[fchs]

What mass of Na3PO4 (dot in middle) 12 H2O would be needed to prepare0.250 L of a solution in which the Na +ion concentration is 0.250 moles per liter?


I've been doing good with molarity problems, but this is the first I've had to work that mentioned ions.

Can someone please explain what to do with this problem?

Any help is appreciated.

Thanks

[Borek]

Imagine dissolving 1 mole of Na₃PO₄. How many moles of Na⁺ will be present in the solution?

[fchs]

Imagine dissolving 1 mole of Na₃PO₄. How many moles of Na⁺ will be present in the solution?

I'm confused because it says the Na+ ion concentration is 0.250 moles per liter..

I just don't understand at all what to do with this problem

[Borek]

Try to answer my question. Don't think about 0.250M yet.

[fchs]

I'm still stumped because to get moles you go

? g Na x 1 mol Na/ ?g Na =? mol Na

? g Na x 1 mol Na/ (3 x 22.99 = 69.37) = ? mol Na

But I don't know what grams to start with....

[enahs]

You know for every moles of Na₃PO₄ ^. H₂O you get 3 moles of Na⁺, correct?

Now, all you have to do is find how many moles of Na⁺ you want. Can you do that?

You then know for every 3 moles of Na+ you want, you need 1 mol of Na₃PO₄^.H₂O.

[fchs]

You know for every moles of Na₃PO₄ ^. H₂O you get 3 moles of Na⁺, correct?

Now, all you have to do is find how many moles of Na⁺ you want. Can you do that?

You then know for every 3 moles of Na+ you want, you need 1 mol of Na₃PO₄^.H₂O.

I'm sorry I'm so lost, but I'm new to this chemistry thing and we just started this section Monday. I was doing fine until the question was changed a bit with the ions.