How would you prepare 100.0 mL of 0.400 M CaCl2 from a stock solution of 2.00 M CaCl2?

Measure 20mL of the stock

Explanation:

All we need to do is to find the volume of the stock solution needed. This is illustrated below:

C1 = 2M

V1 =?

C2 = 0.400 M

V2 = 100mL

C1V1 = C2V2

2 x V1 = 0.4 x 100

Divide both side by 2

V1 = ( 0.4 x 100) /2

V1 = 20mL

Therefore, to prepare the solution, we will measure 20mL of the stock solution and make it up to the 100mL mark.