Assignment 15 Dilution Quiz PDF

Preview

Summary

Dilution Quiz...

Description

Name Section Group# Activity Total points Grade

Answer key

A15 12

Questions (1-20) 1. The molecular weight (MW) of oxalic acid is 126.064 g/mol. How many g/L is there in a 6 M oxalic acid (C2H2O4.2H2O) solution? (0.5 pts) Answer: 756.38 g/L 2. How many ng/ml is in a solution that contains 89 g/L? (0.5 pts) Answer: 89,000,000 ng/ml 3. How many mg/ml is in a 6.9% NaOH? (0.5 pts) Answer: 69 mg/ml 4. The molecular weight of NaCl is 58.44. How many mg/ml is there in a 2 mM NaCl solution? (0.5 pts) Answer: 0.12 mg/ml 5. How many mL of 15 M H2SO4 are required to prepare 500 mL of 3 M H2SO4? (0.5 pts) Answer: 100 ml of 15 M H2SO4 6. How can you make a 18% NaOH solution? (0.5 pts) Answer: 18 g NaOH is brought up in 100 ml H2O. A wrong answer is simply adding 18 g to 100 ml

Commented [BN1]: Many answers possible

7. Make a 6 M solution in 1 L using a compound with a molecular weight of 75 g/mol. (a) How many grams of the solute should you weight out? (b) How would you suspend the mixture? (1 pt) Answer: (a) Weigh out 450 g and (b) bring the volume to 1L with solvent. Incorrect answer: add 450 g to 1 L. 8. Izabel needs 1.2 L of 10% NaOH solution for preparing a lab reagent. She has a 12% NaOH stock solution in her lab. Which of the following mixtures will yield the volume and strength needed to fill this order? (0.5 pts) A. 800 ml of 12% NaOH and 400 ml of sterilized water B. 1000 ml of sterilized water and 200 ml of 12% NaOH C. 600 ml of 12% NaOH and 600 ml of sterilized water D. 200 ml of sterilized water and 1000 ml of 12% NaOH Answer: D 9. Katie’s experiment requires 250 ml solution of 10 mM Tris-HCl, 25 mM NaCl. She has a 2 M Tris-HCl solution available and plenty of solid NaCl (MW = 58.44 g/mol). Help her prepare the mixture. (0.5 pts) A. Add 0.36 g NaCl, add 1.25 ml 2 M Tris-HCl and bring volume to 250 ml with water B. Add 0.0036 g NaCl, add 1.025 ml 2 M Tris-HCl, and bring volume to 250 ml with water C. Add 0.036 g NaCl, add 1 ml 2 M Tris-HCl, and bring volume to 250 ml with water 1

D. Add 3.6 g NaCl, add 1 ml 2 M Tris-HCl, and bring volume to 250 ml with water E. None of the above Answer: A 10. Katie’s experiment requires 250 ml solution of 10 mM Tris-HCl, 25 mM NaCl. She has a 2 M Tris-HCl solution available and plenty of solid NaCl (MW = 58.44 g/mol). Help her prepare the mixture. (0.5 pts) A. Add 0.36 g NaCl, add 1.25 ml 2 M Tris-HCl and add 250 ml water B. Add 0.0036 g NaCl, add 1.025 ml 2 M Tris-HCl, and add 250 ml water C. Add 0.036 g NaCl, add 1 ml 2 M Tris-HCl, and add 250 ml water D. Add 3.6 g NaCl, add 1 ml 2 M Tris-HCl, and add 250 ml water E. None of the above Answer: E A would be correct based on calculation, but Katie did not bring the solution up in water, instead she added 250 ml water. Because of this error, her concentrations are wrong. 11. Now, Katie’s experiment requires 1 ml of 1 mM Tris-HCl, 25 uM NaCl. The lab technician has 1M Tris-HCl and solid NaCl (MW = 58.44 g/mol). When she went to measure the NaCl, she saw the weight machine in the lab cannot measure below 10 ug and the lowest measurement in micropipette available in the lab is 10 ul. What problem Katie faced to make this solution? Describe a possible solution. (0.5 pts) Answer: She needs 1.46 ug NaCl and 1 ul Tris-HCl to make reagent B, which she cannot measure. She can make higher amount like 10 ml reagent B and make 1 ml aliquots.

Commented [BN2]: Many possible answers

12. A new strain E. coli has infected over 1,000 cattle in North Dakota and the infection is spreading. Zabel has determined that this bacterium is sensitive to ampicillin, a common antibiotic, and the MIC (minimum inhibitory concentration) is 200 ug/ml. Zabel has 10 frozen aliquots of 1 ml of 100 mg/ml ampicillin stock solution. She will only thaw what she needs for an experiment, because after thawing the excess antibiotic will be discarded, she has limited supply, and the antibiotic is expensive. She has isolated 6 ml of blood from an infected cow in South Dakota, just across the border from the infect site in North Dakota. She has determined that the SD cow is infected with an E. coli strain, but she does not know if it is the same strain infecting the cattle in ND. She will test if the ampicillin would be effective in killing the E. coli in the SD cow. How many aliquots of ampicillin stock should she thaw and what is the minimal ul she should use on the 6 ml E. coli culture to test if this would be an effective treatment for the SD infected cow? (0.5 pts) A. 2 aliquots and 0.12 ul needed B. 1 aliquot and 0.102 ul needed C. 1 aliquot and 12 ul needed D. 1 aliquot and 120 ul needed E. None of the above Answer: C

Commented [BN3]: Too complex for an exam.

13. Mark diluted 5 ml of MMB media into 195 ml sterile water. How many times did he diluted the solution? (0.5 pts) A. 30 times B. 40 times C. 5 times D. 195 times E. 200 times Answer: B 2

14. Mark has 7 ml of an E. coli starter culture. He needs to know how many bacteria are in his culture, so he diluted the culture following way: (0.5 pts) Dilution tube 1: 50 ul culture and 950 ul H2O, mixed well and 100 ul plated Dilution tube 2: 40 ul culture from tube 1 and 160 ul H2O, mixed well and 100 ul plated Dilution tube 3: 50 ul culture from tube 2 and 50 ul H2O, mixed well and 100 ul plated The next day, he counted colonies. He counted 500 colonies on plate 3, 1050 colonies on plate 2, and there were too many to count on plate 1. What is approximate number of bacteria in the starter culture? A. 70,000,000 bacteria B. 1,050,000 bacteria C. 1,000,000 bacteria D. 100,000,000,000 bacteria E. 7,000,000 bacteria F. B and C Answer: E 15. Ahana brought up 10 g sawdust in 10 ml sterile water and plated 100 ul of different dilutions. The next day she counted colonies and there were 96 different colonies in the 1:500 dilution she plated. She grouped the colonies according to their color. She counted 16 red colonies, 50 colorless colonies, and 30 yellow colonies. What would be the approximate CFU/g yellow bacteria in the saw dust? (0.5 pts) Answer: 150,000 CFU/g

Commented [BN4]: Too complex for an exam.

16. Mark isolated 10 g soil from the SDSU central field and brought it up in 10 ml sterile 20% ethanol (because he wants ethanol stress tolerant bacteria), and then he diluted the culture serially in 20% ethanol 1:10 (tube 1), 1:10 (tube 2), 1:10 (tube 3), 1:10 (tube 4), and 1:10 (tube 5). He plated 100 ul of each serial dilution and incubated the plates overnight at 37 qC. He counted 296 colonies on plate 4, and 29 colonies on plate 5. What should be the conclusion from his result? (0.5 pts) A. The culture has ~2,900 CFU/ml B. The culture has ~2.9E+04 CFU/ml C. The culture has ~2,900,000 CFU/ml D. The culture has ~2.9E+07 CFU/ml E. The culture has ~2.9E+08 CFU/ml Answer: D

Commented [BN5]: Too complex for an exam.

3

17. Rori had a 5 ml E.coli culture, which she diluted in two different solvents: sterile 0.1% NaCl (Set 1) and sterile H2O (Set 2). She did the following dilutions and grew Petri plates with rich media overnight:

Commented [BN6]: Q17-18: Too complex for an exam.

Set 1: 0.1% NaCl Set 2: H2O Mix 1: 100 ul of culture into 900 ul 0.1% Mix A: 64 ul of culture into 896 ul H2O mix NaCl, mix well, and plate 50 ul on plate 1 well, and plate 50 ul on plate A Mix 2: 10 ul Mix 1 into 990 ul 0.1% NaCl, mix Mix : 50 ul Mix A into 450 ul H2O, mix well, and plate 50 ul on plate 2 well, and plate 50 ul on plate B Mix 3: 5 ul Mix 2 into 195 ul 0.1% NaCl, mix Mix C: 7 ul Mix B into 273 ul H2O, mix well, and plate 50 ul on plate 3 well, and plate 50 ul on plate C Mix 4: 0.1 ml Mix 3 into 0.9 ml 0.1% NaCl, Mix D: 10 ul Mix C into 990 ul H2O, mix mix well, and plate 50 ul on plate 4 well, and plate 50 ul on plate D Mix 5: 60 ul Mix 4 into 840 ul 0.1% NaCl, mix Mix E: 20 ul Mix D into 180 ul H2O, mix well, and plate 50 ul on plate 5 well, and plate 50 ul on plate E In the first set of plates (Set 1), she counted 45 colonies on plate 5, 675 colonies on plate 4, and she did not count the other plates. In the second set of plate (Set 2), she counted 39 colonies on plate E, and she did not count the other plates. Predict the approximate colony number that should be on plate D for Set 2. (0.5 pts) Answer: approximately 390 colonies (10*39) 18. Use the information from question 17. (a) Calculate the CFU/ml for Set 1 and Set 2 based on counts from plates 1-5 and plates A-E, respectively. You will calculate that Set 1 has more CFU/ml that Set 2. (b) Justify this, and assume that Rori made no mistakes in her dilutions, mixing, or plating (assume no errors on Rori’s part). (1 pt) Answer: a. Set 1: 5.4×10^9 CFU/ml; Set 2: 4.6×10^9 CFU/ml b. Set 1used 0.85% NaCl, which may play role in bacterial growth. Dilutions: Set 1: 1:10, 1:100, 1:40, 1:10, 1:15 Set 2: 1:15, 1:10, 1:40, 1:100, 1:10 Total dilution in both case: 1:6000000 19. Saline is used as a base for many medications (e.g. used for dehydration and drug delivery) and products (e.g. contact lens fluid) used in human health. Saline is a 0.9% solution of NaCl (MW: 58.44). To make a 1 L saline solution, how many grams should you dissolve into water (sterilize after dissolving)? (0.5 pts) A. 0.9 g B. 9 g C. 90 g D. 0.9 mg E. 0.9 ug Answer: B 20. Use the information from question 19. What is the molarity of saline? (0.5 pts) A. 154 M B. 1540 mM C. 1,540 mM D.154,000 uM E. 15,400 nM Answer: D 4

Copy protected with Online-PDF-No-Copy.com...