Question

What is the molality of a solution that has 80 grams of Benzoic Acid dissolved in 400 mL of ethanol. The density of ethanol is .789 grams/moles

Answer 1

moles benzoic acid = grams/molar mass.
Use density to calculate mass ethanol, then convert to kg. (By the way, that density is 0.789 g/mL and not /mol).
Then molality = moles benzoic acid/kg solvent.

Answer 2

How do i use density to calculate mass of ethanol?

Answer 3

mass = volume x density
You know 400 mL ethanol and you know the density. That will give you the mass. Use that, convert to kg and substitute into m = moles/kg solvent.

Answer 4

I get .66 moles of Benzoic for the first step which is converting the 80 grams of Benzoic into moles.


Then i did mass=volume x density
and got .3156 kg.

what do i do with those two numbers

Answer 5

First you should not round the 80/122.123 value. I get 0.65508 and I just carry those numbers in the calculator. Your other value of 0.3156 kg solvent is correct.
Now molality = moles/kg solvent.
moles = 0.65508 (which is still in my calculator) and divide by kg of 0.3156 = ??, then round to 2 places, if the value of 80 g benzoic acid is stated that way in the problem, or to 3 places if it is listed as 80.0 grams.

Answer 6

This was so helpful. Thank you for all of your patience and cooperation!

Answer 7

You're welcome. Come again.