Question

You're asked to prepare 10mL of a PBS solution (phosphate buffer saline) containing 40% glycerol. All you have is a 10X PBS solution (10 times more concentrated than the solution you're asked to prepare). How are you going to procede in order to prepare a 1X PBS solution containing 40% glycerol?

b) What is the molarity of the glycerol in solution? (given: Density of glycerol is 1.257g/cm^3 and molar mass is 92.1g/mol)

Answer 1

To prepare a 1X PBS solution containing 40% glycerol we use following expression

C1V1 = C2V2

Here C1 = 10X and C2 = 1 X and V2 = 10 ml

C1V1 = C2V2

10X * V1 = 1X* 10ml

V1 = 1 ml

To prepare a 1X PBS solution containing 40% glycerol take 1 ml of 10X PBS solution and than make up it to 10 ml.

b) What is the molarity of the glycerol in solution? (given: Density of glycerol is 1.257g/cm^3 and molar mass is 92.1g/mol)

Given that;

40% glycerol = 40 /100 = 40 ml

1.0 ml = 1.0 cm^3 so 40 ml = 40 cm^3

Now convert it into g by density

Density = mass /volume

Mass = density * volume

Mass = 1.257g/cm^3 * 40 cm^3

Mass = 50.28 g

Now calcualte the number of moles in 50.28 g as follows:

Number of moles = 50.28 g/ 92.1g/mol = 0.55 mol

And molarity = number of volume / volume in L

Here volume = 10 ml = 0.010 L

Molarity = 0.55 mol / 0.010 L = 55 M