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 154.0 mL with dilution factor DF=35.
What volume of aliquot in milliliters (mL) do you add to distilled water to make the dilution?
Note: answers need to be within 21% 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 8.6 mL stock solution into 206.4 mL distilled water to make a dilution.
What is the dilution factor?
Note: answers need to be within 4% of the correct number to be correct.
Diluent Volumes for Dilutions
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You are preparing 51.0 mL with dilution factor DF=6.
What volume of diluent in milliliters (mL) do you add to the aliquoted sample?
Note: answers need to be within 3% 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=88.
How much liquid do you add to make a total of 396.0 mL?
Aliquot Volumes from Stock Solutions
Click to show Aliquot Volumes from Stock Solutions example problem
| Magnesium sulfate (MgSO4) | |
| Final volume | 630 μL |
| Target concentration | 80% |
| Stock concentration | 140% |
| Molecular weight | 120.37 g/mol |
| Aliquot unit | microliters (μL) |
You have an already prepared stock solution of 140% MgSO4 on the shelf.
Prepare 630 μL of 80% MgSO4 solution using the stock solution.
What volume of aliquot in microliters (μL) 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.