3: Dilutions
Students perform single-step dilution calculations using c1V1 = c2V2, determine aliquot and diluent volumes from stock and desired concentrations, and calculate dilution factors and concentration factors.
Aliquot Volumes for Dilutions
Click to show Aliquot Volumes for Dilutions example problem
You are preparing 104.0 mL with dilution factor DF=40.
What volume of aliquot in milliliters (mL) do you add to distilled water to make the dilution?
Note: answers need to be within 35% of the correct number to be correct.
Dilution Factors for Solutions
Click to show Dilution Factors for Solutions example problem
You are preparing a new solution.
You dilute 3.5 mL stock solution into 227.5 mL distilled water to make a dilution.
What is the dilution factor?
Note: answers need to be within 2% of the correct number to be correct.
Diluent Volumes for Dilutions
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You are preparing 190.0 mL with dilution factor DF=20.
What volume of diluent in milliliters (mL) do you add to the aliquoted sample?
Note: answers need to be within 1% of the correct number to be correct.
Dilution Factors
Click to show Dilution Factors example problem
Dilution factors are used in biology labs to make solutions at precise concentrations, ensure consistency across experiments, and preserve valuable samples while still meeting volume requirements. For example, if a student needs 400 mL of a working solution, it is much easier to measure a small aliquot from a concentrated stock and add water to reach the final volume than to prepare the solution from scratch each time.
You are preparing a new solution with a dilution factor of DF=26.
How much liquid do you add to make a total of 182.0 mL?
Aliquot Volumes from Stock Solutions
Click to show Aliquot Volumes from Stock Solutions example problem
| Potassium chloride (KCl) | |
| Final volume | 560 mL |
| Target concentration | 15% |
| Stock concentration | 40% |
| Molecular weight | 74.55 g/mol |
| Aliquot unit | milliliters (mL) |
You have an already prepared stock solution of 40% KCl on the shelf.
Prepare 560 mL of 15% KCl solution using the stock solution.
What volume of aliquot in milliliters (mL) do you add to distilled water to make the final dilution?
Note: answers need to be within 1% of the correct number to be correct.