Determine the amount of NaOH and Sr(OH)2 based on pOH

[ducmod]

Homework Statement

Hello!
I am trying to solve the following problem:
A 4.00-L base solution contains 0.100 mol total of

NaOH and Sr(OH)2 . The pOH of the solution is 1.51.

Determine the amounts (in moles) of NaOH and

Sr(OH)2 in the solution.

Homework Equations

3. The Attempt at a Solution [/B]
I am stuck because I am not sure I correctly constructing the solution path:

We have pOH = 1.51, which means that there are 10^(-1.51) moles of OH in solution, i.e. 0.0309 moles per one liter of solution. If I have 4 liters, then shouldn't there be 0.1236 moles of OH in this solution?
But according to the problem there are only 0.100 moles of NaOH and Sr(OH)2; both are strong bases, therefore there 0.100 moles of OH in the 4 liters of solution. How can that be?
Where is my mistake?
Thank you very much!

 

[Borek]

How many moles of OH^- are produced per 1 mole of dissociating Sr(OH)₂?

 

[ducmod]

How many moles of OH^- are produced per 1 mole of dissociating Sr(OH)₂?

2 moles. There are 3 moles of OH- produced by dissociating both NaOH and Sr(OH)2, and two of those come from dissociating Sr(OH)2

 

[Borek]

What does it mean

solution contains 0.100 mol total of NaOH and Sr(OH)2