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 1.00 M?

Express your answer to three significant figures and include the appropriate units.

137g of Na3PO4

Explanation:

We sort of need to work backwards in this case. First figure out how many total Na + ions there will be:

C = n/V

1 = n/0.4

n=2.5

The solution will contain 2.5 moles of Na + ions. Now, notice that in Na3PO4 there are 3 Na atoms per molecule. That means if there are 2.5 moles of Na, there are 3 times LESS moles of Na3PO4.

2.5/3 = 0.833

Therefore 0.833 moles of Na3PO4 will be required. Now it's just a simple matter of converting to grams (using molar mass of Na3PO4):

n = m/MM

0.833 = m/164

m = 137

A total of 137g of Na3PO4 will be required.