Question

Ethanol is commercially available as a 95% solution. For the sterilization of materials for cell culture, you will need a 70% solution. How would you make 400 ml of a 70% solution?

Answer 1

Ans. Using C1V1 (95% soln.) = C2V2 (70% soln.)

            Or, V1 = (70% x 400 mL) / 95%

            Hence, V1 = 294.74 mL

Hence, required volume of 95% ethanol soln. = 294.74 mL

Preparation: Taken 294.74 mL of 95% ethanol in a 400-mL standard volumetric flask. Make the final volume up to the mark with distilled water. Mix well. It’s the desired soln.- 400 mL of 70% ethanol.

Note:

I. The volume of ethanol and water is NOT additive, so don’t add 105.26 mL of distilled water to 294.74 mL 95% ethanol to make the final volume of 400 mL- the resultant volume would always be lesser than 400 mL.

II. If 400-mL standard volumetric flask is not available, make 500 mL of 75% solution (take 368.42 mL of 95% ethanol in a 500-mL standard volumetric flask, make the final volume up to the mark with distilled water- mix well to get 500 mL of 70% ethanol) and use 400.0 mL of it.

III. Or make two solution- 200 mL each in two different 200-mL standard volumetric flasks using calculations described at top. Or, use other volumetric flasks as available.