[rice noodles]

Hey guys,

I'm doing a review of highschool chemistry topics and this question confuses me:

"A scientist wants to make a solution of tribasic sodium phosphate, Na₃PO₄, for a laboratory experiment. How many grams of Na₃PO₄ will be needed to produce 400. mL of a solution that has a concentration of Na+ ions of 0.800 M ?
Express your answer to three significant figures and include the appropriate units."

I figured I could just use M=n/v and plug in the numbers like so -> (0.800 M) = n/(0.400 L). I converted the value of "n" into grams and got an answer of 52.5 grams of Na₃PO₄. I thought this was correct because tribasic sodium phosphate had a 1:1 ratio between its components. Could someone please tell me why I'm incorrect?

[sjb]

Try working it backwards. What is the molar concentration of a 400 ml solution of Na₃PO₄ that contains 52.5 grams of salt.

[Borek]

tribasic sodium phosphate had a 1:1 ratio between its components

Care to elaborate?

Your solution is 0.8 M in PO₄^3-.

[chenbeier]

to produce 400. mL of a solution that has a concentration of Na+ ions of 0.800 M ?

I think the sodium is 0,8 M not the phosphate, this would be 0.267 M.