a solution contains 1.569mg of CoSO4 (155g/mol)per milliliter. calculate the volume of 0.009275M Zn needed to titrate the excess reagent after addition of 50 ml of 0.007840M EDTA to a 25ml aliquot of this solution
I will use just two places but you can (you should) recalculate eac of these. I'm not working the complete problem; I'm just showing you how it's done.
Total CoSO4 = 1.6 mg CoSO4/mLx 25 mL = approximately 40 mg = 0.040 g.
mols CoSO4 in that 25 mL aliquot = 0.04/155 = approx 0.00026 moles.
mols EDTA added = M x L = 0.0078 x 0.050 = 0.00039
1 mol EDTA complexes 1 mol EDTA; therefore,
moles EDTA in excess = 0.00039 - 0.00026 = 0.00013
1 mol EDTA complexes 1 mol Zn; therefore, you will need to add 0.00013 moles Zn^2+. M = moles/L; Rearrange to L = mols/M = 0.00013/0.000784 = ?L about 0.16 L
Check my arithmetic closely. Those leading zeros can get confusing.