What is pH of .2M HCl?

Question

and how do you do this calculation?

Answer 1

Since HCl (Hydrochloric acid) is a strong acid, it dissociates completely in water and it won't have an acid dissociation constant. That means you can simply take it's concentration and take the negative log of it:

pH = - log (0.2)

Plug it into ur calculator and you'll get: 0.6989 or about 0.7

If you have studied algebra or precalculus you can further simplify the expression as such:

pH = - log (2 / 10)

Remember that log (a / b) = log a - log b

pH = - log 2 - - log 10

pH = - log 2 + log 10

pH = log 10 - log 2

Remember that log 10 = 1 since log w/o any base is assumed to be base 10

pH = 1 - log 2

Plug log 2 in ur calculator and you get: 0.301

pH = 1 - 0.301 = 0.699 or about 0.7  

Answer 2

pH = -log[H^+]

pH = -log (0.2)= -log(10^-1 * 2) (product rule)

pH= 1 - log2

pH = 1- 0.3010 = 0.6990