Chemistry Forum

Hi there!

I'm having trouble calculating the molar concentration of 70% isopropanol (2-propanol). Said 70% is by weight. I'd really appreciate some help since i don't know how to calculate this.

Are you sure its by weight. Alcohol is normaly calculated by volume. Nevertheless weight means 1 kg contain 700 g Isopropanol = 70 % w.w.
If it is by volume its 700 ml in 1 l alcohol = 70% v.v.
To convert you need the specific gravity.

Yeah, im sorry, i made a mistake. The actual concentration is 99.7% v-v, and the density is 0.786 g/cm3.

So 1 l has a weight of 786 g, 99,7% v.v is 997 ml 100% alcohol. 3 ml = 3 g is water.. So the concentration is (786 g -3 g) / 0,997 l = 785,36 g/ l. The molar mass is 60 g/mol what gives a molarity of 13,08 mol/l.

Thank you very much! That helps a lot.