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Chemistry Forums for Students => High School Chemistry Forum => Topic started by: 4evrastudent on March 04, 2014, 03:35:04 AM

Title: Molality Problem
Post by: 4evrastudent 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!

Title: Re: Molality Problem
Post by: Borek on March 04, 2014, 04:23:22 AM

Quote from: 4evrastudent on March 04, 2014, 03:35:04 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.