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    Hi TSR,

    So I am a level 3 student currently working on some Chemistry homework looking at separation techniques.

    Can you help? Any input is welcomed! Please read on. Please note that my work is set out in Standard experimental report format e.g. Introduction, method, results, analysis, conclusion and evaluation. I am currently typing it up in MS word.

    1. Plan an experiment to separate the components in the following mixture:

    Potassium bromide and aluminium oxide.

    Your plan should include:
    (i) Experimental details on how you will carry out the separation and the reasons why you have chosen the method described.

    (ii) Details about how you could find the % of aluminium oxide in the original mixture.

    (iii) How you could test the aluminium oxide to see if any potassium bromide was present after separation.

    2. Briefly describe how you would carry out separations of the following mixtures. Give reasons why you have chosen the method described and include any tests you would carry out to demonstrate the efficiency of the separation (where appropriate)

    (i) Two liquids X and Y. X boils at 70 degrees Celsius and Y boils at 110 degrees Celsius. X is flammable, Y is not.

    (ii) Iodine and sodium nitrate

    (iii) Pigments in plant leaves

    Some useful information:
    Aluminium oxide - Insoluble in water
    Potassium bromide - Soluble in water
    Iodine - Insoluble in water - Soluble in non-polar solvents
    Sodium nitrate - Soluble in water - Insoluble in non-polar solvents

    ******************************** ******************************** ******************************** ***************

    Standard Experimental report format:

    WRITING A REPORT OF ANEXPERIMENT:

    Write the report as soon as possible after theexperiment. Don’t leave it too long elseyou will forget the details or lose the results! (I speak from personal experience!) When describing the procedure, DO NOT write in thefirst person i.e. do NOT say ‘I added 50cm3 of sulphuric acid to abeaker..’. This is not the style inwhich scientific reports are written. It might have been acceptable at GCSE but you have progressed beyondthat now. Research reports andscientific papers are written in what is called the ‘3rd person pastpassive’. e.g. ‘Sulphuric acid(50cm3) was added to a beaker which was then heated etc etc’.‘Asolution of copper (II) sulphate in water wasprepared…’‘5drops of silver nitrate solution were added toan aqueous solution of sodium chloride. A white precipitate was obtained’

    When writing a report, you need the following mainsections ·

    Introduction: give the aim of the experiment and anyrelevant theory behind it. Ifappropriate give a prediction ·

    Method: What did you do? Give full experimental detail. Draw a diagram of the apparatus if you thinkit useful. How did you get theresults? How many results? ·

    Results: Tabulate these wherever possible. Set your results out clearly. Write them in the appropriate place on themethod sheet not on odd bits of paper which can be easily lost! ·

    Analysis of results: Can you carry out any further analysis ofthe results? e.g. plot a graph or barchart? Carry out any further calculations? ·

    Conclusion- What do the results tell you? Do they confirm your prediction if you madeone? ·

    Evaluation -how well did the experiment work? Werethe results all OK or were some ‘odd’? What could you do to make the experiment better? Are there any further experiments you coulddo to provide further information about the topic being studied? · Give all graphs, plots, diagrams etc a title. Make sure that you label the axes of graphsand state the units. Use a sensiblescale for graphs. ·

    Rememberthat not all the above points will be appropriate for every experiment. Use your judgement.

    There is my task. I have some notes but they are not proving helpful enough. We have done a similar experiment with ethanol production using the distillation technique. However my group compiled no results and we had some interruptions going on.

    Please provide me with any input you can, on any aspect it doesn't have to be in order. Any input is good input.

    Many thanks.

    A-tav.
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    Disclaimer: Completely going off my own knowledge with this and I'm currently an A level student, so feel free to completely disagree with what I write.

    Potassium bromide and Aluminium oxide:
    You mentioned that potassium bromide is soluble whereas aluminium oxide isn't - would make sense therefore to add an (excess of) solvent (water in this case) to dissolve the potassium bromide.
    Dissolving KBr in solution would produce KBr(s) -> K+(aq) + Br-(aq)

    The steps would be:
    1. Add excess water to the sample containing aluminium oxide and potassium bromide
    2. Stir sample (for x number of minutes) in order to homogenise the mixture so that the potassium bromide, that is soluble, dissolves fully.
    3. Get a beaker and place a funnel with filter paper in the funnel and then pour mixture through funnel. This should leave the solid aluminium oxide in the filter paper and the potassium bromide solution should filter through into the beaker.
    4. Not sure what exactly the correct methodology is from here, but what I would say is: wash the aluminium oxide with cold water (to remove any of the solution) and then dry with filter paper. This should leave you with the desired aluminium oxide.
    5. To get back the potassium bromide, just heat the water to evaporate all the water of the solution until what is left is potassium bromide. Again you can then dry this with filter paper to ensure there is no excess water remaining.

    I don't really have time to write in detail the rest of the separations but my ideas are:

    Finding % of aluminium oxide: Probably some sort of acid-base titration is required

    Test for any potassium bromide: Don't know if this allowed (since you'll lose the sample) but the silver nitrate test is the standard test for bromide ions. If this correct, you can go the extra mile and say to use ammonia to distinguish between bromide ions and iodide ions.

    Flammable and non-flammable gas: I would be thinking of fractional distillation, but the flammable and non-flammable part sounds interesting. Perhaps at those temperatures it could lead to a combustion reaction, so use a reducing environment (one with oxygen and other oxidising agents removed)?

    Iodine and sodium nitrate: Sort of similar to the potassium bromide/aluminium oxide separation (maybe even the same). The non-polar solvent is probably something like toluene (methylbenzene (essentially hydrocarbons).

    Pigments in plant leaves: Ok i feel comfortable with this since I'm much better at biology. Essentially:
    1. Blender to break up the plant leaves (cell wall of cells and chloroplast membrane) and release the pigments (or mortar and pestle for well, only the best)
    2. Use some sort of alcohol as a solvent (since pigments are much more soluble in alcohols than water)
    3. Set up paper chromatography
    Though this method will really only let you identify the pigments (not really isolating them).

    Again, this is all based off my 'arguably limited' chemistry knowledge. Take with a pinch of salt, but anyway I hope its helped at least a tiny bit.
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    (Original post by Spectral)
    Disclaimer: Completely going off my own knowledge with this and I'm currently an A level student, so feel free to completely disagree with what I write.

    Potassium bromide and Aluminium oxide:
    You mentioned that potassium bromide is soluble whereas aluminium oxide isn't - would make sense therefore to add an (excess of) solvent (water in this case) to dissolve the potassium bromide.
    Dissolving KBr in solution would produce KBr(s) -> K+(aq) + Br-(aq)

    The steps would be:
    1. Add excess water to the sample containing aluminium oxide and potassium bromide
    2. Stir sample (for x number of minutes) in order to homogenise the mixture so that the potassium bromide, that is soluble, dissolves fully.
    3. Get a beaker and place a funnel with filter paper in the funnel and then pour mixture through funnel. This should leave the solid aluminium oxide in the filter paper and the potassium bromide solution should filter through into the beaker.
    4. Not sure what exactly the correct methodology is from here, but what I would say is: wash the aluminium oxide with cold water (to remove any of the solution) and then dry with filter paper. This should leave you with the desired aluminium oxide.
    5. To get back the potassium bromide, just heat the water to evaporate all the water of the solution until what is left is potassium bromide. Again you can then dry this with filter paper to ensure there is no excess water remaining.

    I don't really have time to write in detail the rest of the separations but my ideas are:

    Finding % of aluminium oxide: Probably some sort of acid-base titration is required

    Test for any potassium bromide: Don't know if this allowed (since you'll lose the sample) but the silver nitrate test is the standard test for bromide ions. If this correct, you can go the extra mile and say to use ammonia to distinguish between bromide ions and iodide ions.

    Flammable and non-flammable gas: I would be thinking of fractional distillation, but the flammable and non-flammable part sounds interesting. Perhaps at those temperatures it could lead to a combustion reaction, so use a reducing environment (one with oxygen and other oxidising agents removed)?

    Iodine and sodium nitrate: Sort of similar to the potassium bromide/aluminium oxide separation (maybe even the same). The non-polar solvent is probably something like toluene (methylbenzene (essentially hydrocarbons).

    Pigments in plant leaves: Ok i feel comfortable with this since I'm much better at biology. Essentially:
    1. Blender to break up the plant leaves (cell wall of cells and chloroplast membrane) and release the pigments (or mortar and pestle for well, only the best)
    2. Use some sort of alcohol as a solvent (since pigments are much more soluble in alcohols than water)
    3. Set up paper chromatography
    Though this method will really only let you identify the pigments (not really isolating them).

    Again, this is all based off my 'arguably limited' chemistry knowledge. Take with a pinch of salt, but anyway I hope its helped at least a tiny bit.
    Thank you that is an excellent response with some areas of intrigue. Some of it I have already attended to. I clocked Fractional distillation for the unnamed liquids and chromatography for the Pigments of plant leaves.

    You have definitely provided some interesting suggestions I'll study them thoroughly tomorrow and compare to my coursemates input.

    - regards
    - A-tav
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    Quote:
    "2. Stir sample (for x number of minutes) in order to homogenise the mixture so that the potassium bromide, that is soluble, dissolves fully."

    Would Potassium bromide and aluminium oxide with water added in filtration be a homogeneous or heterogeneous mixture? I'm thinking the latter because of the insolubility of Aluminium oxide. It would remain solid surely as the Potassium bromide dissolved from it. Right?

    I just did a brief search on that.

    Any ideas?
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    Oh I'm sorry, forgot this was a chemistry forum (not biology!).

    I meant homogenous to mean 'to distribute evenly' - essentially its regular, english definition, as opposed to a more precise chemistry definition.

    But yes, you are correct, if we refer to 'homogenous' and 'heterogenous' to refer to in different phases (solid, liquid, gas etc), then definitely it's a heterogenous mixture.

    Again, sorry for the confusion, and yes aluminium oxide if it is indeed insoluble will remain as a solid in the mixture. The potassium bromide should, on the other hand (as it is soluble), remain dissolved in the solution.
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    (Original post by Spectral)
    Oh I'm sorry, forgot this was a chemistry forum (not biology!).

    I meant homogenous to mean 'to distribute evenly' - essentially its regular, english definition, as opposed to a more precise chemistry definition.

    But yes, you are correct, if we refer to 'homogenous' and 'heterogenous' to refer to in different phases (solid, liquid, gas etc), then definitely it's a heterogenous mixture.

    Again, sorry for the confusion, and yes aluminium oxide if it is indeed insoluble will remain as a solid in the mixture. The potassium bromide should, on the other hand (as it is soluble), remain dissolved in the solution.
    Thanks for the reply. Yes don't worry mate. You may be surprised to hear this, but my Bachelor degree choice that my Access course is a prerequisite to. Is a Biology degree. These chemistry units are mandatory though in equivalence to an A level. I'm becoming good at Biochemistry too so hells bells don't denature my enzymes! lol.

    Biology is my first and main degree choice is what I'm saying. I'm over the moon. I have received 4 out of 5 of my choice offers. Just waiting on one. (Slow Uni).
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    QUOTE:

    "2. Briefly describe how you would carry out separations of the following mixtures. Give reasons why you have chosen the method described and include any tests you would carry out to demonstrate the efficiency of the separation (where appropriate)

    (iii) Pigments in plant leaves"

    I've finished my assignment to approximately 90%. For future reference, for anyone else who may come by a similar piece of work. The part mentioned above on demonstrating the efficiency of separation for Chromatography is solved via the use of HPLC - high performance liquid chromatography. HPLC is in common use in a lot of university and industry settings so it is something good to learn about.

    I was actually first introduced to it on a work experience placement, feeling very out of my depth at the time. Now all has become clear!

    Enjoy! Still feel free to keep the thread alive and share your thoughts or perhaps even ask me some questions.

    I don't mind. I do it for Science! :banana::dumbells:
 
 
 
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