1 Your lab partner made three 20 mL volumes of penicillin at

1) Your lab partner made three 20 mL volumes of penicillin at the following concentrations: 15 mg/mL, 18 mg/mL, and 45 mg/mL. Your lab protocol requires a large amount of 25 mg/mL penicillin, so you decide to combine all of the three solutions to make as much at that concentration as possible. How much 25 mg/mL penicillin can you make? How much water will you need to add?

2) You started with a cell count of 6.5 x 10⁵ cells / ml in a total volume of 5ml. You need to seed a six-well plate with the following numbers. Calculate the volume of cell suspension you will need to transfer into 1 well. Each letter represents a different scenario.

a) 1.5 x 10⁴ cells/mL and up to 2 mL / well

b) 2.5 x 10⁵cells/well and up to 2 mL / well

c) 3 x 10⁵cells/well and up to 2 mL / well

Solution

Answer:

15 mg/mL= 20 mL x 15 mg =300 mg

18 mg/mL= 20 mL x 18 mg = 360 mg

45 mg/mL = 20 mL x 45 mg =900 mg

Total penicillin = 1560 mg

Total volume = 60 mL

So = 1560 mg/60 mL = 26 mg/mL

Stock = 26 mg/mL

Required = 25 mg/mL

Stock Volume = 60 mL

C1V1= C2V2

(stock)   (required)

V2=C2V1/C1

V1 = ( 25mg/mL X 60 mL )/ 26 mg/mL

= 57.7 mL

57.7 mL of stock + 2.3 mL of H2O gives 60 mL of 25mg/mLof Penicillin.