Question

What is the pH and pOH of 6.5 g of sodium hydroxide in 650 mL of water?

Answer 1

`pH+pOH=14` in aqueous solution.

Explanation:

And since, `pOH=-log_10[HO^-]`, all we have to do is calculate the concentration of `HO^-`.

`[HO^-]=((6.5*g)/(40.00*g*mol^-1))/(650xx10^-3*L)=0.25*mol*L^-1`

So `pOH=-log_10(0.25)=-(-0.60)=0.60`

And `pH=13.4`

Spare a thought for the students who did these calculations in the days before electronic calculators. Some 30-40 years ago, students of mathematics, and physics, and chemistry, would routinely use logarithmic tables for these calculations.