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Josh C
#1 Posted : Friday, July 22, 2011 11:08:20 PM
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Which solution is more concentrated and why? 1 molarity of NaCl, or 1 Molality of NaCl?
I was not clear on this section when it was discussed in the lecture. Help would be greatly appreciated!
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JC
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matthewward
#2 Posted : Saturday, July 23, 2011 9:50:53 PM
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1M is more concentrated than 1m. Think about it this way:

1M of NaCl could be prepared by taking 1 mol of NaCl and adding it to water until a volume of 1L is reached.

1m of NaCl would be prepared by taking 1 mol of NaCl and 1kg of water (1L) and adding the two together. Technically then, the 1m solution takes up slightly more volume than the 1M solution and even though both solutions have exactly 1 mol of NaCl in them, the 1m solution would be SLIGHTLY less concentrated than the 1M solution.

For all practical purposes the two concentrations are identical (1M and 1m) - but you know the MCAT:) Your EK book does a similiar problem in one of the 24 practice problems from chapter 4 (I believe).
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