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 500 mL of a solution that has a concentration of Na+ ions of 0.700 M

Answer 1

You want 0.700M in Na^+ which means 1/3 of that for Na3PO4 or 0.700/3 = ??
How many moles do you want? That will be ??M x L = xx moles.
How many grams is that.
moles = grams/molar mass.