Chemistry
posted by Cory on .
A scientist wants to make a solution of tribasic sodium phosphate, Na_3PO_4, for a laboratory experiment. How many grams of Na_3PO_4 will be needed to produce 375 mL of a solution that has a concentration of Na^+ ions of 1.10M?
I tried multiplying .375 L by 1.10 M to get the number of moles, but I don't know if I'm doing this correctly. I got 0.4125 mols. Then am I supposed to convert this to grams? I feel like the moles number should be bigger.

There are two or three ways of starting and yours is as good as any. What you have done is ok. I assume you need help with the next step.
moles = M x L and 0.4125 moles is correct. But note that this is moles Na^+ and NOT Na3PO4. So moles = grams/molar mass or grams = moles x molar mass. Thus, grams = 0.4125 x molar mass Na3PO4 will give you the grams of Na3PO4. Since there are 3 Na^+ for every mole of Na3PO4, you want to divide this number by 3. You can check to see if this number is right by dividing grams Na3PO4 by molar mass, and dividing that by 0.375 to obtain molarity Na3PO4. Then multiply by 3 to obtain molarity Na^+. 
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 475 mL of a solution that has a concentration of Na^+
ions of 0.800 M?
Express your answer numerically in grams.
mass of Na3PO4 = 
0.8g