You are told to prepare 70% v/v bottle of ethanol to spray down a laminar flow hood.

Question

You are told to prepare 70% v/v bottle of ethanol to spray down a laminar flow hood.The maximum volume on the spray bottle is 250 ml. You have a 95% v/v stock bottle bottle of ethanol. What volume in ml of the stock do you need? Round to the first decimal place.

Answer 1

Since the total volume will be 250 ml and ethanol will comprise 70%:

 

.70 x 250 = 175

 

So now calculate how much 95% solution contains 175 ml ethanol:

 

.95x = 175

x = 175/.95

x = 184.21

 

You will need 184.2 ml of the stock solution.