Dilution Chemistry
In chemistry and biology we often need to make a dilute solution from a more
concentrated solution in a process called dilution. Water is added to a concentrated
solution to make a larger more dilute volume of solution. The concentration of the new
solution can be expressed in Percent (%) Concentration or Molarity (M).
The amount of solute doesn’t change when you make a dilution and thus the solute in the
concentrated solution = amount of solute in the diluted solution.
We can express this idea algebraically with the following equation. Using this equation
we can determine the percent concentration or Molarity of any solution with a known.
We use the letter ‘C’ or ‘%’ sign for the variable letter when determining a percent
concentration of a solution. Percent concentration is mass/volume of solute.
C1V1 = C2V2 where, C1 = initial concentration
V1 = initial volume (ml)
C2 = final concentration
V2 = final volume (ml)
We use the letter ‘M’ for the variable letter when determining Molarity of a solution.
M1V1 = M2V2 where, M1 = initial concentration
V1 = initial volume (ml)
M2 = final concentration
V2 = final volume (ml)
Both equations are used and manipulated mathematically in the same way.
Rev5Aug2014
Practice Calculations for Dilutions using Percent Concentration
When working in the biology lab your instructor asks you to prepare the following
concentrations of hydrogen peroxide (H2O2) for an upcoming lab experiment. The
concentrated hydrogen peroxide is a 3% solution. Each dilution requires a final volume
of 15 ml.
Show all calculations for each dilution you will perform.
Dilutions you need to prepare:
0.3% hydrogen peroxide
0.8% hydrogen peroxide
1.5% hydrogen peroxide
Calculations:
Practice Calculations for Dilutions using Molarity
When working in the chemistry lab your instructor asks you to prepare the following
dilute solutions from an initial concentrated stock solution of 0.01 M phenol red. Each
dilution requires a final volume of 10 ml.
Dilutions you need to prepare: 0.0001 M, 0.0003 M and 0.0005 M phenol red.
Calculations:
Rev5Aug2014