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Aluminium and Barium Nitrate reaction

  1. Oct 28, 2015 #1
    1. The problem statement, all variables and given/known data

    2. Relevant equations

    3. The attempt at a solution
    I chose B, because I thought adding more OH- would cause the reaction to shift to the left, and a low temperature would slow the rate of reaction, but the answer is A, why pH 7?
  2. jcsd
  3. Oct 28, 2015 #2


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    Staff: Mentor

    Think what keeps aluminum powder relatively stable. Despite Al being highly reactive even in powdered form it doesn't react vigorously with the air oxygen. Why?

    Next step is to think how this lowered reactivity survives in neutral, acidic and caustic solutions.
  4. Oct 28, 2015 #3
    Aluminium forms a layer of oxide which makes it unreactive. It is an amphoteric oxide so it reacts with acids and bases, but it doesn't react with water, so aluminium will stay unchanged. Thanks I think I've understood
  5. Oct 29, 2015 #4


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    I am not sure what this explanation really is if you were to make it more explicit. It is not an easy question.
    However I would be inclined to an explanation involving the protonation of the aluminium hydroxide and protonation and volatility effects on ammonia.
    Last edited: Nov 1, 2015
  6. Oct 31, 2015 #5
    Oh I see..thanks
  7. Nov 1, 2015 #6


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    I should have said aluminium hydroxide. I am not sure you can be expected to know - I suspected, but had to look up, that this gets deprotonated going from pH 7 to 14. You can be expected to know or to be learning at this time that ammonium is essentially protonated at pH 7 (exists as ammonium ion) and not protonated (exists as NH3) at pH 14, and to relate this to any laboratory frequentation from which you may know that ammonia smells like hell and ammonium salts not, or not very.

    I think it is all very well for them to tell you it's at pH 7 or 14. You may feel slightly left in the air. If it is at one pH or another something is making it so. You may wonder.
    Last edited: Nov 1, 2015
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