To how much water should 250 mL of 12 M hydrochloric acid be added to

produce a 4.0 M solution?

500 mL water

Explanation:

M1V1 = M2V2

M - molarity, V - volume of solution before adding water

M1 = 12MV1 = 250 mL

M2 = 4.0 M

12M * 250 mL = 4.0*V2

V2 = 12*250/4.0 = 750 mL of solution should become after adding water

750 mL - 250 mL = 500 mL of water should be added