Molarity given percent solution and density.

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SUMMARY

The discussion focuses on calculating the molarity, molality, and mole fraction of a 12.0% lactose solution with a density of 1.06 g/mL. The correct approach involves converting the percentage concentration to molarity by first determining the mass of lactose in a given volume of solution. The participants emphasize the importance of unit conversion and tracking throughout the calculations to avoid errors. The final molarity calculation requires careful attention to the grams of lactose present in the solution.

PREREQUISITES
  • Understanding of molarity (M) and its calculation
  • Knowledge of density and its application in solution concentration
  • Familiarity with percentage concentration and its conversion to molarity
  • Basic skills in unit conversion and dimensional analysis
NEXT STEPS
  • Learn how to convert percentage concentration to molarity accurately
  • Study the calculation of molality (m) and its differences from molarity
  • Explore the concept of mole fraction and its significance in solution chemistry
  • Review dimensional analysis techniques for solving chemistry problems
USEFUL FOR

Chemistry students, educators, and anyone involved in solution preparation and concentration calculations will benefit from this discussion.

webz
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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:
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.
 
webz said:
I just want to find the moles of Lactose for now

Moles of lactose in what?

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