You need to make 1.5L of 1.0M HCl from a stock solution of 12.0M HCl. How many L of the stock solution do you need?

125 ml of HCl

Explanation:

The molarity of the stock solution to determine how many milliliters would contain 1.5 moles of HCl. Since a concentration of 12.0 mol/L means that you get 12.0 moles of hydrochloric acid per liter of solution,  

Concentration of required HCl (C1)  = 1.0M

Volume of required HCL (V1)  = 1500 ml

Concentration of stock HCl (C2)  = 12M

Volume of stock  HCL (V2)  = ?

C1V1 = C2V2

V2 = C1V1/C2 = 1*1500/12 = 125 ml

the answer is symmetrical : )