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September 21, 2014

Homework Help: Chemistry

Posted by CIndy on Friday, April 27, 2007 at 2:53pm.

What is the molality of a glucose solution prepared by dissolving 18.0g of glucose, C6H12O6 in 125g of water?
A)0.000794
B)0.144
C)0.699
D)0.794

Molality is the number of moles of solute per kilogram of solvent. Because the density of water at 25C is about 1 kilogram per liter, molality is approximately equal to molarity for dilute aqueous solutions at this temperature. This is a useful approximation, but remember that it is only an approximation and doesn't apply when the solution is at a different temperature, isn't dilute, or uses a solvent other than water.

Example:
What is the molality of a solution of 10 g NaOH in 500 g water?

Solution:
10 g NaOH / (4 g NaOH / 1 mol NaOH) = 0.25 mol NaOH
500 g water x 1 kg / 1000 g = 0.50 kg water
molality = 0.25 mol / 0.50 kg
molality = 0.05 M / kg
molality = 0.50 m

hope this helps.....let me know if you need more help


The example looks good but there is a typo. 4g NaOH should read 40 g NaOH/mol.

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