Question

You need to make 350mls of a 70% ethanol solution of EtOH from a 95% solution. How would you do this?

Answer 1

Assume the 95 percent solution is made of 20 parts, one of which is water. The 70 percent will have six parts water. So add five parts water to the 95 percent, and you have it.

So you have 20 parts + 5 parts=350ml
25 parts= 350ml
1 part= 350/25 ml

So take five parts (5*350/25 ml) water, and the remaining 95 percent EtOH to the 350ml mark. If you don't have a mark,then add 350- 5*350/25 ml of EtOH.

check my thinking.