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Chemistry Unit 2 Edexcel, Exam- 23rd May 2012

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    (Original post by Arusa01)
    HAA! Princess?
    Princess jajajajaja
    Yolo
    LOL Scrib
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    (Original post by Future Medics)
    Princess jajajajaja
    Yolo
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    PM
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    Hey, how would u know if you need to use silver nitrate or hexane if u want to test halogen/halide?
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    why does NH3 have a lower boiling point than HF and H2O have a higher boiling point than HF? Help, someone!!
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    (Original post by VRS)
    Explain why the thermal stability increases with nitrates and carbonated down group 1 and 2

    Also what are the trends we have to know for group 1,2,7 and across the period? Just trends


    This was posted from The Student Room's iPhone/iPad App
    from group 1 NaC03 downwards ,the carbonates don't decompose when heated
    only the nitrates of group 1 from Na downwards decompose
    so the thermal stability increases down group 2 meaning the carbonates and nitrates become more stable to heat as the ionic radius of the positive ion increases down the group ie the positive ion becomes larger so polarisation of the carbonated electron cloud

    i think the only trends you need to know are :
    solubility of group 2 hydroxides and sulfates
    thermal stabilities of group 1 and 2
    and with group 7 there isnt a trend you need to learn except that the ionization energy decrease and the electro negativity also decreases down the group
    the main things you need to know about group 7 are its reactions
    and the test for halides
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    also someone explain steric inheritance!!
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    (Original post by Pandamojia)
    Hey, how would u know if you need to use silver nitrate or hexane if u want to test halogen/halide?
    Silver Nitrate for Chloride, Bromide, Iodide ions
    Hexane for Chlorine, Bromine, Iodine
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    (Original post by Arusa01)
    HAA! Princess?
    lol.
    meant bride. what your name means in arabic.
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    (Original post by Exams v__v)
    why does NH3 have a lower boiling point than HF and H2O have a higher boiling point than HF? Help, someone!!
    as HF can form hydrogen bonding so more energy needed and H2O has greater b.p then HF as it can from up to 2 hydrogen bonds with one molecule so much stronger
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    (Original post by fiza_1)
    as HF can form hydrogen bonding so more energy needed and H2O has greater b.p then HF as it can from up to 2 hydrogen bonds with one molecule so much stronger
    Even NH3 can form H.B, but still why is it's boiling point lower than that of HF?
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    (Original post by Exams v__v)
    why does NH3 have a lower boiling point than HF and H2O have a higher boiling point than HF? Help, someone!!
    H2O has a higher boiling point than HF because it can form 2 hydrogen bonds as there are 2 electron lone pairs on the oxygen while HF forms 1 hydrogen bond. So more energy required to break the intermolecular forces in H2O than in HF.

    Not sure about why NH3 has a lower boiling point than HF
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    (Original post by The Doggfather)
    Silver Nitrate for Chloride, Bromide, Iodide ions
    Hexane for Chlorine, Bromine, Iodine
    Yh but isn't it Chlorine from CH3CH2CH2Cl an atom? Yet...we used silver nitrate?
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    (Original post by fiza_1)
    from group 1 NaC03 downwards ,the carbonates don't decompose when heated
    only the nitrates of group 1 from Na downwards decompose
    so the thermal stability increases down group 2 meaning the carbonates and nitrates become more stable to heat as the ionic radius of the positive ion increases down the group ie the positive ion becomes larger so polarisation of the carbonated electron cloud

    i think the only trends you need to know are :
    solubility of group 2 hydroxides and sulfates
    thermal stabilities of group 1 and 2
    and with group 7 there isnt a trend you need to learn except that the ionization energy decrease and the electro negativity also decreases down the group
    the main things you need to know about group 7 are its reactions
    and the test for halides
    Thank you so much - appreciate it!


    This was posted from The Student Room's iPhone/iPad App
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    (Original post by The Doggfather)
    H2O has a higher boiling point than HF because it can form 2 hydrogen bonds as there are 2 electron lone pairs on the oxygen while HF forms 1 hydrogen bond. So more energy required to break the intermolecular forces in H2O than in HF.

    Not sure about why NH3 has a lower boiling point than HF
    Cant the delta positive 2 hydrogens also form hydrogen bonds? So in all, 4 hydrogen bonds in water molecules?
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    (Original post by Exams v__v)
    Even NH3 can form H.B, but still why is it's boiling point lower than that of HF?
    as HF has higher electro negativity
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    Cant the delta positive 2 hydrogens in water molecule also form hydrogen bonds? So in all, 4 hydrogen bonds in water molecules?
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    (Original post by Pandamojia)
    And how would u know to use hexane or silver nitrate to test halide?
    Add Silver Nitrate and Dilute Nitric Acid
    Chloride - White ppt
    Bromide - Cream ppt
    Iodide - Yellow ppt

    In Hexane
    Chlorine - Colourless
    Bromine - Orange-Red
    Iodine - Pink-Violet

    In Water
    Chlorine - Colourless
    Bromine - Yellow-Orange
    Iodine - Brown

    If the Halogen is not bonded to another atom, then add to Hexane or Water. Otherwise add Silver Nitrate and Dilute Nitric acid e.g. KCl, KBr
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    (Original post by Exams v__v)
    Cant the delta positive 2 hydrogens in water molecule also form hydrogen bonds? So in all, 4 hydrogen bonds in water molecules?
    They can form hydrogen bonds with the oxygen on another water molecule but that's the same as when the oxygen forms hydrogen bonds with hydrogen's if you know what I mean. So don't include them, it's 2 hydrogen bonds per water molecule because of 2 electron lone pairs.
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    (Original post by Exams v__v)
    Cant the delta positive 2 hydrogens in water molecule also form hydrogen bonds? So in all, 4 hydrogen bonds in water molecules?
    In H2O the O only has 2 pair of lone electrons so only 2 hydrogen bonds can occur.
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    (Original post by The Doggfather)
    They can form hydrogen bonds with the oxygen on another water molecule but that's the same as when the oxygen forms hydrogen bonds with hydrogen's if you know what I mean. So don't include them, it's 2 hydrogen bonds per water molecule because of 2 electron lone pairs.
    Thank you so much.

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