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OCR AS - Chemistry Unit F322 - Chains, energy and resource - REVISION! watch

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    (Original post by J DOT A)
    Wth? we don't need to know that?

    Describe the rate of hydrolysis of a halogenalkane... with a Cl-, Br- and I- attached to butane molocule. .

    Also, list the conditions needed for the hydrolysis of a halogenalkane. What acts as a nucleophile and a solvent, and suggest why you need to use a solvent.

    Ethanol solvent, h20 nucleophile (the OH bit) AgNO3.

    Not sure what conditions. heat maybe

    Is the solvent used to bring the AgNO3 and halagenoalkane together?
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    (Original post by viksta1000)
    technically, the question didn't really ask for a type of isomer

    but thanks!
    so it didnt specify but you defined stereo lol
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    I dont understand anything at all about modern analytical techniques if anyone could help?:/
    quote me if you reply
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    (Original post by 000015080)
    I dont understand anything at all about modern analytical techniques if anyone could help?:/
    quote me if you reply
    infrared and mass spec?
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    (Original post by 000015080)
    I dont understand anything at all about modern analytical techniques if anyone could help?:/
    quote me if you reply
    what do you need to know?
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    (Original post by Joseppea)
    X
    When asked for the reagent for the oxidation of alcohols, have you been taught to put "K2Cr2O7", Acidified dichromate ions or Cr2O7 2-
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    (Original post by 000015080)
    I dont understand anything at all about modern analytical techniques if anyone could help?:/
    quote me if you reply
    What are you stuck on?

    IR, just look at the data sheet. Mass spec, look at the last line for the Mr and peaks for possible fragments.
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    (Original post by chemkid)
    infrared and mass spec?
    yehh dont understand any of it :/
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    (Original post by SteveCrain)
    what do you need to know?
    everything
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    Can some one share his chemistry revision notes?
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    (Original post by 000015080)
    yehh dont understand any of it :/
    Infrared you just need to know how the analyze the spectra. To do this you use the data sheet given to you... on the back it has a list of the characteristic infrared absorptions.
    On the spectrum there'll be some peaks (even though they look like troughs, they're called peaks!). Most of them are irrelevant, what you're looking for are the ones with the least transmittance (y axis) so basically the longest of the peaks.
    Read off the x-axis where these peaks are then compare with the wave number on the data sheet to find out which bond it is.
    You may find it helps to annotate the spectrum or even turn it upside down (some people find this helpful:rolleyes:)
    So an example... if there was a peak at 1200cm^-1 then this would indicate a C-O bond so the molecule could be either an alcohol, ester or carboxylic acid. Then if there's a very broad peak between 2500-3300cm^-1 then it's a carboxylic acid.
    Hopefully this'll make sense when you look at the data sheet/an example

    Mass Spectrometry you need to know how it works and how to analyze the spectra.
    How it works - basically just the order everything happens in so vapourisation, ionisation, acceleration, deflection, detection (might help to remember it as Victor Is A Daft Duck )
    How to analyze - the spectra are give as bar graph type things where the y axis is relative abundance and the x axis is the m/z ratio (mass to charge). For AS the charge is always going to be +1 so the x axis is basically the mass.
    If the spectrum is of a molecule then the peak the furthest to the right is the M+ peak which is the ion formed by the molecule (e.g. if the molecule was CH4 the M+ peak would be the ion CH4 +) so this will give you the Mr of the molecule. There may be a small peak to the right of this which is only because of the presence of carbon-13 so ignore that
    The other peaks are formed because after ionisation the bonds are vibrating so fragmentation occurs where bits of the molecule break off and form their own ions.
    Fragment ions can only form from sections of the molecule
    e.g.
    H-C-C-C-H is the molecule, so you can get a fragment ion of H-C but not H-C-C-H

    so basically the fragment ion forms when one or more of the bonds within the original ion break. So if you analyze the spectrum fully, you'd be able to work out the structure from where the peaks occur.

    The base peak (one with relative abundance of 100) is the fragment ion that is either the most stable and therefore the most likely to form OR there are just loads of ways of producing it. The other peaks are given relative to this.

    If you're given a spectrum of an element, it will show all of the isotopes. This type of spectrum is much easier to analyze... the one with the highest relative abundance is the most abundant isotope so it's pretty straight forward
    They may ask you to work out the relative atomic mass from it in which case you simply read off the values from axes

    Hope this helps and good luck with your revision. You can always ask if you need help with anything else
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    (Original post by jaez121)
    Can some one share his chemistry revision notes?
    Hope they help if you want more pm me
    Attached Files
  1. File Type: doc as test 7 notes - basic concepts.doc (84.5 KB, 166 views)
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    (Original post by chemkid)
    Infrared you just need to know how the analyze the spectra. To do this you use the data sheet given to you... on the back it has a list of the characteristic infrared absorptions.
    On the spectrum there'll be some peaks (even though they look like troughs, they're called peaks!). Most of them are irrelevant, what you're looking for are the ones with the least transmittance (y axis) so basically the longest of the peaks.
    Read off the x-axis where these peaks are then compare with the wave number on the data sheet to find out which bond it is.
    You may find it helps to annotate the spectrum or even turn it upside down (some people find this helpful:rolleyes:)
    So an example... if there was a peak at 1200cm^-1 then this would indicate a C-O bond so the molecule could be either an alcohol, ester or carboxylic acid. Then if there's a very broad peak between 2500-3300cm^-1 then it's a carboxylic acid.
    Hopefully this'll make sense when you look at the data sheet/an example

    Mass Spectrometry you need to know how it works and how to analyze the spectra.
    How it works - basically just the order everything happens in so vapourisation, ionisation, acceleration, deflection, detection (might help to remember it as Victor Is A Daft Duck )
    How to analyze - the spectra are give as bar graph type things where the y axis is relative abundance and the x axis is the m/z ratio (mass to charge). For AS the charge is always going to be +1 so the x axis is basically the mass.
    If the spectrum is of a molecule then the peak the furthest to the right is the M+ peak which is the ion formed by the molecule (e.g. if the molecule was CH4 the M+ peak would be the ion CH4 +) so this will give you the Mr of the molecule. There may be a small peak to the right of this which is only because of the presence of carbon-13 so ignore that
    The other peaks are formed because after ionisation the bonds are vibrating so fragmentation occurs where bits of the molecule break off and form their own ions.
    Fragment ions can only form from sections of the molecule
    e.g.
    H-C-C-C-H is the molecule, so you can get a fragment ion of H-C but not H-C-C-H

    so basically the fragment ion forms when one or more of the bonds within the original ion break. So if you analyze the spectrum fully, you'd be able to work out the structure from where the peaks occur.

    The base peak (one with relative abundance of 100) is the fragment ion that is either the most stable and therefore the most likely to form OR there are just loads of ways of producing it. The other peaks are given relative to this.

    If you're given a spectrum of an element, it will show all of the isotopes. This type of spectrum is much easier to analyze... the one with the highest relative abundance is the most abundant isotope so it's pretty straight forward
    They may ask you to work out the relative atomic mass from it in which case you simply read off the values from axes

    Hope this helps and good luck with your revision. You can always ask if you need help with anything else
    Thank you so much, some people are so helpful thanks alot!! And is it ok if i PM you if i'm stuck on anything else?
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    (Original post by 000015080)
    Thank you so much, some people are so helpful thanks alot!! And is it ok if i PM you if i'm stuck on anything else?
    No worries Of course! I'm always happy to help... plus it helps me find out if I actually know what I've learnt
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    Can someone explain to me how to draw stereoisomers, I always get confused with this.

    Also Hess cycles.. thank you
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    (Original post by Bright)
    Can someone explain to me how to draw stereoisomers, I always get confused with this.

    Also Hess cycles.. thank you
    stereoisomers? all its asking you to realise is that the c=c bond in an alkene restricts movement due to the sideways overlap of p orbitals, above and below the plane of the carbon atoms. Carbon forms 4 covalent bonds so you start by drawing the c=c, then have the two groups branching from either carbon.

    Hess cycles are a bit tricky if you dont know how to do them, can you explain what exactly you don't understand about them?
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    (Original post by hockeyjoe)
    stereoisomers? all its asking you to realise is that the c=c bond in an alkene restricts movement due to the sideways overlap of p orbitals, above and below the plane of the carbon atoms. Carbon forms 4 covalent bonds so you start by drawing the c=c, then have the two groups branching from either carbon.

    Hess cycles are a bit tricky if you dont know how to do them, can you explain what exactly you don't understand about them?
    Umm yeah I get that but sometimes I get confused when they tell me to draw different isomers or something.. I guess I just need to revise it and I'll understand.

    Hess Cycles, it's mainly constructing the hess cycles, I mean I know combustion the arrows point down and vice versa for formation but sometimes I get confused when putting the numbers down if you get what I mean?
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    (Original post by Bright)
    Umm yeah I get that but sometimes I get confused when they tell me to draw different isomers or something.. I guess I just need to revise it and I'll understand.

    Hess Cycles, it's mainly constructing the hess cycles, I mean I know combustion the arrows point down and vice versa for formation but sometimes I get confused when putting the numbers down if you get what I mean?
    Yer the arrows do point down for combustion and up for formation your right, however you have to make sure the arrows are always gonig from the reactants to the products, in an anticlockwise kind of motion? so say for example you values for enthalpy of formation pointing upwards towards your reactants, and these numbers were positive, you'd have to change the values to negative as the arrows have to be going towards the products? does that make sense? Also, you have to use the big numbers in front of the molecules to work out how much enthalpy there is, like for example if you have a combustion of methane, CH4, and the value was +89 or whatever, then this value only works for one molecule of CH4, if there are say 8 molecules of CH4, you have to multiply the enthalpy values accordingly?
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    (Original post by hockeyjoe)
    Yer the arrows do point down for combustion and up for formation your right, however you have to make sure the arrows are always gonig from the reactants to the products, in an anticlockwise kind of motion? so say for example you values for enthalpy of formation pointing upwards towards your reactants, and these numbers were positive, you'd have to change the values to negative as the arrows have to be going towards the products? does that make sense? Also, you have to use the big numbers in front of the molecules to work out how much enthalpy there is, like for example if you have a combustion of methane, CH4, and the value was +89 or whatever, then this value only works for one molecule of CH4, if there are say 8 molecules of CH4, you have to multiply the enthalpy values accordingly?
    Yep I get all of that. Ok maybe I do get enthalpy? lol

    Thanks
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    I find this site quite helpful: http://www.chemguide.co.uk
 
 
 
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