Question

C

A scientist wants to make a solution of tribasic sodium phosphate, \rm Na_3PO_4 , for a laboratory experiment. How many grams of \rm Na_3PO_4 will be needed to produce 300. {\rm mL} of a solution that has a concentration of \rm Na^+ ions of 1.20 {\rm \it M} ?

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

Answer 1

Trisodium phosphate (Na₃PO₄) ------> 3 Na⁺ + PO₄^3-

1 mole of Na₃PO₄ ------> 3 moles of Na⁺ and 1 mole of PO₄^3-

x mole of Na₃PO₄ ------> 1.20 moles of Na⁺

mole of Na₃PO₄ (x) = 0.4 moles

Molar mass of Na₃PO₄= 163.94 g/mol

WKT, Mole= wt. of Na₃PO₄/ M.wt. of Na₃PO₄) (1000 mL /300mL)

or wt. of Na₃PO₄= (Mole of Na₃PO₄ x 300 mL)/ M.wt. of Na₃PO₄ x 1000 mL

wt. of Na₃PO₄= (0.4 mol x 300 mL x 163.94 g/mol) / 1000 mL= 19.6728 g or 19.7 g of Na₃PO₄ will be needed to produce 300mL of a solution.