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Edexcel - Chemistry Unit 2 - 4 June 2013 watch

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    I dont understand this at all... looked in all my textbooks to work out why this is the answer but no luck... Please help

    The best method of converting ethanol, C2H5OH, into iodoethane, C2H5I, is to
    A heat iodine and ethanol under reflux.
    B react ethanol and potassium iodide in the presence of dilute acid.
    C heat potassium iodide and ethanol with concentrated sulfuric acid.
    D heat red phosphorus, ethanol and iodine under reflux.

    answer is D but whyyy?? I dont understand... how many reactions are we supposedto learn for this exam...
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    So if hydrogen bonding includes N,O and F, which have electronegative values of 3, 3.5 and 4 respectively, why can't chlorine have a hydrogen bond as its value is 3 which is the same as Nitrogen?
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    (Original post by Jayqwe)
    So if hydrogen bonding includes N,O and F, which have electronegative values of 3, 3.5 and 4 respectively, why can't chlorine have a hydrogen bond as its value is 3 which is the same as Nitrogen?
    It has higher shielding and a larger radius and so it doesn't actually distort the bond as much


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    (Original post by posthumus)
    Insanely stupid question.... does the atmosphere count as the environment ?

    I mean would you consider a factory and the atmosphere as being in the same environment.

    Also D won't react with the ozone will it ? only if it had a fluorine atom attached to one of the carbons it would? If so, do we need to know why this is..

    Thanks
    'To make liquid and solid products'. Also they said gaseous products escape into the atmosphere so it can only be B or C. Usually they say allocate a minute per mark in the mcq, but this question would have stumped me.
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    (Original post by Khurc003)
    I dont understand this at all... looked in all my textbooks to work out why this is the answer but no luck... Please help

    The best method of converting ethanol, C2H5OH, into iodoethane, C2H5I, is to
    A heat iodine and ethanol under reflux.
    B react ethanol and potassium iodide in the presence of dilute acid.
    C heat potassium iodide and ethanol with concentrated sulfuric acid.
    D heat red phosphorus, ethanol and iodine under reflux.

    answer is D but whyyy?? I dont understand... how many reactions are we supposedto learn for this exam...
    There are three main ways (I would say two), that we need to know when converting alcohols into haloalkanes. The first is obviously adding KI with an acid.

    The others and arguably easier ways is to add either PX3 or PX5 to the alcohol, in this case it would be PI5, which would replace the hydroxyl group with an halogen atom.
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    (Original post by Khurc003)
    I dont understand this at all... looked in all my textbooks to work out why this is the answer but no luck... Please help

    The best method of converting ethanol, C2H5OH, into iodoethane, C2H5I, is to
    A heat iodine and ethanol under reflux.
    B react ethanol and potassium iodide in the presence of dilute acid.
    C heat potassium iodide and ethanol with concentrated sulfuric acid.
    D heat red phosphorus, ethanol and iodine under reflux.

    answer is D but whyyy?? I dont understand... how many reactions are we supposedto learn for this exam...
    My book says that the way to convert from ethanol to iodoethane is to use PI3 however that can only be made in situ under reflux, In which case the answer would be D.
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    http://www.edexcel.com/migrationdocu...e_20100121.pdf

    For Question 19(ii), I can't seem to figure out the answer, mark scheme says you divide by 2, why do you do this though?
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    an organic compound is found to react with sodium metal and to react with acidified sodium dichromate but not to decolourise bromine wqater, nor to neutralise sodium carbonate solution. the liquid could be:

    A: ethanol
    B: ethane
    C: ethanoic acid
    D: ethene

    the answer is A but why???
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    (Original post by charlieejobson)
    an organic compound is found to react with sodium metal and to react with acidified sodium dichromate but not to decolourise bromine wqater, nor to neutralise sodium carbonate solution. the liquid could be:

    A: ethanol
    B: ethane
    C: ethanoic acid
    D: ethene

    the answer is A but why???
    Well Ethanol react's with sodium metal to give an alkoxide. It also react's with dichromate to give firstly an aldehyde then a carboxylic acid. There is no double bond therefore it wont decolourise bromine water, and it won't neutralise the sodium carbonate because it doesnt have acidic properties.

    It wont be ethane at all
    Ethanoic acid would react with Na2CO3 but wont react with dichromate
    and ethene would decolourise bromine water but wouldn't react with the others
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    (Original post by maryam1996)
    Hi, Can someone please explain to me why chlorofluorocarbons are no longer used as fire retardants and why we use hydrocarbons and why doesn't it break down in the stratosphere?
    Thanks
    -In chlorofluorocarbons, the c-Cl bond can break down in uv light. Once released into the atmosphere I.e. by fire retardants, they can break down, especially high up. When it breaks down you get a chlorine free radical which is EXTREMELY reactive.
    O3/ozone in the atmosphere usually prevents harmful uv from reaching us. Chlorine radicals react with the o3.

    Cl. + O3 ==> ClO. + O2 which then reacts to ClO. + O3==> 2O2 + Cl.

    -As you can see the chlorine radical forms again at the end. Basically it catalyses the decomposition of o3. Although 03 usually breaks down and reforms, the extra radicals make it a net process - the destruction of the ozone, leading to more uv in the atmosphere leading to more cancer etc.

    We now use hydrocarbons to prevent this process, as the bonds won't break down in uv light. Hope this helps!


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    (Original post by HarryMWilliams)
    There are three main ways (I would say two), that we need to know when converting alcohols into haloalkanes. The first is obviously adding KI with an acid.

    The others and arguably easier ways is to add either PX3 or PX5 to the alcohol, in this case it would be PI5, which would replace the hydroxyl group with an halogen atom.
    Thankyou!
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    (Original post by charlieejobson)
    an organic compound is found to react with sodium metal and to react with acidified sodium dichromate but not to decolourise bromine wqater, nor to neutralise sodium carbonate solution. the liquid could be:

    A: ethanol
    B: ethane
    C: ethanoic acid
    D: ethene

    the answer is A but why???
    Hmmm the reason it may be A is, that it matches the description in the question

    Sodium replaces the hydrogen in ethanol (I also believe it reacts pretty violently )

    Dichromate... we know this is used to oxidize alcohols

    Alcohol is not acidic so will not neutralize the very strong base (sodium carbonate)

    I believe bromine goes colorless when it is reduced, so I don't think alcohols do reduce bromine.. let alone react with it ?

    Could someone confirm this one please

    I know alkenes definitely react with bromine ... to produce Br- ions
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    (Original post by Polish master)
    Well Ethanol react's with sodium metal to give an alkoxide. It also react's with dichromate to give firstly an aldehyde then a carboxylic acid. There is no double bond therefore it wont decolourise bromine water, and it won't neutralise the sodium carbonate because it doesnt have acidic properties.

    It wont be ethane at all
    Ethanoic acid would react with Na2CO3 but wont react with dichromate
    and ethene would decolourise bromine water but wouldn't react with the others
    thats a nice explanation but Im a little confused with it not decolourising bromine water, because isnt there a double bond in a carboxylic acid? :confused:

    Also, why cant it be ethane?
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    (Original post by Khurc003)
    thats a nice explanation but Im a little confused with it not decolourising bromine water, because isnt there a double bond in a carboxylic acid? :confused:

    Also, why cant it be ethane?
    The bromine test is usually used to detect a C=C bond. Not used for every double bond ever because it wouldn't be a great test seeing as there are so many molecules with double bonds so if each one declourised bromine water then you still wouldnt be any closer to working out a specific molecule haha. The best way to test for a carboxylic acid group is to add a carbonate.
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    (Original post by Polish master)
    The bromine test is usually used to detect a C=C bond. Not used for every double bond ever because it wouldn't be a great test seeing as there are so many molecules with double bonds so if each one declourised bromine water then you still wouldnt be any closer to working out a specific molecule haha. The best way to test for a carboxylic acid group is to add a carbonate.
    That makes sense... thanks!
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    (Original post by Khurc003)
    thats a nice explanation but Im a little confused with it not decolourising bromine water, because isnt there a double bond in a carboxylic acid? :confused:

    Also, why cant it be ethane?
    You'll learn at A2 that the C=O double bond in carboxylic acids is not as electron dense to react with the bromine.

    Also ethane does not react with sodium carbonate as it's not acidic.

    I believe it also does not react with sodium... it's not very reactive.
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    (Original post by Polish master)
    Well Ethanol react's with sodium metal to give an alkoxide. It also react's with dichromate to give firstly an aldehyde then a carboxylic acid. There is no double bond therefore it wont decolourise bromine water, and it won't neutralise the sodium carbonate because it doesnt have acidic properties.

    It wont be ethane at all
    Ethanoic acid would react with Na2CO3 but wont react with dichromate
    and ethene would decolourise bromine water but wouldn't react with the others
    thank you so much, you're a star!
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    (Original post by posthumus)
    You'll learn at A2 that the C=O double bond in carboxylic acids is not as electron dense to react with the bromine.

    Also ethane does not react with sodium carbonate as it's not acidic.

    I believe it also does not react with sodium... it's not very reactive.
    Thanks with the double bond part!
    ermm... but the question says it doesnt react with sodium carbonate.... so i still dont understand why it cant be ethane
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    (Original post by Khurc003)
    Thanks with the double bond part!
    ermm... but the question says it doesnt react with sodium carbonate.... so i still dont understand why it cant be ethane
    Like I said, ethane is not acidic

    Sodium carbonate is a very strong base which reacts with acids

    H+ will not be liberated from ethane.

    Na2CO3 + 2H+ -----> 2Na^+ + CO2 + H2O
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    Can anyone explain a condensation reaction with an example? That is one reaction I cant understand :/
 
 
 
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