Chemical Forums
Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: student8607 on December 01, 2008, 07:33:35 AM
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This is all I am given:
Assume seawater is a 3.50% solution of NaCl. What is the molality of the solution?
Mass % = [mass component / total mass] x 100
molality = mol solute / kg solvent
Can I use NaCl's molar mass of 58.5g somewhere in the mass percent?
Where am I supposed to get the rest of the numbers from to calculate?
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Dear student8607;
Yes, - “your” molar mass of NaCl is correct.
Think about how total mass is related to mass solute and mass solvent and mass%.
So you don’t need something else.
Good Luck!
ARGOS++
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total mass = mass% / 100?
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Dear student8607;
More important for you is: masstotal = mass Solute + mass Solvent!
(I think you know how to use it in mass%.)
Good Luck!
ARGOS++
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i think that is what i was trying to get at
so since the total 3.50%, does that mean the total mass is 3.50g?
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Dear student8607;
No!, - Contrary you’re allowed to select the masstotal free! So select 1.00 kg for it to make it easy.
Good Luck!
ARGOS++
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Dear student8607;
Try it this way: How much is 3.50 %w/w of 1.00 kg, and how much mass is left for the Solvent.
Good Luck!
ARGOS++
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oh yes. dumb me.
so, 3.50% of 1k (1000g) is 35g of NaCl
there are 965g left over as the solvent
molality = mol solute / kg solvent
0.60mol / 0.965kg = 0.62!
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Dear student8607;
Bravo!, - You did it! Now you can try the other question.
Good Luck!
ARGOS++