 1 - α ) . . . . . ( iv ) Also, pH = pK a - log 1 - α α or log 1 - α α = pK a - pH 1 - α α = 10 pK a - pH or 1 α - 1 = 10 pK a - pH or α = 1 1 + 10 pK a - pH

Prove that degree of dissociation of a weak acid is given by: α = 1 1 + 10 pK a - pH where K a is its dissociation constant.

For a weak monoprotic acid HA ⇌ H + + A - Before dissociation 1 0 0 After dissociation 1 - α α α H + = Cα . . . . . ( i ) and K a = Cα 2 ( 1 - α ) . . . . . . . ( ii ) By substituting value of C from Eq. ( ii ) in Eq. ( i ) H + = K a · ( 1 - α ) · α α 2 = K a ( 1 - α ) α . . . . . . ( iii ) Thus, - log H + = - log K a + log ( 1 - α ) - log α or pH = log 1 K a + log α ( 1 - α ) . . . . . ( iv ) Also, pH = pK a - log 1 - α α or log 1 - α α = pK a - pH 1 - α α = 10 pK a - pH or 1 α - 1 = 10 pK a - pH or α = 1 1 + 10 pK a - pH

The exothermic formation of ClF 3 is represented by the following equation: Cl 2 g + 3 F 2 g ⇌ 2 ClF 3 g ; ΔH = - 329 kJ Which of the following will increase the quantity of ClF 3 in the equilibrium mixture of Cl 2 , F 2 and ClF 3 ?

Increasing the volume of the container.

E M B I B E

Alpha Question Bank for Engineering: Chemistry>Chapter 5 - Equilibrium>Exercise-1>Q 175

HARD

JEE Main/Advance

IMPORTANT

Earn 100

Prove that degree of dissociation of a weak acid is given by: $α = \frac{1}{1 + 10^{({pK}_{a} - pH)}}$ where $K_{a}$ is its dissociation constant.

Important Questions on Equilibrium

EASY

JEE Main/Advance

IMPORTANT

Alpha Question Bank for Engineering: Chemistry>Chapter 5 - Equilibrium>Exercise-1>Q 177

Whose

pH

increases by greater value on dilution from initial

pH = 2

?
(a)

{CH}_{3} COOH

solution
(b)

HCl

solution.

MEDIUM

JEE Main/Advance

IMPORTANT

Alpha Question Bank for Engineering: Chemistry>Chapter 5 - Equilibrium>Exercise-1>Q 180

A $0.25 M$ solution of pyridinium chloride $C_{5} H_{5} {NH}^{+} {Cl}^{-}$ was found to have a $pH$ of $2.75$ . What is $K_{b}$ for pyridine, $C_{5} H_{5} N$ ?