Question

1. How would you prepare 50ml solution of 7% v/v from 20% v/v stock solution? 2. Can you prepare a 12% v/v solution from a 2% v/v solution? why or why not?

Answer 1

to prepare 20% v/v solution we have to take 20ml and make upto 100 ml with solvent

so it indicates each ml consists of 0.2 mL of solute

to prepare 7% solution normally we have to take 7 mL and make up to 100 mL

from 20% solution the each 1 mL consists of 0.2 mL of solute so 10 mL consists of 2 mL solute so we need 7 mL so we have to take 35 mL and make upto 100 to produce 7% solution

where as we have to produce only 50mL so 35/2= 17.5 mL from the stock solution and make up to 50 mL to produce 7% solution

2) 12% solution has to be prepared by dissolving 12 mL of solute in 100 mL of solvent but in 2 % solution 2 mL solute in 100mL solvent so it is not preffered to prepare in from low to high concentration solutions

but we can done it by taking 1200 mL of 2% solution and evaoporate to 100 mL so then also we can get 12% v/v solution but it is not preferred method in this case