Question

14. What minimum mass of cobalt(II) nitrate must be added to 60.0 mL of a 0.0890 M phosphate solution in order to completely precipitate all of the phosphate as solid cobalt(II) phosphate? 2PO4 (aq) + 3Co(NO3)2(aq) - Co3(PO4)2(s) + 6NO3 (aq)

Answer 1

lets calculate the mol of PO43-

volume , V = 60 mL

= 6*10^-2 L

use:

number of mol,

n = Molarity * Volume

= 8.9*10^-2*6*10^-2

= 5.34*10^-3 mol

According to balanced equation

mol of Co(NO3)3 reacted = (3/2)* moles of PO43-

= (3/2)*5.34*10^-3

= 8.01*10^-3 mol

This is number of moles of Co(NO3)3

Molar mass of Co(NO3)3,

MM = 1*MM(Co) + 3*MM(N) + 9*MM(O)

= 1*58.93 + 3*14.01 + 9*16.0

= 244.96 g/mol

use:

mass of Co(NO3)3,

m = number of mol * molar mass

= 8.01*10^-3 mol * 2.45*10^2 g/mol

= 1.962 g

Answer: 1.96 g