xomaxhox
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I'm currently doing research into my potential chemistry coursework for A2 OCR B (Salters) and will be doing the determination of copper in a brass sample.

So far through practise all of my techniques for accuracy testing with Copper (II) sulfate have been fine, and today was my first attempt at dissolving the brass sample for use.

I will be using the Nernst equation in my coursework and so will be using the dissolved brass sample as part of an electrochemical cell as the copper half cell, although this obviously caused some problems to arise, which is why I am now requesting help!


Being part copper, part zinc, creating a copper half cell from brass will obviously require the removal of the zinc from the solution as the other half cell will involve zinc and I don't want to hinder my results.

My plan, therefore, was:
  1. dissolve the brass sample in conc nitric acid with the end point being when no more NO2 fumes are released
  2. add excess Fe filings to displace the zinc
  3. add dilute (2 M) HCl to dissolve the zinc and iron
  4. filter to leave the copper nitrate solution for use in the half cell



Can anyone see anything wrong with this method, which although is long winded, is necessary for use in a half cell (as far as I know), and also what colour should the solution be after stages 2 and 3?


Many thanks.
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Borek
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No idea about the requested procedure, so I can't comment on most of your problems. However, I can comment on a chemistry.

(Original post by xomaxhox)
add excess Fe filings to displace the zinc
Won't work.
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Phteven
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(Original post by xomaxhox)
I'm currently doing research into my potential chemistry coursework for A2 OCR B (Salters) and will be doing the determination of copper in a brass sample.

So far through practise all of my techniques for accuracy testing with Copper (II) sulfate have been fine, and today was my first attempt at dissolving the brass sample for use.

I will be using the Nernst equation in my coursework and so will be using the dissolved brass sample as part of an electrochemical cell as the copper half cell, although this obviously caused some problems to arise, which is why I am now requesting help!


Being part copper, part zinc, creating a copper half cell from brass will obviously require the removal of the zinc from the solution as the other half cell will involve zinc and I don't want to hinder my results.

My plan, therefore, was:
  1. dissolve the brass sample in conc nitric acid with the end point being when no more NO2 fumes are released
  2. add excess Fe filings to displace the zinc
  3. add dilute (2 M) HCl to dissolve the zinc and iron
  4. filter to leave the copper nitrate solution for use in the half cell



Can anyone see anything wrong with this method, which although is long winded, is necessary for use in a half cell (as far as I know), and also what colour should the solution be after stages 2 and 3?


Many thanks.
I think iron is less reactive the zinc so there won't be any displacement. Not sure though!


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charco
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(Original post by xomaxhox)
I'm currently doing research into my potential chemistry coursework for A2 OCR B (Salters) and will be doing the determination of copper in a brass sample.

So far through practise all of my techniques for accuracy testing with Copper (II) sulfate have been fine, and today was my first attempt at dissolving the brass sample for use.

I will be using the Nernst equation in my coursework and so will be using the dissolved brass sample as part of an electrochemical cell as the copper half cell, although this obviously caused some problems to arise, which is why I am now requesting help!


Being part copper, part zinc, creating a copper half cell from brass will obviously require the removal of the zinc from the solution as the other half cell will involve zinc and I don't want to hinder my results.

My plan, therefore, was:
  1. dissolve the brass sample in conc nitric acid with the end point being when no more NO2 fumes are released
  2. add excess Fe filings to displace the zinc
  3. add dilute (2 M) HCl to dissolve the zinc and iron
  4. filter to leave the copper nitrate solution for use in the half cell


Can anyone see anything wrong with this method, which although is long winded, is necessary for use in a half cell (as far as I know), and also what colour should the solution be after stages 2 and 3?

Many thanks.
If you follow through what is in the mix after each step you will see that it's unfeasible.

Adding nitric acid is OK and will give you a mixture of copper nitrate, zinc nitrate and excess nitric acid.

Excess iron filings will then displace the copper (not the zinc) - why not use zinc metal in the first place as it's already there in solution?

However, there are other standards methods for doing what you are trying, why not do a bit more research to get an accepted method?
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xomaxhox
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Thanks for the responses, I had mixed up zinc and iron's position in the reactivity series!

So I guess what should in fact happen is that in the end the displaced copper solid should be filtered out leaving a green iron (II) nitrate solution instead.

I suppose I can then just dry and dissolve the copper in sulfuric acid to form copper sulfate for use in the electrochemical cell.



(Original post by charco)
...
However, there are other standards methods for doing what you are trying, why not do a bit more research to get an accepted method?
I had tried looking for methods resulting in the same final outcome but couldn't seem to find any. The only ones I did find left the zinc in the solution because they were instead using the copper for a titration rather than electrochemical cell.
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charco
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(Original post by xomaxhox)
Thanks for the responses, I had mixed up zinc and iron's position in the reactivity series!

So I guess what should in fact happen is that in the end the displaced copper solid should be filtered out leaving a green iron (II) nitrate solution instead.

I suppose I can then just dry and dissolve the copper in sulfuric acid to form copper sulfate for use in the electrochemical cell.

I had tried looking for methods resulting in the same final outcome but couldn't seem to find any. The only ones I did find left the zinc in the solution because they were instead using the copper for a titration rather than electrochemical cell.
*sigh*

Here's a tip.

A website I use a lot is called "Google". You could try using it (www.google.com) you'll find it very useful ...
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