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Topic: Molarity vs Molality  (Read 12820 times)

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Offline ARGOS++

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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++


Offline 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

Offline ARGOS++

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Re: Molarity vs Molality
« Reply #17 on: December 01, 2008, 04:56:52 PM »
Dear student8607;

Please control again! (masstotal is ok!)

But I got:  1046.5g / 1.0173 g/ml = 1028.7 ml (= voltotal)
(If density is finally correct.)


Good Luck!
                    ARGOS++


Offline 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  ;)


Offline 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++


Offline student8607

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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

Offline student8607

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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?

Offline 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  :o

Offline 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++


Offline Borek

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