I have several issues with a).
That's 1.694 mg CoSO4; when you convert that to 0.001694 that is now g/mL and not mg. Second where you have 1*10^-6 mol you threw away the other 3 places. The 1.695 is to four places and you should have 4 places in the answer.
So 1.694E-3 g/mL x 25 mL x (1 mol/155.0g) = 2.732E-4 mols EDTA needed.
M = mols/L and L = mols/M =
2.732E-4/0.008640 = ?L and convert to mL if needed.
A solution contains 1.694 mg of CoSO4 (MW 155.0) per mL. Calculate
a) The volume of 0.008640 M EDTA needed to titrate a 25.00 ml aliquot of this solution.
moles CoSO4 = 0.001694mg/ 155 g/mol
= 1*10^-6 mol
Moles EDTA = 1*10^-6mol/0.025L
= 0.000436 mol/L (in 25 mL)
This is where I got stuck.
b)The volume of 0.009450 M Zn2+ solution needed to titrate the excess reagent after the addition of 50.00 mL of the EDTA solution to a 25.00 mL aliquot of the Co2+ solution.
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