Question

a pharmacist needs to strengthen a 10% alcohol solution to one of 20%alcohol. how much pure alcohol should be added to 400ml of 10% solution

Answer 1

Throughout the process the net amount of water is constant. In 20 percent alcohol solution, 80 percent is water. And in the given 400 ml solution 90 percent i.e. 360 ml is water and 40 ml is alcohol. If it is 80 percent, 20 percent is 90 ml. Since 40 ml is already there, 50 ml is to be added.