What is the pH of a 6.0 x 10^-12 solution of HCl (Hydrochloric acid) at 25°C

What is the pH of a 6.0 x 10^-12 M solution of HCl (Hydrochloric Acid) at 25°C?

The answer choices are:
A) 7
B) 9
C) 5
D) 11
E) 1

I thought it was D.. but the answer key says it's A. Can someone show me how to get A?

You cannot forget that pure water has a [H^+] = 1.00 x 10^-7 M This is often an error that is made.

If you have [H^+] = 6.0 x 10^-12 M then you are adding this amount to 1.00 x 10^-7. The additional amount is insignificant.

Look at it this way:

[H^+] = 0.000000700 + 0.0000000000060 = 0.000000700006 M

The amount added to the solution by the HCl solution is insignificant.

pH = -log(1.00 x 10^-7) = 7

The answer is A).

Hope this is helpful to you. JIL HIR

pH= -log[H+]
pH=-log[6E-12]
pH= 11.2
ans D)