Question

How much water should be added to 45.0 mL of 0.225 M HCl to dilute the solution to 0.155 M?

i did .225M x .045L / .155M = 65mL

so wouldnt 20 mL be added?

Answer 1

M1*V1 = M2*V2
(0.225M)(45.0mL) = (0.155M)(V2)
Solve for V2 and subtract 45.0 to get the volume of water that must be added to get the final volume.