Question

You are given a 5M solution and you need to make the following dilutions: 1 M, 100 mM, and 25 mM.

4A. What is the dilution factor for each of these dilutions?

4B. If you need 5 mL of each of the diluted solutions, how much of the 5M stock would you use, and how much water would you add? Show your work.

Answer 1

4A. Given a 5 M stock solution

Dilution factor is defined as the ratio of original concentration to final concentration.

For 1 M solution,

dilution factor would be = 5/1 = 5

For 100 mM solution,

dilution factor would be = 5/0.1 = 50

For 25 mM or 0.025 M solution,

dilution factor would be = 5/0.025 = 200

4B. If final volume V2 is 5 mL then,

For 1 M we would need,

Using M1V1 = M2V2

where,

M1 = 5 M

V1 = unknown

M2 = 1 M

V2 = 5 mL = 0.005 L

Feed the values,

5 x V1 = 1 x 5

V1 = 1 mL of stock solution diluted to 5 mL would give a 1 M solution. So we would need 1 mL of stock solution and 4 mL of water to get a final solution of 1 M concentration and 5 mL volume.

For 100 mM,

5 x V1 mL = 0.1 x 5 mL

V1 = 0.1 mL of 5 M stock diluted to 5 mL with 4.9 mL H2O would give a 100 mM solution

For 25 mM (0.025 M) solution,

5 x V1 mL = 0.025 x 5 mL

V1 = 0.025 mL of 5 M stock solution diluted with 4.975 mL H2O of total 5 mL would result in a 25 mM solution.