When performing a gram stain, it is necessary to remove crystal violet stain from any gram negative bacteria on the slide. Microbiologists use a decolorizing solution to accomplish this. A common recipe is equal parts 95% ethanol and acetone. How many mL of water would you need to add if you have 99% ethanol and want to end up with 500 mL of decolorizer

10.11 mL

Explanation:

Given that :

Total volume of decolorizer = 500 mL

A common recipe is equal parts 95% ethanol and acetone.

So;

The volume of 95% ethanol in the decolorizer = 500mL/2 = 250 mL

Let represent V(ml) for the 99% of ethanol needed to make 95% of the 250 mL of ethanol;

Therefore:

V(ml) × 0.99 = 250 × 0.95

V(ml) × 0.99 = 237.5

V(ml)  = 237.5/0.99

V(ml) = 239.89 mL

Hence; the amount of water to be added to 95% of ethanol = ( 250 -  239.89 )mL = 10.11 mL