Calculating pH of Na3PO4 (45.0g/L): Find the Basicity

[future_vet]

We have 45.0g of Na3PO4 per liter. We know it is very basic but need the pH.
I don't have the answers to all exercises, so if you could check my work, that'd be great.

So, we have g, but moles would be more useful.
So 45g x (1 mol/163.937) = 2.7 x 10^-1 mol.

We know that strong bases completely dissociate in water.
Therefore, [Na3PO4]=[OH-].
So, since pOH = - log of all that = 0.569
Therefore: pH = 14 - 0.569 = 13.431 which is indeed pretty basic.

Any mistake somewhere?

Thank you,

Joanna.

 

[Borek]

PO4-3 is not that strong base and pH is slightly lower. You have to calculate pOH assuming it is a weak base.

pH of weak acid or base

pH cheat sheet

 

[GCT]

You need to incorporate the equilibrium constant toward solving this problem.

 

[future_vet]

We do not have the equilibrium constant, and if they don't give us and don't tell us to refer to a table, it means we have to find a way around it (without an ICE table)...

 

[Borek]

No way. You will either use dissociation constant or it'll be pure guesswork.

 

[future_vet]

That's exactly why I assumed that, since they said that it was very basic, it completely dissociated in H2O, and it's why I went on with calculations without an ICE table.

Well, I'll just assume it's right and see what the correction is when we get it.