Question

A highly concentrated ammonia solution is found to have a pH of 12.03. What is the hydroxide concentration, [OH-(aq)] in mol L-1?

Answer 1

0.01348 M (mol L-1)

Step-by-step explanation:

Water can be autoionized:

H2O + H2O ⇄ H3O+ + OH-

This a reversible reaction and then it has a unique constant Kw that at 25ºC it takes the value of 10^-14

`10^(-14) =[H_(3) O+][OH-]`

pH is the concentration of [H3O+] ions in a logaritmic scale:

`pH = -log([H_(3)O+]`

Then you can solve for the [OH-]

`[OH-]=(Kw)/(10^(-pH))=(10^(-14))/(10^(-12.03))=0.01348 M`

Hope it helps!