15. Dr. Haffrey told his student Amanette, to make 400 ml of a 2M concentration
ID: 201616 • Letter: 1
Question
15. Dr. Haffrey told his student Amanette, to make 400 ml of a 2M concentration of NaCI. Amanette did not want to calculate how much salt was needed by using the molecular weight of the substance Instead, she searched the laboratory for a concentrated solution and found Zachary's 5M stock solution of NaCI. a) How much of the 5M stock solution did Amanette use? Show your work (5 points) b) How much of the diluent did Amanette use? (5 points) c) What was the diluent that Amanette used? (2 points) 16.Amanette and Jason were arguing which solution had more potassium. Amanette argued that 25 mL of a 30% solution had more than 8 ml of 50% solution. jason disagreed. a) Who is correct? (2 points) b) lustify your answed below. (5 point) 17.Jason had to calculate the dilution factor in order to plate serial dilutions his concentrated cells as the correctly plating volume. He wanted his experiment to be consistent with his previous results. He saw that his starting concentration was 10 million cells/ml. The volume of the he use before dilution was 1 mL and the volume that he used after the dilution was 20, a) What is the dilution factor he used? Show your work (5 points) 18. Reneè was asked by a colleague to calculate the dilution factor of an antibiotic that was used for their bacterial culture. The antibiotic stock was 10 mg/mL which was used at a 50 g/mL a) What is the dilution factor? (5 points) w much of the stock solution does Reneè need to add to a 250 ml culture? Show your work (5 points) b) HowExplanation / Answer
AS PER CHEGG POLICY, PROCEEDING TO ANSWER ONLY THE FIRST 5 QUESTIONS/SUBPARTS, THAT IS, QUESTIONS 15 a) TO 16 b):
ANSWER 15.
Answer a)
A 5M stock contains 5 moles of NaCl per litre of stock solution. Since we only need 400 ml of a 2M solution, we will be needing ( 400 ml / 1 litre ) * 2M = 0.8 moles of NaCl in our solution.
If 5 moles are contained in 1 litre of stock, then:
0.8 moles are contained in (1/5)*0.8 litres of stock = 160 mL of stock
Hence, Amanette used 160 mL of stock NaCl solution ANSWER
Answer b)
To obtain a final volume of 400 mL, Amanette must add 400-160 = 240 mL of diluent. ANSWER
Answer c)
The diluent that Amanette used would be water (H2O) ANSWER
ANSWER 16.
Answer a) & b)
A 30% potassium solution of 25 ml Volume contains (30/100)*25 = 7.5 ml of Potassium
A 50% potassium solution of 8 ml Volume contains (50/100)*8 = 4 ml of Potassium
Amanette is correct ANSWER
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