Question

1. What is the molar concentration of sucrose in a can of Red Bull (27 g sucrose/250 mL)?

2. How much glycine is needed to make 125 mL of a 1.5 M stock solution?

3. What volume of ethylene glycol is needed to prepare 200 mL of a 0.25 M stock solution?

4. Using the above stock solutions from questions #2 and #3, how would you prepare 750 mL of a solution that is 10 mM in glycine and 25 mM in ethylene glycol?

5. You are given a stock solution of 50 mM of alkaline phosphatase. What volume of this solution would you need to add to what volume of distilled water to make 25 mL of a 5 mM solution?

6. You are given a 50X stock solution of DNA gel running buffer and asked to make 25 mL of the corresponding 1X solution. What volumes of the stock solution and water do you need?

7. You are given a 0.5 M solution of sodium citrate. How would you make 3 mL of a 20-fold dilution?

8. Consider an assay that involves a serial dilution as listed below. What is the total dilution factor for this assay?

--0.5 mL of trypsin is pipetted into 1.0 mL of buffer.

--0.035 mL of this sample is then pipetted into 1.0 mL of the assay solution.

9. You are given 1.0 mL of the enzyme amylase and add cold 95% ethanol to reach a final concentration of 25% ethanol. What volume of the 95% ethanol did you need to add to the enzyme solution to obtain this concentration?
(*note: this one is a little tricky—you will need to account for the starting volume of the enzyme solution.)

10. Do the following conversions. (Show all work)

a. 0.5 mg/mL to μg/uL
b. 0.2g to ug
c. 0.4 μM to mmol/mL

Answer 1

1. What is the molar concentration of sucrose in a can of Red Bull (27 g sucrose/250 mL)?

mass of sucrose = 27 g

molar mass sucrose = 342 g / mol

moles of sucrose = mass / molar mass

                          = 27 / 342

                          = 0.0789

volume = 250 mL = 0.250 L

molarity = moles / volume

             = 0.0789 / 0.250

            = 0.316 M

2.) How much glycine is needed to make 125 mL of a 1.5 M stock solution?

moles of glycine = volume x molarity

                         = 0.125 x 1.5

                        = 0.1875

molar mass of glycine = 75 g / mol

mass of glycine = moles x molar mass

                       = 0.1875 x 75

                     = 14.1 g

mass of glycine = 14.1 g