posted by Anonymous .
A 0.2481 g sample of marble was dissolved in 100 mL, and a 10.00 mL aliquot of the solution was titrated to an end point with 23.56 mL of 0.01052 M EDTA solution. What is the molecular weight?
I know how to start this problem. Any help is appreciated!
Why didn't you show what you know and let us help you from there?
M EDTA x L EDTA = moles EDTA.
moles EDTA = moles marble.
moles marble x molecular weight = grams.
Solve for molecular weight.
(0.01052 M EDTA)(.02356 L) =2.48 x 10^-4 mol EDTA or marble
2.48 x 10^-4 mol marble x _g/mol =0.2481g
molecular weight = 1000 g/mol
so I don't do anything with the 10-ml aliquot of soln?
Sure. Since it was a 10 mL aliquot, the moles in the original sample is 10 times the moles of the titration. Dividing your answer by 10 gets 100 for the molecular weight which is close. (Dividing you answer by 10 is the equivalent of multiplying the moles by 10.) Since you have four significant figures, you need one more place to the 100.something.
wouldn't the units be off? g/mol*ml
mL EDTA x M EDTA = moles EDTA in 10 mL.
Moles EDTA in 10 x (100 mL/10 mL) = moles EDTA to titrate the original sample.
moles EDTA to titrate the original sample = moles marble in the original sample.
moles marble x molecular weight marble = grams marble.
thanks for the help DrBob222!