# Molarity given percent solution and density.

## Homework Statement

Lactose (C12H22O11; MM=342) is a sugar found in mamalian milk. The density of a 12.0% solution is approximately 1.06 g/mL. What is the molarity, molality, and mole fraction of the solution?

## Homework Equations

M=g/L, m=mol/kg, molefraction=mol/mol??

## The Attempt at a Solution

I think I can get this one if I can just determine the molarity. I definitely did something wrong.

M=mol/L
1.06 / 1000 = .00106; .00106/342 = 3.099x10^-6M
I figured since I know g/mL as well as mol/g, I can divide to get mol/mL, then convert to get L. Apparently this is not the case?

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You're on the right track, just a few things you need to pay attention to:

1.06 grams of solution contains how many grams of lactose?

Also, show your units at all steps of the calculation to make sure you're converting correctly.

Last edited:
Borek
Mentor
Last edited:
Hmm, then let me try this again. I just want to find the moles of Lactose for now, then I think I got the rest.

1.06 g/mL * 1mol/342g * 12% lactose = 3.719x10^-4

Does that look right?

Thanks for the help btw.

That looks good, but remember to keep track of the units.

Borek
Mentor
I just want to find the moles of Lactose for now
Moles of lactose in what?

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