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Sodium thiosulphate and hydrochloric acid

The reaction between Na2S2O3 and HCl is described as 'acid catalysed' but is HCl a catalyst?
I don't think it is. Do you?
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?
Reply 2
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.
Reply 3
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.
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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