How can you determine the mass, volume, or moles?

Nov 2016
3
0
Merced, CA
I had a quiz today, and had no idea what the instructor expected us to do based off the information given. I'm trying to figure out how we were supposed to get the mass, volume, or moles to help solve the problems.
I don't want any answers, just advice on how to use the information to get me to the answers.

The information given:
Glucose in a sucrose solution with 2.3 m and a density of 1.12 g/mL.
She provided the molar mass for glucose. (180.18 g/mole)

The information required:
Mass of solution, solute, solvent
Moles of solute, solvent
Volume of solution, solute, solvent

I have absolutely no clue as to how we are supposed to get all that. I assumed the solvent is water, so I can determine the density of glucose in the solution. She didn't provide us any volume, mass, or moles.

Does anyone have any tips for this? I'm not the only student who didn't know what to do for this. I know it's got to be something really obvious, she was already grading quizzes when we turned them in so nothing was left out.
 
Last edited:
Nov 2016
4
1
Nowhere
Resolution

Hi, don't worry about it its fairly simple you'll get it immediately, so they give you molality, which is 2.3 mols of solute/Kg of solvent, the density of the solution (1.12g/ml) and the molar mass of the solute which is 180.18g/mol.

Ok, first off, as they don't give you a specific quantity of the solution ,but instead, different concentrations of it, we're going to assume that there are 1000g of solvent and 2.3 mols of solute, as indicated in the molaity, from this point you ca nuse the molar mass to calculate the amount of grams of the solute from its mols (2.3), afterwards just add solvent and solute and you'll obtain the total mass of the solution.

For the second step you already have the mols of the solute and the mass of the solvent, so from this mass you can calculate the mols of water from its molar mass (18g/mol), add the two of them and you'll have the total amount of mols for the solution.

Finally with the density you just have to divide each mass with the density and you'll obtain the amount of volume of each one of them.
 
Nov 2016
3
0
Merced, CA
Yeah, I was over-thinking it too much. I actually spoke to another professor this morning, and he couldn't see the connection, either. When my professor had her office hour, she pointed that part out. Not sure what I was assuming in trying to complicate the whole molality. I was trying to do something where you have two unknowns that equal the 2.3. Well, simply she said it's the 1000 g and 2.3 moles.
I also think the sucrose part was confusing for some. Sucrose is different, so that is what confused some.