A solution of a pH of 4 has 10 times the concentrations of H+ present compared to a solution with a pH of 5, where;
pH = - log [H+], the concentration of H+ of pH=4 is:
[H+] = anti Log (- pH) = 10 ^ - pH = 10 ^ - 4 = 0.0001 M >>>>> (1)
the concentration of H+ of pH = 5 is
10^ -5 = 0.00001 M >>>>> (2)
So, (1) more than (2) by 10 times