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Edexcel - Chemistry Unit 2 - 4 June 2013 watch

  • View Poll Results: Which topic(s) are you finding most difficult?
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    (Original post by marseille_h)
    A short question : Why does H20 have a higher boiling point than : HF, NH3 , and CH4 ?

    Thanks
    H20 forms 2 hydrogen bonds per molecule, whereas NH3 and HF only form one H bond per molecule. CH4 only has London forces.
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    (Original post by marseille_h)
    A short question : Why does H20 have a higher boiling point than : HF, NH3 , and CH4 ?

    Thanks
    water has two delta+ hydrogen and so can from two hydrogen bonds per molecule, the others can only form one
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    (Original post by marseille_h)
    A short question : Why does H20 have a higher boiling point than : HF, NH3 , and CH4 ?

    Thanks
    I guess NH3 can only form one hydrogen bond then It seems only water is mentioned to have 2

    HF only one hydrogen bond also

    CH4, not hydrogens bonds... london forces only - which are much weaker
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    Guys I know halogenoalkanes are not soluble in water because they cannot form Hydrogen bonds with Water molecules. However, can't fluoroalkanes dissolve in water due the H from the water molecule bonding with the F in the haloalkane?
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    (Original post by posthumus)
    I guess NH3 can only form one hydrogen bond then It seems only water is mentioned to have 2

    HF only one hydrogen bond also

    CH4, not hydrogens bonds... london forces only - which are much weaker
    Yeah so it must be something to do with lone pairs Haha worked that out using the past papers
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    Thats what I put but I just wanted to know a modal answer in case a question in section B or C comes up thanks
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    (Original post by airheadbuster)
    Attachment 222975

    Here's another better one.

    @GCSE, there are two hydrogen in a molecule of water. So, there will be two hydrogen bonding per molecule.
    all group one and two salts are white
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    (Original post by GCSE-help)
    Yeah so it must be something to do with lone pairs Haha worked that out using the past papers
    Yes it must be something to do with the lone pairs, not the number of hydrogen's like some other people are saying as that would mean 3 for NH3 not the one (which must be due to its singular lone pair compared to the two lone pairs on oxygen in H20)
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    guys, what time is this exam?
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    (Original post by study beats)
    guys, what time is this exam?
    13h30 !
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    (Original post by Goods)
    all group one and two salts are white
    Hey goods could you explain to me why beryllium is so unreactive ? [possibly with reference to BeO layer]

    also any observations to be made about the group 2 oxides, are they white too solids too ?
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    Does anyone know if the indicators are specific for certain types of chemicals ???
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    (Original post by marseille_h)
    13h30 !
    oh its the afternoon exam...thats why i see this guy next to me revising chemistry lol......GOOD LUCK PEEPS!
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    Guys are fluoroalkanes soluble in water?
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    Name:  ImageUploadedByStudent Room1370334544.089486.jpg
Views: 159
Size:  147.8 KB

    Why don't you doubt the 0.06 seeing as it is plus or minus?

    Answer is c
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    (Original post by GCSE-help)
    Guys are fluoroalkanes soluble in water?
    No the h bonds they form with water aren't strong enough


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    (Original post by bhowland1994)
    Yes it must be something to do with the lone pairs, not the number of hydrogen's like some other people are saying as that would mean 3 for NH3 not the one (which must be due to its singular lone pair compared to the two lone pairs on oxygen in H20)
    Thanks!
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    (Original post by GCSE-help)
    Guys I know halogenoalkanes are not soluble in water because they cannot form Hydrogen bonds with Water molecules. However, can't fluoroalkanes dissolve in water due the H from the water molecule bonding with the F in the haloalkane?
    I better leave now. This question got me confused big time.
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    (Original post by Matterhorn)
    No the h bonds they form with water aren't strong enough


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    They don't even form H bonds at all. Fluoroalkanes cannot hydrogen bond.
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    (Original post by Matterhorn)
    Name:  ImageUploadedByStudent Room1370334544.089486.jpg
Views: 159
Size:  147.8 KB

    Why don't you doubt the 0.06 seeing as it is plus or minus?

    Answer is c
    Yes, the overall percentage error would be 0.48%, however look at the answers; the answers already have the +/- sign, so you don't have to double it because the +/- is already accounted for. Make sense?
 
 
 
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