The pH of a solution is a measure of the acidity of a solution and is logarithmically related to the hydrogen ion concentration. It is expressed as:
pH = -log [H+]
We use this to determine the amount of H+ needed to adjust the pH to the desired value.
pH1 = 7.2 = -log [H+]
[H+] = 6.31x10^-8
pH2 = 8.2 = -log [H+]
[H+] = 6.31x10^-9
[H+] to be added = 6.31x10^-8 - 6.31x10^-9 = 5.68x10^-8 M
She should add an acidic solution with concentration 5.68x10^-8 M. Hope this helps.
