# Find the (H3O+) AND THE (OH+) in pH 2.5. Determine pH and pOH of .01 M sodium hydroxide.

jerichorayel | College Teacher | (Level 2) Senior Educator

Posted on

The pH system is used to measure the degree of acidity of any acids ar bases. It can be solved using this expression:

`pH = -log [H^+]`

For the measure of hydroxide we use the pOH which is pretty similar with the above expression:

`pOH = -log [OH^-]`

the relationship of pH and pOH is:

`pH + pOH = 14`

If the pH or pOH is given instead the concentration, we can arrange the expressions as:

`pH = -log [H^+]`

`[H^+] = 10^(-pH)`

AND

`pOH = -log [OH^-]`

`[OH^-] = 10^(-pOH)`

For pH 2.5:

`pH + pOH = 14`

`pOH = 14- 2.5`

`pOH = 11.5`

`[H^+] = 10^(-pH)`

`[H^+] = 10^(-2.5)`

`[H^+] = 3.16x10^-3`

`[OH^-] = 10^(-pOH)`

`[OH^-] = 10^(-11.5)`

`[OH^-] = 3.16x10^-12`

For 0.01 sodium hydroxide (NaOH)

Since it is a base, we should measure the pOH first.

`pOH = -log [OH^-]`

`pOH = -log [0.01]`

`pOH = 2`

`pH = 14-2`

`pH = 12`

Sources: