Thread: A Reaction

What is the reaction between Sodium Thiosulphate and Hydrochloric Acid. We did it in class as part of a lab to indetify uknown substances, but we never looked at the reaction, because it wasnt really important.

I've done this experiment early on this year in my chemestry unit, but I just had to look it up to make sure I was right. heres the URl for the original source.
http://www.gcsescience.com/rc4.htm

would that be the one your looking for?

Measuring the Rate.


The reaction between sodium thiosulphate solution
and dilute hydrochloric acid.

hydrochloric acid + sodium thiosulphate arrow sodium chloride + sulphur dioxide + sulphur + water.
2HCl(aq) + Na2S2O3(aq) -> 2NaCl(aq) + SO2(g) + S(s) + H2O(l)

The solid sulphur (S(s)) formed in this reaction
makes the colourless solution go cloudy.

The reaction is usually carried out in a flask
placed on a piece of white paper which has a black cross on it.
At the beginning of the reaction, the cross can be seen easily.
As the flask becomes more and more cloudy
the cross gets harder to see.

You can measure the time from the start of the reaction
until the cross can no longer be seen.
This is a way of measuring the rate of formation of sulphur.

The reaction between magnesium and dilute acid
can be followed in a similar way
noting the time taken for the magnesium to disappear.

I guess that would be it, except the sodium thiosulphate was not in a solution. It was solid. It fized and fizzed and fizzed like hell, dissolveing the solid, leaving nothing but a bright yellow liquid.

Alright did it create heat?i have never used it as a solid. were only allowed to use solutions too many irrisponisble people in science. what substances were you trying to identify.

Pierre,

It was not the fizzing that dissolved the solid but the hydrochloric acid. The fizzing was the result of it not the cause. It was provoked by the formation of SO2 (it should have smelled terribly) and the colour is given by sulfur in suspension.

Best regards,

César

Yes, that is true. It smelt terrible. And now that I think about it, it's true that the fizzing did not cause the dissolving, because the crytals themselves weren't fizzing, the actual solution was fizzing.