How many mL of water should be added to 2500mL of 83% (v/v)alcohol to prepare 50% (v/v) alcohol?
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Reply (by Keith)
Although you technically could use an alligation grid to work this problem, it would be a disaster and probably take up a whole sheet of paper. Alligations are best used when you have a higher and lower concentration and know what your desired volume is, which is what's missing here.
So, a better way to do this is with basic algebra, using the formula C1V1=C2V2. You can do this one in about 6 lines on paper. Here's your first line:
(2500)(.83) + (X)(.00) = (2500+X)(.50)
Solve for X
If you can spare 12 minutes,
watch this brief tutorial
I posted to YouTube
on Basic Algebra.