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Topic: Molality Problem  (Read 2427 times)

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Offline 4evrastudent

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Molality Problem
« on: March 04, 2014, 03:35:04 AM »
I am given a 1.457 M solution of maltose with a density of 1.188 g/mL. I'm asked to find the molality. Here is my work:

(1.457 mol maltose / 1 L H2O) * (1.00 L H2O / 1000 mL H2O) * (mL H2O / 1.188 g H2O) * (1000 g H2O / 1 kg H2O) = 1.23 m

The issue is that the answer key gives the answer as 2.11. Could someone help guide me towards my mistake? Thanks!

Offline Borek

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Re: Molality Problem
« Reply #1 on: March 04, 2014, 04:23:22 AM »
(mL H2O / 1.188 g H2O)

This is not 1.188 g of H2O, but 1.188 g of solution.

As far as I can tell this is not just a simple application of conversion factors. Assume you have 1 L of the solution, find number of moles of maltose and mass of solvent, then use these to calculate molality.

2.11 m is a correct answer btw.
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