Hard water often contains dissolved C^2+_a and Mg^2+ ions. One way to soften wat

Question

Hard water often contains dissolved C^2+_a and Mg^2+ ions. One way to soften water is to add phosphates The phosphate ion forms insoluble precipitates with calcium and magnesium ions removing them from solution Suppose that a solution is 4.5 times 10^-2 M in calcium chloride and 8.0 times 10^-2 M in magnesium nitrate. What mass of sodium phosphate would have to be added to 2.0 L of this solution to completely eliminate the hard water ions? Assume complete reaction. Express your answer using two significant figures.

Explanation / Answer

M = 4.5*10^-2 + 8*10^-2 = 0.125 M of X+2

then

3X+2 + 2PO4-3 = X3(PO4)2

then

ratio is 2/3

2/3*0.125 = 0.0833 M of PO4-3

then

0.0833 M of Na3(PO4)

mol = MV = 0.0833*2 = 0.1666 mol

mas s= mol*MW = 0.1666*163.94 = 27.312404 g of Na3PO4 needed

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