A 0.500 l solution of 6 m hcl has to be made. how much 12 m hcl is needed?

The answer is 0.250 L.

The starting solution:

V1 = ?

C1 = 12 M

The final solution:

V2 = 0.500 L

C2 = 6 M

V1 * C1 = V2 * C2

V1 * 12 M = 0.500 L * 6 M

V1 = 0.500 L * 6 M / 12 M

V1 = 0.250 L