# Checking my answer/approach - specific gravity of a mixture

1. Dec 1, 2012

### Cloud 9

1. The problem statement, all variables and given/known data
What is the specific gravity of a mixture 40% ethyl alcohol and 60% water? The specific gravity of ethyl alcohol is 0.79.

2. Relevant equations

3. The attempt at a solution
He showed us a way to do it for another type of problem but I approached it a bit differently and I wanted to make sure my answer was logical/correct before submitting it. So what I did was this:

Assume 100 mL of mixture. Then you have 40 mL alcohol, 60 mL water.
Density of water = 1 = mass/60 mL; mass of water therefore = 60 g
0.79 = density of alcohol/density of water (1), so density of alcohol = 0.79
I set up a cross multiplication:

0.79 g/1 mL = x g/40 mL
I got 31.6 g of ethyl alcohol.

So the total mass of the mixture is 91.6 g.

Thus the density of the mixture is 91.6 g/100 mL = 0.916

Thus specific gravity of the mixture = 0.916/1 = 0.916.

Does this seem accurate?

2. Dec 2, 2012

### haruspex

Yes, that's right, if the 60% and 40% were by volume.