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Dilutions and Concentration of Solutions study guide and practice problems answer key
1. If you take 2.5 mL of 5 mg/mL glucose and add 7.5 mL of water, what is the concentration of the resulting diluted glucose solution ?
The dilution made is: 2.5 mL
10 mL
The concentration of the diluted glucose is:
¼ (5 mg/mL) = 1.25 mg/mL glucose
= 1/4
2. If you pipet 10 mL of 100 mM Tris buffer into a graduated cylinder, and bring the total volume of the solution to 150 mL with water, what is the final concentration of the diluted Tris solution ?
The dilution made is: 10 mL
150 mL
= 1/15
The concentration of the diluted Tris is:
(1/15) (100 mM Tris) = 6.7 mM Tris
3. You have a student helper who made a 20% glycerol solution using the following recipe:
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30 mL glycerol stock solution
60 mL water
What is the concentration of the student helper used? glycerol stock solution that the
The dilution made is: 30 mL
90 mL
The concentration of the concentrated glycerol stock:
(3/1) (20% glycerol) = 60% glycerol
= 1/3

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4. You are working in the lab on a test to determine the protein concentration in a given sample (called “A”). You take 50  L of protein sample A and add 950  L of buffer to the sample. You then run your experiment on the diluted protein, and get a concentration of
0.1 mg/mL. What is the concentration of protein in the original protein sample A ?
The dilution made is: 50  L
1000  L
= 1/20
The concentration of the original protein sample A:
(20/1) (0.1 mg/mL) = 2 mg/mL protein