Question

A 5g mn sample was dissolved in 100ml water. If the percentage of M (At wt =55g/mol) in the sample is about 5%. What volume is needed to prepare 100ml of approximately 3.0 x 10-3 M solution


Who helps for me. The right answer 6.7ml

Answer 1

If I interpret the problem correctly the 5g Mn sample is only 5% pure; therefore,
mass Mn = 5g x 0.05 = 0.25 g Mn.
mols Mn = 0.25/55 = about 0.0045 and that in 100 mL is 0.0045/0.1 = 0.045M
Then c1v1 = c2v2
0.045M*v1 = 0.003M*100 mL
Solve for v1.