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5 Jan 2018

A. You want to make 500 ml of 1M NaCl (FW = 58.44). What mass of NaCl do you use? Show your work.

29.22 g NaCl / 500 ml

B. Now outline how you will perform a serial dilution comprised of 5 steps with a dilution factor of 2 at each step. What is the salt concentration at each step?

Need help with B only!

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Jean Keeling
Jean KeelingLv2
7 Jan 2018
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Related questions

This question deals with dilutions. It has four parts.

A) If the dilution of a sample is 1/8, what is the dilution factor (D.F.)? I got my answer to be 8.

B) Suppose you want to make a 1/18 dilution of a sample.
If you use 7 ml of the sample, how many ml of diluent do you need to use?
(NOTE: You do not need to put units in your answer, the units in this problem are milliliters.) I got my answer to be 119.

C) In a three step serial dilution:
the first dilution is 1/6
the second dilution is 1/2
the third dilution is 1/10

What is the total dilution factor of this three step serial dilution procedure?
(HINT: Remember that D.F. = 1/dil. Also remember that the term for D.F has no units.) I got my answer to be 720.

D) To determine the concentration of bacteria in a liquid sample, you prepare a serial dilution of the culture and spread 0.10 ml aliquots of several of the dilutions on plates of a rich agar medium.
After incubating, you see 200 colonies on the spread plate that was prepared from the 10-2 dilution.
What was the concentration of viable bacteria in the liquid culture?
(Units for the answer to this problem are CFU/ml but do not enter the units in your response.) I got my answer to be 2e5.

Can someone please check these for me? This is online homework, and I have to submit everything at the same time, so if I get one wrong, the entire problem is wrong!

Please answer all the questions answering only one question is not helpful :

Calculations on Multiple Stock Solutions—be sure to include the amount of water added and include all units

11. Calculate how to use the 1 M Tris and 0.2 M EDTA stock solutions to make the 400 ml of a of 10 mM Tris and 1 mM EDTA solution.

12. Calculate how to use a 3 M NaCl and 10% NP40 stock solutions to make a 500 ml of a 300 mM NaCl and a 0.2% NP40 working solution.

Calculations on Simple Dilutions—be sure to include the amount of water added and include all units

13. Calculate the volumes necessary to make 200 ml of a 1:5 dilution of a sample.

14. Calculate the volumes necessary to make 50 ml of a 1:8 dilution of a sample

15. Calculate how you would dilute a cell suspension containing 3,000,000 cells/ml to obtain 10 ml with 100,000 cells/ml

16. Calculate the volume of a cell suspension containing 800,000 cells/ml you would need to obtain a total of 250,000 cells

Practice Calculations on Serial Dilutions—be sure to include the amount of water added and include all units

17. Calculate and describe (or diagram) how you would use a 10% SDS solution to prepare a final volume of 20 ml of each of the following solutions: 8%, 4%, 2%, 1% 0.5%.

18. Calculate and describe (or diagram) how you would use a 5 M Tris solution to prepare 200 ml of each of the following solutions: 1M, 100 mM ,10 mM , 1 mM, 0.1 mM.

How much of the first dilution should you make to perform the following dilutions?

19. 300 ml of a 1:5 dilution

20. 100 ml of a 1:10 dilution

21. What is the minimum volume you should pipette with the following? (include units with your answers):

P2 P10 P20 P100 P200 P1000

22. How accurate was your pipetting?

23. Was it better with the larger volume or smaller volume pipettor? Provide rationale.

(If there was a consistent problem with one pipettor please tell the instructor.)

Standard Curves

24. Complete a standard curve for the data above and tape a printed version into your notebook.

25. What is the R-squared value of your trend line? Is this good or bad… i.e. would you repeat the assay?

26. What is the protein concentration of (Explain/show your calculations.)

Unknown #1 = Unknown #2 =

Data for DNA Concentration Procedure

Attach a labeled printout of the plate reader raw data as well as your generated standard curve to this lab.

26. What is the concentration of your unknown DNA sample?

27. What is the R 2 for your standard curve data? Why is it important that the R2 is >0.95?

28. Comment on the purity of your DNA... discuss- How can you determine the purity of DNA? What are common contaminants of DNA purified from cells?

You ask your lab assistant to prepare 1L of solution Zeta at a concentration of 1 M. He comes up to you with a 0.5 M stock solution and asks for help in calculating how much to use. What do you tell him?

2. Illustrate, as on your first lab calculation handout, how you would make 3 serial 4-fold dilutions of an original stock solution. Indicate for each tube (you can set up a table beneath the diagram), including the original stock solution, the following information:

A. What is the n-fold dilution for each tube ?

B. What is the relative concentration for each tube ?

C. What is the actual concentration in each tube if the original concentration = 1 M ?

D. If the original tube has 400 cells per mL, how many cells per mL are in each dilution tube ?

E. If you pipetted 0.25 mL of the second dilution tube into a cuvette, how many cells would there be in the cuvette ?

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