How many mL of 12.0 M HCL are needed to make 2.0 L of 0.40 M HCl solution?

Answer 1

A 0.40 M solution means it has 0.40 moles of HCl in 1 liter so since you want 2 liters, you will be getting (ending up with) 0,80 moles of HCl.

In order to get 0,80 moles of HCl from a 12.0 M solution we would say:

(12 moles/liter)(x liters) = 0.80 moles

x = 0.8/12 = 1/15 liters or approx 0.067 liters or approx 67 mL of the 12 M solution. The rest would be water.