Question

5 points Explain why the pH of a strong acid whose concentration if 1.0 x 10-8 M must have a pH that is less than 7.

Answer 1

It is because H^+ ions from water can't be neglected. H^+ from water as well as from acid should be considered for calculating pH.

The H^+ ions from the water suppress the degree of the dissociation of the strong acid due to the common ion effect.

So, the H^+ concentration of the strong acid will get decreases. The concentration of (1.0*10^-8) will get decreases to some extent that will effect it's pH value and due to this, the pH generally comes just less than 7 for such acid.

Suppose HA is the strong acid, HA 1.0x108 M 1.0x10 8 : 1.0x100 HO 7 H+ + OH x+ ! LOX10-8 commonion o's [H+] = 1.0 x108 + x Kw = [H + ] [ou] 1014 = [1.0 X10-8 + x] [ve] 10-14 = 1.0x10x + x² on x² + 1.0x108 - 10-14 = 0 On solving x < 108 M Mence pH = -log [ht] we get pH just less than 7.