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### Topic: uh i actually have no idea? solutions?  (Read 18879 times)

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#### ARGOS++

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##### Re: uh i actually have no idea? solutions?
« Reply #15 on: March 15, 2009, 06:40:15 PM »

Dear BAMxTiFFANY;

Nearly correct!, - but you forgot the units!

Now we know that 1.050 kg solution contains 73.05 g sodium chloride.
a.)    How much grams are left for water?
b.)    And what’s then the molality?

Good Luck!
ARGOS++

#### BAMxTiFFANY

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##### Re: uh i actually have no idea? solutions?
« Reply #16 on: March 15, 2009, 06:45:54 PM »

Dear BAMxTiFFANY;

Nearly correct!, - but you forgot the units!

Now we know that 1.050 kg solution contains 73.05 g sodium chloride.
a.)    How much grams are left for water?
b.)    And what’s then the molality?

Good Luck!
ARGOS++

um 976.95g h20 O_o
73.05 over 976.95 which is.. .07477mole/kg?

now i have to show how i did it on paper O_o
how do i do that?

#### ARGOS++

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##### Re: uh i actually have no idea? solutions?
« Reply #17 on: March 15, 2009, 06:55:10 PM »

Dear BAMxTiFFANY;

The weight of water is correct!

But then you are toooo fast and that’s why it is not correct:  73.05g are not 0.07305 moles!
!!!!!! Please calculate all times with units  !!!!!!!

So remember: 73.05g are 1.25 moles sodium chloride! So what’s now the result for b.)?

Good Luck!
ARGOS++

#### BAMxTiFFANY

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##### Re: uh i actually have no idea? solutions?
« Reply #18 on: March 15, 2009, 07:08:27 PM »

Dear BAMxTiFFANY;

The weight of water is correct!

But then you are toooo fast and that’s why it is not correct:  73.05g are not 0.07305 moles!
!!!!!! Please calculate all times with units  !!!!!!!

So remember: 73.05g are 1.25 moles sodium chloride! So what’s now the result for b.)?

Good Luck!
ARGOS++

molality > mole of solute over kg of solvent

m =  1.25 solute over .97695 = 1.28mole/kg

#### ARGOS++

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##### Re: uh i actually have no idea? solutions?
« Reply #19 on: March 15, 2009, 07:12:53 PM »

Dear BAMxTiFFANY;

Bravo!,  - That’s exact!

And now:
c.)  How many moles are this 976.95g water?
d.)  What’s now the mole fraction?

Good Luck!
ARGOS++

#### BAMxTiFFANY

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##### Re: uh i actually have no idea? solutions?
« Reply #20 on: March 15, 2009, 07:22:41 PM »

Dear BAMxTiFFANY;

Bravo!,  - That’s exact!

And now:
c.)  How many moles are this 976.95g water?
d.)  What’s now the mole fraction?

Good Luck!
ARGOS++

c) 54.23
d) uh (1.25 over 55.48 ) x100 = 2.25%

#### ARGOS++

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##### Re: uh i actually have no idea? solutions?
« Reply #21 on: March 15, 2009, 07:28:14 PM »

Dear BAMxTiFFANY;

C.) is correct!

For d.) remember its definition!mole-fraction is unit-less! So you have not to multiply be 100!
Can you do d.) once again?

Good Luck!
ARGOS++

#### BAMxTiFFANY

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##### Re: uh i actually have no idea? solutions?
« Reply #22 on: March 15, 2009, 07:30:19 PM »

Dear BAMxTiFFANY;

C.) is correct!

For d.) remember its definition!mole-fraction is unit-less! So you have not to multiply be 100!
Can you do d.) once again?

Good Luck!
ARGOS++

oh woops so.. .0225?

#### ARGOS++

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##### Re: uh i actually have no idea? solutions?
« Reply #23 on: March 15, 2009, 07:37:27 PM »
Dear BAMxTiFFANY;

Exact!

Now can you finally calculate the % w/w of the solution?

Good Luck!
ARGOS++

#### BAMxTiFFANY

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##### Re: uh i actually have no idea? solutions?
« Reply #24 on: March 15, 2009, 07:45:26 PM »
Dear BAMxTiFFANY;

Exact!

Now can you finally calculate the % w/w of the solution?

Good Luck!
ARGOS++

2.25% :]

dude your my new bff O:
can you help me with numero tres?
i can't figure out how to find the total moles for water..
i assumed 1 kg of kno3 and i got 9.89 moles of KNO3

#### ARGOS++

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##### Re: uh i actually have no idea? solutions?
« Reply #25 on: March 15, 2009, 07:49:08 PM »

Dear BAMxTiFFANY;

Sorry!% w/w has nothing to do with mole-fraction!
Please use the definition of % w/w!

Good Luck!
ARGOS++

#### BAMxTiFFANY

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##### Re: uh i actually have no idea? solutions?
« Reply #26 on: March 15, 2009, 07:53:34 PM »

Dear BAMxTiFFANY;

Sorry!% w/w has nothing to do with mole-fraction!
Please use the definition of % w/w!

Good Luck!
ARGOS++

um it said percent by mass of sodium
and mole fraction of water :|
so you kinda got it backwards.. i think O:
its i think.. 2.25% and .9775

#### ARGOS++

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##### Re: uh i actually have no idea? solutions?
« Reply #27 on: March 15, 2009, 07:57:21 PM »

Dear BAMxTiFFANY;

That’s not correct!,  -  w/w = weight/weight has nothing to do with moles too.

Good Luck!
ARGOS++

#### BAMxTiFFANY

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##### Re: uh i actually have no idea? solutions?
« Reply #28 on: March 15, 2009, 08:07:48 PM »

Dear BAMxTiFFANY;

That’s not correct!,  -  w/w = weight/weight has nothing to do with moles too.

Good Luck!
ARGOS++

O:
im confused again..

#### ARGOS++

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##### Re: uh i actually have no idea? solutions?
« Reply #29 on: March 15, 2009, 08:11:19 PM »

Dear BAMxTiFFANY;

What is the definition of % w/w?

Good Luck!
ARGOS++