find pH given OH-

Question

What is the pH of a solution containing 0.3 g/L OH-?

Answer 1

First we have to change 0.3 g/L OH- to mols/L.

To do this we have to find the molar mass of OH-. Look at the mass of oxygen and hydrogen on the periodic table and add them together. This will be x for our next equation. Now we can set up our conversion.

 0.3 g of OH-/L (1 mol of OH-/x g of OH-)= our mol/L concentration of OH-

 

 

 

In order to find pH, there is an equation we need. 

 

pH=-log[H3O+] 

 

Since we are given the concentration of OH-, we have to use another formula to find the pOH and then we can subtract the pOH from 14. 

 

pOH=-log(OH-)

In this equation we use the new mol/L concentration we found in our first conversion. 

 

Then plug the answer which is the pOH into this equation, 14-pOH=pH.

 

This should give us our answer. If you have any questions, feel free to ask.