2) How much of a 70% ethanol solution is required for dilution to make 700ml of a 20% solution?
Question from student: Im stuck, I dont know how to go about this please show me a quick and easy way to approach questions like this!
Answer from tutor: 20% solution contains 20g in 100ml, so in 700 ml there is 140g of ethanol. The next stage is to work out how much of the 70% solution do you need to get 140g. Well 70% is 70g in 100ml. So you need 200ml.
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