Question

Anything with a Ph level of 7 is neutral. Anything lower than 7Ph is an acid and anything higher than Ph level 7 is a base. So 1 litre of Ph 7 + 1 litre of Ph 1 = Ph 8 or Ph 6?

Answer 1

pH is defined as negative log of H⁺ concentration in solution. When we mix two solution with different pH, the pH of resulting solution is also calculated by the H⁺ ion concentration in resulting solution. It is not simply the addition of two volumes.
Let us calculate it.
[H⁺] for solution with pH = 1 is 10^-1 M
[H⁺] for solution with pH = 7 is 10^-7 M
Since, equal volumes of the given solutions are mixed; concentration will be halved.
Therefore,
[H⁺]= 10^-1 + 10^-7/2
= 10^-1(1 + 10^-6)/2
= 1.0 x 10^-1/2
= 5.0 x 10^-2 M
pH = -log [H+]
= - log [5 x 10^-2 M]
= 1.3