Question

A buffer contains 0.17 mol of propionic acid ( C2H5COOH ) and 0.14 mol of sodium propionate (C2H5COONa) in 1.20 L.What is the pH of the buffer after the addition of 0.01 mol of HI

Answer 1

Answer: The pH of the buffer after addition of given amount of HI is 4.76

Step-by-step explanation:

We are given:

Initial moles of propionic acid = 0.17 moles

Initial moles of sodium propionate = 0.14 moles

Moles of HI added = 0.01 moles

The chemical equation for the reaction of HI and sodium propionate follows:

`C_2H_5COONa+HI\rightleftharpoons C_2H_5COOH+NaI`

Initial: 0.14 0.01 0.17

At eqllm: 0.13 - 0.18

Total volume of the container = 1.20 L

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

`pH=pK_a+\log(([salt])/([acid]))`

`pH=pK_a+\log(([C_2H_5COONa])/([C_2H_5COOH]))`

We are given:

`pK_a` = negative logarithm of acid dissociation constant of propionic acid = 4.87

`[C_2H_5COONa]=(0.14)/(1.20)`

`[C_2H_5COOH]=(0.18)/(1.20)`

pH = ?

Putting values in above equation, we get:

`pH=4.87+\log((0.14/1.20)/(0.18/1.20))\\\\pH=4.76`

Hence, the pH of the buffer after addition of given amount of HI is 4.76