Answers for Laboratory Calculation Problem Set #1
1. You need to make a 1:5 dilution of a solution. You need 10 ml of the diluted solution. How much initial sample and diluent should you use?
Answer: 1:5 dilution = 1/5 dilution = 1 part sample and 4 parts diluent in a total of 5 parts. If you need 10 ml, final volume, then you need 1/5 of 10 ml = 2 ml sample. To bring this 2 ml sample up to a total volume of 10 ml, you must add 10 ml - 2 ml = 8 ml diluent.
2. How would you prepare 500 ml of a 10% NaCl solution?
Answer: In this problem, the % solution is the number of grams solute in 100 ml solvent, so a 10% solution of NaCl is 10 grams NaCl in 100 ml water. But you need 500 ml, final volume, so 10 g x 5 = 50 g NaCl.
3. If you have DNA with a concentration of 2 µg/µl, how much DNA (in µl) must be added to make a 20 µl solution with a DNA concentration of 1 µg/µl?
Answer: Since you know the initial concentration (2 µg/µl), the final concentration (1 µg/µl), and the final volume (20 µl), the following formula can be used to calculate the amount of DNA needed (initial volume)
4. You have a 10x TBE buffer. To run a gel, you need 500 ml of a 2x solution of TBE. How do you make a 500 ml solution of 2x TBE buffer from the 10x buffer?
Answer: Since you know the initial concentration (10x), the final concentration (2x), and the final volume (500 ml), you can use the formula:
Then, to calculate the amount of water needed, use the following formula:
5. You want to make a 0.5% agarose gel. How much agarose (in grams) do you need to make up a 50 ml gel solution?
Answer: There are at least two methods for solving this question (as with many dilution problems): logically and mathmatically.
6. What is the DNA concentration of a 50 µl solution which contains 10 µl of DNA at a concentration of 4 µg/µl?
Answer: There are two ways to solve this problem:
7. How would you make a 3x TBE buffer from a 12x TBE buffer for a total volume of 200 ml?
Answer: Since you know the initial concentration (12x), the final concentration (3x), and the final volume (200 ml), you can use the formula:
Then, to calculate the amount of water needed;
Thanks are given to Tim Allen and the MMG graduate students for providing these problems.
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