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Topic: Help please  (Read 14667 times)

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Offline mass

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Help please
« on: February 27, 2008, 01:20:50 PM »
thanks.
« Last Edit: March 05, 2008, 03:44:28 PM by mass »

Offline JGK

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Re: Help please
« Reply #1 on: February 27, 2008, 02:07:35 PM »
I take it cm3= ml?

Are you serious?  I suggest you read a basic text on measurement units

http://www.unc.edu/~rowlett/units/

Experience is something you don't get until just after you need it.

Online Borek

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Re: Help please
« Reply #2 on: February 27, 2008, 02:10:06 PM »
Please read forum rules. Subject "Help me" doesn't tell anything about your problem.

To be honest - even after reading your post I have no idea what you are asking about. The only answer to only question yous posted is "yes".
« Last Edit: February 27, 2008, 02:23:32 PM by Borek »
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Offline mass

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Re: Help please
« Reply #3 on: February 27, 2008, 03:01:16 PM »
I am asking how to do the calculations the question is asking for?

Online Borek

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Re: Help please
« Reply #4 on: February 27, 2008, 03:15:21 PM »
Start with reaction equations and definitions of things you have to calculate.
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Offline JGK

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Re: Help please
« Reply #5 on: February 27, 2008, 03:23:32 PM »
Unless you start showing some progress this thread will probably get locked (Inote that this is your second thread today on the same subject.

I think Point 4 of the forum rules sums things up nicely.

"4.) Please show that you've at least attempted the problem.  We don't mind helping you solve problems but we are ethically opposed to doing homework for you. Violators will have their topic deleted or locked."
Experience is something you don't get until just after you need it.

Offline mass

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Re: Help please
« Reply #6 on: February 27, 2008, 04:39:18 PM »
jesus christ, i honestly don't know where to start hnece I am asking.

Offline Arkcon

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Re: Help please
« Reply #7 on: February 27, 2008, 04:51:11 PM »
A suggestion:  read your book again, write down information that's pertinent on a piece of scrap paper, and use it to solve some of the problems.  Show us what you have, and what you've written down, and we'll help you with some places you're stuck.

And ditch the scanner -- you're robbing yourself of a chance to write down what you've read to help yourself understand it better.  Look at this question: http://www.chemicalforums.com/index.php?topic=23190.msg88389#msg88389
Someone scanned a problem and couldn't solve it, they didn't even realize they hadn't read it correctly.
Hey, I'm not judging.  I just like to shoot straight.  I'm a man of science.

Offline mass

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Re: Help please
« Reply #8 on: February 28, 2008, 05:48:06 PM »
I am not trying to get anyone to do my work. At university there is no guidance and hence we are all struggling. Therefore, I am having to use this forum for help. I know the equations relating to partition coefficient but I want to know how on earth you can use them?

Online Borek

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Re: Help please
« Reply #9 on: February 28, 2008, 06:36:30 PM »
I know the equations relating to partition coefficient but I want to know how on earth you can use them?

Most likely you have to find a way to find concentrations that you should put into the partition coefficient definition... You know initial amount of benzoic acid, this will not change for obvious reasons, although it will be split between two phases. Titration is a way of determining amount of the acid in the water - do you know what reaction takes place?
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Offline DrCMS

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Re: Help please
« Reply #10 on: February 29, 2008, 04:17:18 AM »
Stop and think what you have just measured.

You were given a sample of known concentration of benzoic acid. 
It is a week acid therefore it was not fully ionized

You have a titration value for a benzoic acid sample + buffer that was extracted with DCM.  What might the DCM remove?

You have a titration value for buffer alone extracted with DCM.

What is the difference between the above titrations, so therefore what can you now calculate. 

How does that value compare with the given concentration of the original sample? 

Offline mass

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Re: Help please
« Reply #11 on: February 29, 2008, 09:18:10 AM »
I know the equations relating to partition coefficient but I want to know how on earth you can use them?

Most likely you have to find a way to find concentrations that you should put into the partition coefficient definition... You know initial amount of benzoic acid, this will not change for obvious reasons, although it will be split between two phases. Titration is a way of determining amount of the acid in the water - do you know what reaction takes place?

I am not sure about the reaction taking place. Could I use n=cv/1000 and find the conetration  ???

Online Borek

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Re: Help please
« Reply #12 on: February 29, 2008, 09:36:10 AM »
Neutralization.

Could I use n=cv/1000 and find the conetration  ???

If I will answer yes - will you know what you are doing? If I will answer no - will it help you understand anything? Calculation have to reflect stoichiometry of the reaction taking place. As long as you don't know the reaction, you can't use some equation taken out of the thin air and hope it'll be OK.
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Offline mass

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Re: Help please
« Reply #13 on: February 29, 2008, 10:29:33 AM »
no I don't get it still ,whats the equation though? sorry my level of chemistry has become so poor since I have come to uni.

Offline JGK

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Re: Help please
« Reply #14 on: February 29, 2008, 11:16:35 AM »
I believe you were already given one of the  reaction "equation" here:
http://www.chemicalforums.com/index.php?topic=23518.0

I suggest you:

1. calculate the [H+] present  from the titration data in the "test" section of the problem.

    this gives you the following information pH (from your measurement),Pka (listed) and [H+].

Check you textbook (in the chapter on pH) and find an equation which requires all of the above (and contains an unknown quantity).

2. Calculate the value of the unknown.

3. Repeat step 1 for the blank.

This should supply you with all the information you need to answer the questions.





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