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    The reaction between Na2S2O3 and HCl is described as 'acid catalysed' but is HCl a catalyst?
    I don't think it is. Do you?
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    Increasing the acid concentration increases the rate, so yes it is.

    When you measure the reaction, you're measuring the rate of precipitate formation, and that precipitate is elemental sulfur (S8) - which is formed by the intermediate HS2O3-- so what would be the equation for the formation of that in the thiosulfate-acid mixture?
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    (Original post by Aclarke55)
    The reaction between Na2S2O3 and HCl is described as 'acid catalysed' but is HCl a catalyst?
    I don't think it is. Do you?
    Na2S2O3 + 2HCl -> 2NaCl + S + SO2

    A catalyst speeds up a reaction without getting used up.

    It is not a catalyst.

    Also, at very high concentrations, the rate is unaffected by the concentration of the acid, i.e. it doesn't even speed the reaction up.
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    (Original post by Stiff Little Fingers)
    Increasing the acid concentration increases the rate, so yes it is.
    Not like I like arguing with people with more qualifications than I do, but no it isn't.
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    (Original post by Pigster)
    Not like I like arguing with people with more qualifications than I do, but no it isn't.
    Fair enough - I was focusing more on the effect it has on rate since that's what the acid catalysed refers to, but in terms of terminology you're right.

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