Question

What is the pH of a 75.0 mL solution that is 0.047 M in weak base and 0.057 M in the conjugate weak acid ( K a = 7.2 × 10 − 8 ) ?

Answer 1

Answer: The pH of the buffer is 7.22

Explanation:

To calculate the pH of acidic buffer, we use the equation given by Henderson Hasselbalch:

$pH=pK_a+\log(\frac{[\text{conjugate acid}]}{[\text{weak base}]})$

We are given:

$pK_a$ = negative logarithm of acid dissociation constant = 7.14

$[\text{conjugate acid}]=0.057M$

$[\text{weak base}]=0.047M$

pH = ?

Putting values in above equation, we get:

$pH=7.14+\log(\frac{0.057}{0.047})\\\\pH=7.22$

Hence, the pH of the buffer is 7.22