Posted by Anonymous on .
A chemist wants to prepare a stock solution of H2SO4 so that a sample of 20.00mL will produce a solution with a concentration of .50 M when added to 100.0mL of water.
A)what should the molarity of the stock solution be?
B)If the chemist wants to prepare 5.00L of the stock solution from a concentrated H2S)4, which is the 18.0 M, what volume of concentrated acid should be used?
(please explain how you get the answer..I'm so confused, help!!)

Chemistry!! 
DrBob222,
A. The easy way is to use the dilution formula. Also you MUST assume that the volumes are additive.
mL1 x M1 = mL2 x M2
0.5 x 120 = 20 x M2
M2 = 0.5 x 120/20 = 3M
B. Use the dilution formula again.
18M x mL1 = 5,000 mL x 3M.
Solve for mL1 which is volume of th 18 M stuff. 
Chemistry!! 
Anonymous,
BJB