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Molarity vs Molality
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Topic: Molarity vs Molality (Read 16067 times)
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ARGOS++
Sr. Member
Posts: 1489
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Re: Molarity vs Molality
«
Reply #15 on:
December 01, 2008, 04:39:51 PM »
Dear
student8607
;
Please control your last calculation; you did a
BIG
comma mistake!
Use the Units for control!
And if you have corrected it, then calculate the final molaRity from it.
Good Luck!
ARGOS
++
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student8607
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Re: Molarity vs Molality
«
Reply #16 on:
December 01, 2008, 04:48:56 PM »
yeah i see that my calculations has way too many zeroes
but i doubled checked
density was given in g/mL
and we said 1kg for solvent. so that's 1000g + the 46.5g of solute from the molality
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ARGOS++
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Re: Molarity vs Molality
«
Reply #17 on:
December 01, 2008, 04:56:52 PM »
Dear
student8607
;
Please control again! (mass
total
is ok!)
But I got: 1046.5g / 1.0173 g/ml = 1028.7 ml (= vol
total
)
(If density is finally correct.)
Good Luck!
ARGOS
++
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student8607
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Re: Molarity vs Molality
«
Reply #18 on:
December 01, 2008, 05:49:01 PM »
oh you are right
it is mass over density not the other way around
so then 0.2588mol/1.028L = 0.251M
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ARGOS++
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Re: Molarity vs Molality
«
Reply #19 on:
December 01, 2008, 05:54:24 PM »
Dear
student8607
;
You did it!
- Hard but
ultimately!
Repeat the small conversion once again, to “get” really behind it!
Good Luck!
ARGOS
++
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student8607
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Posts: 227
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Re: Molarity vs Molality
«
Reply #20 on:
December 01, 2008, 05:58:11 PM »
YAY - thanks very much
so i got bold and tried another problem (molarity to molality)
and i failed
The density of a 0.500M solution of acetic acid in water is 1.0042g/mL. What is the molality?
Molar mass is 60.05g
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student8607
Full Member
Posts: 227
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Re: Molarity vs Molality
«
Reply #21 on:
December 01, 2008, 05:59:33 PM »
0.5mol acetic acid = 30.025g of acetic acid
D times V = total mass
(1.0042g/mL)(1000mL from the 0.500M) = 1004g total
so i figured 1004-30.025 would be grams of solvent (0.974kg)
0.5mol / 0.974kg = 0.513?
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student8607
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Re: Molarity vs Molality
«
Reply #22 on:
December 01, 2008, 06:04:09 PM »
oh wait, my fault, that WAS correct
0.513 is right
yay
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ARGOS++
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Re: Molarity vs Molality
«
Reply #23 on:
December 01, 2008, 06:06:41 PM »
Dear
student8607
;
Correct!
Good Luck!
ARGOS
++
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Borek
Mr. pH
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I am known to be occasionally wrong.
Re: Molarity vs Molality
«
Reply #24 on:
December 01, 2008, 06:52:47 PM »
Examples of general approach:
http://www.chembuddy.com/?left=concentration&right=percentage-to-molarity
http://www.chembuddy.com/?left=concentration&right=percentage-to-molality
And ultimate approach:
http://www.chembuddy.com/?left=CASC&right=concentration-cheat-sheet
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ChemBuddy
chemical calculators - stoichiometry, pH, concentration, buffer preparation,
titrations.info
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