# Two pH questions i don't understand

1. Oct 19, 2016

### AMan24

1. The problem statement, all variables and given/known data
1) Which solution has the higher pH, a 0.001 M solution of NaOH or a 0.001 M solution of Ba(OH)2?

2) Would a 1.0 × 10-8M solution of HCl have pH < 7,
pH = 7, or pH > 7? My professor said she shouldn't have put HCl as the solution, but that it doesn't matter apparently.

2. Relevant equations

3. The attempt at a solution
1) answer is: A 0.001 M solution of Ba(OH)2 has the higher pH

2) answer is: pH < 7

My question:

For 1) How do i determine this? I have no idea how

For 2) I'm doing pH = -log[1.0 x 10-8] and im getting pH = 8. How is the answer less than 7?

Last edited: Oct 19, 2016
2. Oct 19, 2016

### Bystander

Of what?
Are you conversant with the concepts of stoichiometry?

3. Oct 19, 2016

### AMan24

It was HCl but she said it doesn't matter.

Yes i know stoichiometry

4. Oct 19, 2016

### Bystander

And if the solute were a base? It matters.
What does stoichiometry tell you?

5. Oct 19, 2016

### AMan24

I guess I could find the number of moles of OH in each of the molecules using molarity. And the Ba(OH)2 would have 2x the number of moles. If that's right then I could also figure it out if it were two different molarities.

6. Oct 20, 2016

### epenguin

Answer to 2 follows directly from definition of pH, and the one you give, I don't know whether it is yours or what you were told, seems wrong to me.

For 1 you are on the right lines; what do you think are the molarities of everything that is there in that Ba(OH)2 solution?

Last edited: Oct 20, 2016