1
Chapter 13 Problem Set B Key: Dilutions and Concentration
1. How would you prepare 10 mL of a 1/10 dilution?
1 mL stock + 9 mL water
2. How would you prepare 1 mL of a 1/10 dilution?
0.1 mL stock + 0.9 mL water
3. How would you prepare 100 mL of a 1/10 dilution?
10 mL stock + 90 mL water
4. How would you prepare 25 mL of a 1/10 dilution?
2.5 mL stock + 22.5 mL water
5. How would you prepare 150 mL of a 1/250 dilution of blood?
0.6 mL of blood and bring to volume of 150 mL with buffer
6. How would you prepare 400 L of a 1/100 dilution of food coloring?
4 uL of food coloring + 396 uL of water
7. A 2 M solution of Tris buffer is diluted 1/100. What is the final
concentration of Tris?
a. Express your answer in M.
0.02 M
b. Express your answer in mM.
20 mM
8. You have a 1 M solution of phosphate buffer. You remove 1 mL of the
buffer and combine it with 9 mL of water. What is the concentration of
the diluted buffer?
0.1 M
9. You take 100 mL of bacteria and grind them into a “cell paste”. Then,
you remove 20 L of these cells and perform a test that tells you how
much protein is present. Your test shows that 6 g of protein are present
in the 20 L of cell paste. What was the concentration of protein in the
cell paste? Express your answer in units of mg/mL.
0.3 mg/mL
2
10. If you prepare a 1/10 dilution of a 10 mg/mL solution, what is the final
concentration of the solution?
1 mg/mL
11.If you prepare a 1:1 dilution of a 10 mg/mL solution, what is the final
concentration of the solution?
5 mg/mL
12. You have a 2.5 M solution of NaCl. You remove 10 L of the solution
and add 990 L of water. What is the concentration of the diluted salt
solution?
0.025 M
13. Suppose you have 20 L of an expensive enzyme and you cannot afford
to buy more. The enzyme has a concentration of 10,000 Units/mL. You
are going to do an experiment that requires tubes with a concentration of
1 Unit/mL of enzyme and each tube will have a 50 mL total volume.
a. How many units of enzyme does each tube require?
50 units
b. How many tubes can you prepare before you run out of enzyme?
4 tubes
14. In a protein assay, the amount of protein in 1 mL of diluted sample was
87 mg. If the original sample was diluted 1/50, what was the
concentration of protein in the original sample?
4,350 mg/mL
15. Suppose you do a test to determine how much protein is present in a
sample. To perform the test, it is necessary to dilute the original sample
1/100.
a. If the test shows that the concentration of protein in the diluted
sample was 5 g/mL, what was the concentration of protein in the
undiluted sample?
500 g/mL
b. How much protein was present in 100 mL of the original,
undiluted sample?
50,000 g