how to calculate the ph?

Question

Calculate [OH -], pOH, and pH for each of the following.
(a) 0.00035 M Ca(OH)2
[OH -]
M
pOH

pH

(b) a solution containing 19 g of KOH per liter
[OH -]
M
pOH

pH

(c) a solution containing 190.0 g of NaOH per liter
[OH -]
M
pOH

pH

HOW DO YOU DO IT? thanks!

Answer 1

Doing (a), all the compound ionizes, so the conc of OH- is 7x10-4 M. p(OH) is 4-log 7 = 3.15 appx
pH is then 10.85, since pH+pOH=14 at 25degC.