Question

Find the PH of a solution made up of 0.05M sodium citrate and 0.2M citric acid?

Answer 1

This given solution is made up of tow constituents, one base - sodium citrate and one acid - citric acid.  Since volume is not given, we will assume the volume to be 1 ml.

The resultant pH of the solution is derived by adding the pH of the two constituents divided by the volume. Since volume is 1 here, our calculation has become easy.

First find the pH of 0.2 M citric acid.

pH = - ( log 0.2)

= 0.698 ..................................  (1)

Now, calculate pH of 0.05 M sodium citrate ( base)

For this, first find out pOH value for the given base and then subtract it from 14.

pOH = -log( 0.05 )

= 1.301

pH = 14 - 1.301

= 12.699 ........................................ (2)

The resultant pH  is 0.698 + 12.699 = 13.397

So the answer is 13.397.