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    I've been given a homework to do and I've missed the previous lesson explaining about it. I'm stuck on this particular question:

    Q) Some sodium hydroxide solution was added to a solution of substance Q. A white precipitate formed which dissolved when more sodium hydroxide solution was added. Some dilute nitric acid followed by silver nitrate solution was added to a separate solution of Q, and a cream precipitate was formed.

    (a) Name and give the formula of Q.
    (b) Identify the cream precipitate.
    (c) Write an ionic equation for the formation of the cream precipitate.

    From the notes that my friend gave me, Q could be Aluminium (because the white precipitate dissolved in excess sodium hydroxide). However the cream precipitate shows that a Bromide (Br- ) is somewhere in the reaction. Am I right to identify Q as Aluminium Bromide?? :confused: :confused: :confused:

    Please help!! Many thanks in advance
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    Q could also be Zn2+; only distinguished from Al3+ if you do NH3 test
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    (Original post by shengoc)
    Q could also be Zn2+; only distinguished from Al3+ if you do NH3 test
    Thanks a million!

    Also, (if you don't mind me asking...)

    Q)
    • Substance R produced a red flame in a flame test
    • + Sodium hydroxide solution to a solution of R, white insoluble ppt formed
    • A white ppt was formed when dilute HCl followed by BaCl2 solution was added to solution of R


    (a) Name and give the formula of substance R
    (b) Identify the white precipitate

    I thought it could be Strontium Sulphate, but wasn't sure if it gives a white ppt when dissolved in sodium hydroxide
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    (Original post by a rusH)
    Thanks a million!

    Also, (if you don't mind me asking...)

    Q)
    • Substance R produced a red flame in a flame test
    • + Sodium hydroxide solution to a solution of R, white insoluble ppt formed
    • A white ppt was formed when dilute HCl followed by BaCl2 solution was added to solution of R


    (a) Name and give the formula of substance R
    (b) Identify the white precipitate

    I thought it could be Strontium Sulphate, but wasn't sure if it gives a white ppt when dissolved in sodium hydroxide
    when dealing with flame colours, they can be a bit ambiguous in some cases. you are spot on for the sulphate ions being present.

    Sr is not so much smaller than Ba, just one above it. As you might or might not know, calcium sulphate is sparingly soluble and it becomes obvious that group II sulphate solubility decreases down the group - here if you have strontium sulphate, you won't have a solution, you would be having a ppt, if you see what i mean.

    you are most likely to have lithium ion instead.
    http://www.chemguide.co.uk/inorganic...lametests.html
    http://www.chemguide.co.uk/inorganic...olubility.html
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    (Original post by shengoc)
    when dealing with flame colours, they can be a bit ambiguous in some cases. you are spot on for the sulphate ions being present.

    Sr is not so much smaller than Ba, just one above it. As you might or might not know, calcium sulphate is sparingly soluble and it becomes obvious that group II sulphate solubility decreases down the group - here if you have strontium sulphate, you won't have a solution, you would be having a ppt, if you see what i mean.

    you are most likely to have lithium ion instead.
    http://www.chemguide.co.uk/inorganic...lametests.html
    http://www.chemguide.co.uk/inorganic...olubility.html
    Okay it makes a lot more sense now
    Thank you very much, you've been extremely helpful!
 
 
 
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