1). One of the solutions used to make bacterial cells competent is CaCl 2 (molar

Question

1). One of the solutions used to make bacterial cells competent is CaCl2 (molar mass = 110.98 g/mol). Your lab instructor will perform this task for you prior to the start of lab. However, you need to double-check your lab instructors’ calculations to ensure that the CaCl2 solution used to make your bacterial is the correct concentration. You lab instructor plans to make a 1M CaCl2 stock solution, that he or she will then dilute to a final working concentration of 350mM.

a.) Your Lab Instructor has determined that 27.75g is required to make 250mL of 1M CaCl2. Is this correct? Show all of your work for full credit.

b.) Your Lab Instructor has calculated that a 355mL of 1M CaCl2 is required to make a 350mM CaCl2 solution in 875mL total volume. Is this correct? Show all of your work for full credit.

Explanation / Answer

CaCl2 is 111 g / mol

A. To make 250 ml of 1M solution

M= n / V

1 = n / 0.25

n = 0.25 mole

0.25 mole or 27.75 g of calcium chloride is required. So the instructor is correct

B. 355ml of 1M CaCl2 will have 0.355 moles of it or 39.4 g

350mM in 875 ml will have

350× 10 -3 = n/ 0.875

n = 0.306 moles or 33.99 g

So this calculation of lab instructor is incorrect as he has used more volume of the solution.

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