How much water will be added to 20ml of alcohol to make it 20% alcohol solution?

Question

It is a question o class 9 chemistry CH 2 

 

Answer 1

That depends on what the original alcohol solution is.  Assuming it is 100% alcohol (and this is not really possible because alcohol absorbs water very rapidly), then ...

(20 ml)(100%) = (x ml)(20%)

x = 100 mls

Thus, you would have to add 80 ml of water to the 20 ml of 100% alcohol.  This also assumes that the volumes are additive, which they usually aren't.  

 

If the original alcohol is, say, 95% (much more likely in real life), then ...

(20 ml)(95%) = (x ml)(20%)

x = 95 ml

Thus, you would have to add 75 ml of water (95 ml - 20 ml).