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Chemistry Forums for Students => High School Chemistry Forum => Topic started by: BAMxTiFFANY on March 15, 2009, 03:32:53 PM

Title: uh i actually have no idea? solutions?
Post by: BAMxTiFFANY on March 15, 2009, 03:32:53 PM: so i have this mini quiz thing and im really confused
i need to show work i've gotten 2 of 7
so if you can show me how you did it it would be great
we need to assume like 1 liter of solution or 1 kg of it x]

1. i did it
2. a sodium chloride solution has a molarity of 1.250 mol/L and a density of 1.050g/ml. calculate molality, the mole fraction of water, and the percent by mass of sodium chloride.
3. a solution of potassium nitrated has a molality of .00350 mol/kg and a denisty of 1.009g/ml. calculate the mole fraction of potassium nitrate and the molarity.
^ i got the molarity already
4. one gram of sodium nitrate was dissolved in 100.0 ml of water. the new volume of this solution is 100.1 ml. the density of water is 1.00 g/ml. calculate the molarity, molality, mole fraction of water and the density of this new solution
5.the molarity and molality of a potassium chloride solution are 1.00mol/l and .9750 mol/kg,respectively. calculate the solution's density.
6. ten (10.00) grams of sodium chloride are dissolved in enough water to give you 100.0 ml of solution. one millilter of this new solution is added to enough water to give you a new volume of 110.0 ml. what is the molarity of this new solution?
7. i got it

i would love it if someone helped x]
Title: Re: uh i actually have no idea? solutions?
Post by: ARGOS++ on March 15, 2009, 04:03:30 PM: Dear BAMxTiFFANY;

Can you show us your starting work for each question you ask that we can guide you?

Do you know the definition of molarity, molality, and mole fraction? – Otherwise you may start to ask Wiki for them.

Good Luck!
ARGOS⁺⁺
Title: Re: uh i actually have no idea? solutions?
Post by: BAMxTiFFANY on March 15, 2009, 04:18:36 PM: Quote from: ARGOS++ on March 15, 2009, 04:03:30 PM

Dear BAMxTiFFANY;

Can you show us your starting work for each question you ask that we can guide you?

Do you know the definition of molarity, molality, and mole fraction? – Otherwise you may start to ask Wiki for them.

Good Luck!
ARGOS⁺⁺

yup i do x]

mole fraction > mole of substance over total moles
molarity > mole of solute over liters over solvent
molality > mole of solute over kg of solvent
Title: Re: uh i actually have no idea? solutions?
Post by: ARGOS++ on March 15, 2009, 04:46:27 PM: Dear BAMxTiFFANY;

Except molarity all is correct!
Please try this one again and then start answering question 2.

Good Luck!
ARGOS⁺⁺
Title: Re: uh i actually have no idea? solutions?
Post by: BAMxTiFFANY on March 15, 2009, 05:12:29 PM: Quote from: ARGOS++ on March 15, 2009, 04:46:27 PM

Dear BAMxTiFFANY;

Except molarity all is correct!
Please try this one again and then start answering question 2.

Good Luck!
ARGOS⁺⁺

The number of moles of solute per liter of solution. <molarity O_o my bad
but wut does this have to do?
i dnt how to start this..
Title: Re: uh i actually have no idea? solutions?
Post by: ARGOS++ on March 15, 2009, 05:21:45 PM: Dear BAMxTiFFANY;

Now it’s also ok!

For 2: Can you calculate for the begin who many grams sodium chloride are in 1.00 L solution dissolved, using your definition of molarity?

Good Luck!
ARGOS⁺⁺
Title: Re: uh i actually have no idea? solutions?
Post by: BAMxTiFFANY on March 15, 2009, 05:43:06 PM: Quote from: ARGOS++ on March 15, 2009, 05:21:45 PM

Dear BAMxTiFFANY;

Now it’s also ok!

For 2: Can you calculate for the begin who many grams sodium chloride are in 1.00 L solution dissolved, using your definition of molarity?

Good Luck!
ARGOS⁺⁺

huh O_o begin? who?
like..?

1.050g = xg
1 ml 1000mL (1 L)? so x is.. 1050g dissolved in 1 liter

is that right?
Title: Re: uh i actually have no idea? solutions?
Post by: ARGOS++ on March 15, 2009, 05:50:58 PM: Dear BAMxTiFFANY;

No!, - that’s not correct.

Let’s try it simpler:
a.) How much grams is 1.25 mole of sodium chloride?
b.) And then think about that so much is dissolved in 1.00 L solution!

Good Luck!
ARGOS⁺⁺
Title: Re: uh i actually have no idea? solutions?
Post by: BAMxTiFFANY on March 15, 2009, 05:55:44 PM: Quote from: ARGOS++ on March 15, 2009, 05:50:58 PM

Dear BAMxTiFFANY;

No!, - that’s not correct.

Let’s try it simpler:
a.) How much grams is 1.25 mole of sodium chloride?
b.) And then think about that so much is dissolved in 1.00 L solution!

Good Luck!
ARGOS⁺⁺

a) 73.05
b) is it at STP O_o
Title: Re: uh i actually have no idea? solutions?
Post by: ARGOS++ on March 15, 2009, 06:02:44 PM: Dear BAMxTiFFANY;

That’s exact! - As you are not dealing with gas you must not care about STP.

Now for the next step:
- And now can you tell what the weight of this 1.00 L solution is by using the density?
- How many grams water is contained in this 1.00 L solution?
- And with all that you are able to calculate the molality of the solution using the definition of.

Good Luck!
ARGOS⁺⁺
Title: Re: uh i actually have no idea? solutions?
Post by: BAMxTiFFANY on March 15, 2009, 06:09:47 PM: Quote from: ARGOS++ on March 15, 2009, 06:02:44 PM

Dear BAMxTiFFANY;

That’s exact! - As you are not dealing with gas you must not care about STP.

Now for the next step:
- And now can you tell what the weight of this 1.00 L solution is by using the density?
- How many grams water is contained in this 1.00 L solution?
- And with all that you are able to calculate the molality of the solution using the definition of.

Good Luck!
ARGOS⁺⁺

1. 73.05g/L
2. .804 g?

2.
Title: Re: uh i actually have no idea? solutions?
Post by: ARGOS++ on March 15, 2009, 06:19:30 PM: Dear BAMxTiFFANY;

Your 1.) Is correct for the concentration, but not for the whole weight of the solution.
Only after your 1.) is correct, you are able to calculate how much water is in this 1.00 L solution.
And finally you can calculate the molality.

So please try once again.
Good Luck!
ARGOS⁺⁺
Title: Re: uh i actually have no idea? solutions?
Post by: BAMxTiFFANY on March 15, 2009, 06:27:47 PM: Quote from: ARGOS++ on March 15, 2009, 06:19:30 PM

Dear BAMxTiFFANY;

Your 1.) Is correct for the concentration, but not for the whole weight of the solution.
Only after your 1.) is correct, you are able to calculate how much water is in this 1.00 L solution.
And finally you can calculate the molality.

So please try once again.
Good Luck!
ARGOS⁺⁺

you just confused me -_-
ughh kill me .__.
Title: Re: uh i actually have no idea? solutions?
Post by: ARGOS++ on March 15, 2009, 06:31:47 PM: Dear BAMxTiFFANY;

Let’s try it as simple as before:
If you know the density of 1.050 g/ml, then what is the weight of 1.00 L solution?

Good Luck!
ARGOS⁺⁺
Title: Re: uh i actually have no idea? solutions?
Post by: BAMxTiFFANY on March 15, 2009, 06:35:23 PM: Quote from: ARGOS++ on March 15, 2009, 06:31:47 PM

Dear BAMxTiFFANY;

Let’s try it as simple as before:
If you know the density of 1.050 g/ml, then what is the weight of 1.00 L solution?

Good Luck!
ARGOS⁺⁺

uh O_o
g/v so.. O_O 1050 ? -_-
ugh do you have aim?
Title: Re: uh i actually have no idea? solutions?
Post by: ARGOS++ 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⁺⁺
Title: Re: uh i actually have no idea? solutions?
Post by: BAMxTiFFANY on March 15, 2009, 06:45:54 PM: Quote from: ARGOS++ 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⁺⁺

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?
Title: Re: uh i actually have no idea? solutions?
Post by: ARGOS++ 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⁺⁺
Title: Re: uh i actually have no idea? solutions?
Post by: BAMxTiFFANY on March 15, 2009, 07:08:27 PM: Quote from: ARGOS++ 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⁺⁺

molality > mole of solute over kg of solvent

m = 1.25 solute over .97695 = 1.28mole/kg
Title: Re: uh i actually have no idea? solutions?
Post by: ARGOS++ 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⁺⁺
Title: Re: uh i actually have no idea? solutions?
Post by: BAMxTiFFANY on March 15, 2009, 07:22:41 PM: Quote from: ARGOS++ 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⁺⁺

c) 54.23
d) uh (1.25 over 55.48 ) x100 = 2.25%
Title: Re: uh i actually have no idea? solutions?
Post by: ARGOS++ 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⁺⁺
Title: Re: uh i actually have no idea? solutions?
Post by: BAMxTiFFANY on March 15, 2009, 07:30:19 PM: Quote from: ARGOS++ 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⁺⁺

oh woops so.. .0225?
Title: Re: uh i actually have no idea? solutions?
Post by: ARGOS++ 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⁺⁺
Title: Re: uh i actually have no idea? solutions?
Post by: BAMxTiFFANY on March 15, 2009, 07:45:26 PM: Quote from: ARGOS++ 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⁺⁺

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
Title: Re: uh i actually have no idea? solutions?
Post by: ARGOS++ 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⁺⁺
Title: Re: uh i actually have no idea? solutions?
Post by: BAMxTiFFANY on March 15, 2009, 07:53:34 PM: Quote from: ARGOS++ 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⁺⁺

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
Title: Re: uh i actually have no idea? solutions?
Post by: ARGOS++ 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⁺⁺
Title: Re: uh i actually have no idea? solutions?
Post by: BAMxTiFFANY on March 15, 2009, 08:07:48 PM: Quote from: ARGOS++ 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⁺⁺

O:
im confused again..
Title: Re: uh i actually have no idea? solutions?
Post by: ARGOS++ on March 15, 2009, 08:11:19 PM: Dear BAMxTiFFANY;

What is the definition of % w/w?

Good Luck!
ARGOS⁺⁺
Title: Re: uh i actually have no idea? solutions?
Post by: BAMxTiFFANY on March 15, 2009, 08:20:53 PM: Quote from: ARGOS++ on March 15, 2009, 08:11:19 PM

Dear BAMxTiFFANY;

What is the definition of % w/w?

Good Luck!
ARGOS⁺⁺

you mean percent by mass of sodium chloride
its the mass of sodium over the total mass times 100
Title: Re: uh i actually have no idea? solutions?
Post by: ARGOS++ on March 15, 2009, 08:30:00 PM: Dear BAMxTiFFANY;

Correct!, - So please calculate it!

Good Luck!
ARGOS⁺⁺
Title: Re: uh i actually have no idea? solutions?
Post by: BAMxTiFFANY on March 15, 2009, 08:34:12 PM: soo its.. 2.25% :]
Title: Re: uh i actually have no idea? solutions?
Post by: ARGOS++ on March 15, 2009, 08:40:39 PM: Dear BAMxTiFFANY;

Sorry - NO!

If I remember correctly:
Quote from: ARGOS++ on March 15, 2009, 06:40:15 PM
Now we know that 1.050 kg solution contains 73.05 g sodium chloride.

Good Luck!
ARGOS⁺⁺
Title: Re: uh i actually have no idea? solutions?
Post by: BAMxTiFFANY on March 15, 2009, 08:57:57 PM: Quote from: ARGOS++ on March 15, 2009, 08:40:39 PM

Dear BAMxTiFFANY;

Sorry - NO!

If I remember correctly:
Quote from: ARGOS++ on March 15, 2009, 06:40:15 PM
Now we know that 1.050 kg solution contains 73.05 g sodium chloride.

Good Luck!
ARGOS⁺⁺

um you just confused me O_O
is it .696?
Title: Re: uh i actually have no idea? solutions?
Post by: ARGOS++ on March 15, 2009, 09:05:59 PM: Dear BAMxTiFFANY;

Closer! (But still far by factor 10.)

But if I remember correctly:
Quote from: ARGOS++ on March 15, 2009, 06:55:10 PM
!!!!!! Please calculate all times with units !!!!!!!

Please re-calculate it!

I think you confuse yourself most!!
Good Luck!
ARGOS⁺⁺
Title: Re: uh i actually have no idea? solutions?
Post by: BAMxTiFFANY on March 15, 2009, 09:39:50 PM: Quote from: ARGOS++ on March 15, 2009, 09:05:59 PM

Dear BAMxTiFFANY;

Closer! (But still far by factor 10.)

But if I remember correctly:
Quote from: ARGOS++ on March 15, 2009, 06:55:10 PM
!!!!!! Please calculate all times with units !!!!!!!

Please re-calculate it!

I think you confuse yourself most!!
Good Luck!
ARGOS⁺⁺

uh

its ..73.05 over 1050
then times 100.. soo 6.96%
Title: Re: uh i actually have no idea? solutions?
Post by: ARGOS++ on March 15, 2009, 09:43:59 PM: Dear BAMxTiFFANY;

Exact!

Now we have finished your Question 2.). Study it very! very carefully once again!!

Please try the other questions by yourself and tell where you run in troubles.
Hint for question 3.):
What is the definition of molality telling you about the solvent (water)?

Good Luck!
ARGOS⁺⁺
Title: Re: uh i actually have no idea? solutions?
Post by: BAMxTiFFANY on March 15, 2009, 10:01:54 PM: Quote from: ARGOS++ on March 15, 2009, 09:43:59 PM

Dear BAMxTiFFANY;

Exact!

Now we have finished your Question 2.). Study it very! very carefully once again!!

Please try the other questions by yourself and tell where you run in troubles.
Hint for question 3.):
What is the definition of molality telling you about the solvent (water)?

Good Luck!
ARGOS⁺⁺

thanks! x]
i already did the molality for #3 i just cant get mole fraction for water..