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Edexcel - Chemistry Unit 2 - 4 June 2013 Watch

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    (Original post by jod.14)
    Hello, can anyone explain this question to me:

    A solid gives a red colour in a flame test and reacts with concentrated sulfuric acid to produce steamy fumes, but no other gases. The solid could be:

    A) lithium bromide
    B) strontium chloride
    C) calcium bromide
    D) sodium chloride

    please help! stressing out!
    B.

    Strontium ion gives a red/crimson colored flame. With concentrated H2SO4, HCL forms which reacts with moisture in air to give steamy white fumes.
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    Guys thanks a lot for all the help on reflux apparatus.

    Another question, can there be permanent dipole-dipole interactions between molecules which have polar bonds but no overall dipole, like CCl4?
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    (Original post by posthumus)
    I think it's four, but in liquids it's fewer than that... I'd go with 2. But I haven't come across a question where that knowledge is required, have you ??
    Haven't come across any yet. But, you never know. It might come tomorrow. :eek:
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    How do you work out if a molecule is polar or not??!!
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    For a titration question, how can you tell if an alkali or acid is being added? I can never tell and guess :/
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    (Original post by MSamuel)
    i need somewhere to vent my anger so im choosing student room.
    i just did a past paper i hadn't done before to see how it went, i made so many stupid bloody mistakes - i never read the question properly - and i lost a good 7 marks. this put me down to a B one off an A.
    im so angry at myself, just thought i'd share it with you guys.
    any tips on how to help me? apart from the damn obvious "read the question more carefully", none of that please or ill screw at you.
    thank you.
    :hugs: :grouphugs:

    I think apart from exam technique, it could be other factors that might be leading to you losing concentration perhaps

    My advice would be to drink plenty of water, before and during the exam tomorrow. Water helps alot, it helps to really clear your mind and focus well. Also try and have some fruits if you can. A banana and an apple is good :yy:. Don't over do the revision tomorrow, because it will only stress you up even more. Take things steady and make sure you get plenty of sleep for tomorrow (even if the exam is in the afternoon).

    Best of luck and pm me if you wanna speak about your problems!
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    (Original post by GCSE-help)
    Guys thanks a lot for all the help on reflux apparatus.

    Another question, can there be permanent dipole-dipole interactions between molecules which have polar bonds but no overall dipole, like CCl4?
    Nice question. I guess there won't be any. Just stronger instantaneous dipole-induced dipole (london force) attraction.
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    (Original post by GCSE-help)
    Guys thanks a lot for all the help on reflux apparatus.

    Another question, can there be permanent dipole-dipole interactions between molecules which have polar bonds but no overall dipole, like CCl4?
    No


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    (Original post by Jayqwe)
    For a titration question, how can you tell if an alkali or acid is being added? I can never tell and guess :/
    The solution to which you add the other solution is always in the conical flask.
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    (Original post by airheadbuster)
    Nice question. I guess there won't be any. Just stronger instantaneous dipole-induced dipole (london force) attraction.
    The electronegativity difference won't make London forces any stronger I think. It's only about the number of electrons.


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    Tertiary halogenoalkanes are the most stable but most reactive....?

    how does this make sense? Surely it contradicts itself.
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    (Original post by kevsamuel)
    Tertiary halogenoalkanes are the most stable but most reactive....?

    how does this make sense? Surely it contradicts itself.
    Tertiary carbocations are most stable. Tertiary halogenoalkanes are indeed most reactive.
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    Is the organic layer or aqueous layer denser when you're preparing a halogenoalkane?! The text book and revision guide say the opposite >.<
    Also summary of which apparatus for which reactions would be amazing- another textbook contradiction x
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    Wait, if you lose 7 marks you get a B? Whoa I thought the boundary was lower than that o__o
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    (Original post by kevsamuel)
    Tertiary halogenoalkanes are the most stable but most reactive....?

    how does this make sense? Surely it contradicts itself.
    Because they're more stable they're more likely to form therefore most reactive that make sense?
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    (Original post by airheadbuster)
    Trust me, you need to feel it or else you won't improve. I felt it and that's what made me a consistent guy.

    I hope I will thank you for your support xx
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    (Original post by Juliajuliajulia)
    Is the organic layer or aqueous layer denser when you're preparing a halogenoalkane?! The text book and revision guide say the opposite >.<
    Also summary of which apparatus for which reactions would be amazing- another textbook contradiction x
    Because the organic layer has more substances dissolved in it which makes it denser.
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    (Original post by airheadbuster)
    Tertiary carbocations are most stable. Tertiary halogenoalkanes are indeed most reactive.
    Okay thanks But I'm still unsure what you mean by tertiary carbocations?
    Wouldn't that just be a tertiary halogenoalkane/alcohol?
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    (Original post by kevsamuel)
    Tertiary halogenoalkanes are the most stable but most reactive....?

    how does this make sense? Surely it contradicts itself.
    **The tertiary carbocation formed during nucleophilic substitution is more stable than a secondary or primary carbocation**
    Tertiary halogenoalkanes are more reactive, because the stable tertiary carbocation is formed as an intermediate.

    A tertiary carbocation is an ion containing a positively charged carbon atom that is covalently bonded to three other carbon atoms.
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    (Original post by Juliajuliajulia)
    Is the organic layer or aqueous layer denser when you're preparing a halogenoalkane?! The text book and revision guide say the opposite >.<
    Also summary of which apparatus for which reactions would be amazing- another textbook contradiction x
    Usually they tell you the density of the organic layer in the question. Then you compare it to 1.00 g/cm3

    Can you name some reactions for which you want to know the apparatus?
 
 
 
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