Question

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 638 mL of a solution that has a concentration of Na+ ions of 0.603 M ?

Enter a numerical answer only, in terms of grams.

Answer 1

Given

Molarity of Na+ ions = 0.603 M ( or mol/L)

Volume = 638 ml = 0.638 L

No. of moles of Na+ = Molarity of Na+ ions * Volume = 0.638 L * 0.603 mol/L = 0.385 moles of Na+ ions

1 moles of Na3PO4 will produce 3 Na+ ions when dissolved in water

so 0.385 Na+ ions will be produced when 0.385 / 3 = 0.128 moles of Na3PO4

Molar mass of Na3PO4 = 164 g/mol

Mass of Na3PO4 required = No. of moles of Na3PO4 * molar mass of Na3PO4 = 0.128 moles * 164 g/mol

Mass of Na3PO4 required = 21 g

we need 21 g of Na3PO4