Dilutions

Preparing Dilutions Concentrated solutions that are diluted before use to a specified concentration and volume are frequently used in the laboratory. However this can create a problem. How much of the stock do you remove and how much diluent do you add to it to produce a solution of a certain concentration and volume?

Dilution Factors Suppose that 10 mL of a stock solution is removed and is diluted with 40 mL of buffer. This is a 10 mL/50 mL dilution, which equals a 1/5 dilution (the units cancel). The dilution factor is “1/5”.

Dilutions & Proportional Relationships The concepts of dilution and proportion are related. For example: 0.1 mL of food coloring mixed with 9.9 mL of water is equivalent to 1 mL of food coloring mixed with 99 mL of water.

Preparing Dilutions Suppose you have a liter of 4 M stock solution of GPS buffer and you want to dilute some of it so that you have 200 mL of 500 mM GPS. There are various ways to do this, however, a helpful formula to use is: C 1 V 1 = C 2 V 2 Concentration 1 * Volume 1 = Concentration 2 * Volume 2

Applying C 1 V 1 = C 2 V 2 Consider first, is this a situation where a less concentrated solution is being made from a more concentrated solution? Yes. Therefore, it is appropriate to apply the M1V1= M2 V2 equation (*Note: ‘M’ is used for dilution problems involving molarity,‘C’ is used for problems involving ratio and percent concentrations).

Applying C 1 V 1 = C 2 V 2 1.) Concentrated solution = 2M = M1 2.) The volume of concentrated stock necessary is ? (what you want to calculate, how much stock to take out to make the desired dilution) = V1 3.) The concentration you want to prepare is 500 millimolar = M2 4.) The volume you want to prepare is 200 mL = V2 (in a real laboratory situation, you will decide what the volume will be)

Applying C 1 V 1 = C 2 V 2

C 1 V 1 = C 2 V 2 can also be used when preparing solutions with more than one stock involved. Simply determine V 1 for each component of the desired solution while using the desired final concentration and volume for C 2 V 2

Dilution Labs All these calculations and procedures will be much clearer after you do the Dilutions Lab!