Question

a Solution is prepared by diluting 450 mL of 0.773 M cobalt(11) chloride solution with water to a final volume of 1.25 L.

a) calculate the molarities of cobalt (II) and chloride ions in this solution

b) determine the mass of cobalt (II) chloride that was dissolved to give the original solution

Answer 1

First calculate the molarity of CoCl2 in the solution as follows:

M1V1=M2V2

V1 = 450 mL = 0.450L

0.450 L of 0.773 M = M2*1.25 L

M2 = 0.278 M

CoCl2 --- > Co 2+    + 2Cl-

0.278 M CoCl2   gives --- > 0.278 M Co2+

0.278 M CoCl2   gives --- > 0.556 M Cl-

one mole od CoCl2 give two mole of Cl-

To determine the mass of cobalt (II) chloride that was dissolved to give the original solution first calculate the moles of cobalt (II) chloride as follows:

0. 450 L * 0.773 M = 0.348 mol cobalt(11) chloride

Now calculate the amount of 0.348 mol cobalt(11) chloride:

0.348 mol cobalt(11) chloride * molar mass

=0.348 mol* 129.839 g/mol

=45.2 g cobalt(11) chloride