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Topic: number of moles in br2 solution  (Read 1398 times)

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yitzik

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number of moles in br2 solution
« on: July 22, 2021, 02:50:37 PM »
hello!
how can i calculate the number of moles of br2 in a solution of 10% (by mass) of br2 in  dichloromethane?
there is no available data about the density of such a solution, so how can i deduce it's molarity?
what is the right way to solve it?

thanks!

Orcio_Dojek

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Re: number of moles in br2 solution
« Reply #1 on: July 22, 2021, 04:32:49 PM »
1. Find the density of 10 % (by weight) solution of Br2 in CH2Cl2.
2. Calculate mass of 1000 ml of this solution.
3. Divide quantity (number of moles) of Br2 per volume of the solution (1 liter).

Borek

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Re: number of moles in br2 solution
« Reply #2 on: July 23, 2021, 04:17:46 AM »
there is no available data about the density of such a solution, so how can i deduce it's molarity?

You can't.
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yitzik

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Re: number of moles in br2 solution
« Reply #3 on: July 23, 2021, 06:38:14 AM »
how can i calculate the number of moles of br2 in a solution of 10% (by weight) of br2 in  dichloromethane?
i'm asked to find the number of moles in 30 ml of such a solution, so there must be a way to do this..
maybe there is a way to calculate the average density of the two substances? or weighted mean of the densities or something like that?

thanks!

Orcio_Dojek

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Re: number of moles in br2 solution
« Reply #4 on: July 23, 2021, 08:03:05 AM »
True, as density of the solution grows linearly with the growth of mass concentration (fits the y = a + bx function).

Borek

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Re: number of moles in br2 solution
« Reply #5 on: July 23, 2021, 11:12:38 AM »
maybe there is a way to calculate the average density of the two substances? or weighted mean of the densities or something like that?

Sorry, but no.

You can do some approximations, but volumes are not additive, so you never know what kind of error you make.

If you have no density tables best you can do is to take just the density of the solvent and pray the error won't be too large.
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Borek

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Re: number of moles in br2 solution
« Reply #6 on: July 23, 2021, 11:19:16 AM »
True, as density of the solution grows linearly with the growth of mass concentration (fits the y = a + bx function).

Here is a "straight line" for the acetic acid.
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Orcio_Dojek

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Re: number of moles in br2 solution
« Reply #7 on: July 23, 2021, 03:07:42 PM »
@Borek yitzik asked about 10 % solution of Br2 in CH2Cl2. To point of about 40- 50 % conc. density of acetic acid does not differ that much from y = a + bx.

Borek

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Re: number of moles in br2 solution
« Reply #8 on: July 23, 2021, 03:22:00 PM »
1. You never said it holds for low concentrations only, you stated it as if it was a general rule. It is not.

2. OP doesn't have the data to fit the line, so your advice is still useless.
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Orcio_Dojek

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Re: number of moles in br2 solution
« Reply #9 on: July 23, 2021, 04:02:21 PM »
Still not so useless as "taking just the density of the solvent and pray the error won't be too large".

Borek

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Re: number of moles in br2 solution
« Reply #10 on: July 23, 2021, 06:31:32 PM »
Then explain how to use your advice to solve the problem at hand, when the density of dichlorometane is the only data point.
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billnotgatez

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Re: number of moles in br2 solution
« Reply #11 on: July 24, 2021, 09:12:19 AM »
@yitzik
Based on the 2 entries you have made it appears we do not have the question as asked  to you in a complete form
Can you post it as given to you

hello!
how can i calculate the number of moles of br2 in a solution of 10% (by mass) of br2 in  dichloromethane?
there is no available data about the density of such a solution, so how can i deduce it's molarity?
what is the right way to solve it?

thanks!

how can i calculate the number of moles of br2 in a solution of 10% (by weight) of br2 in  dichloromethane?
i'm asked to find the number of moles in 30 ml of such a solution, so there must be a way to do this..
maybe there is a way to calculate the average density of the two substances? or weighted mean of the densities or something like that?

thanks!

Orcio_Dojek

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Re: number of moles in br2 solution
« Reply #12 on: July 24, 2021, 10:01:11 AM »
@Borek

I would use google to find density of any dilute Br2 - CH2Cl2 solution, and then calculate approximate density of 10 % Br2 solution.

I don't believe that there are no data at all.

yitzik

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Re: number of moles in br2 solution
« Reply #13 on: July 24, 2021, 02:52:57 PM »
Quote
how can i calculate the number of moles of br2 in a solution of 10% (by mass) of br2 in  dichloromethane?
thanks for the replies, this is a pre lab question... i need to calculate the number of moles but any additional data is not geiven and i'm asked to search in the net.
sigma aldrich does't sell such a solution.... couldn't find any other data about the density...

thanks