Rates of Reaction

Measuring the Rate.

2) The reaction between sodium thiosulfate solution
and dilute hydrochloric acid.

HCl + sodium thiosulfate sodium chloride + sulfur dioxide + sulfur + water.
HCl_(aq)    +   Na₂S₂O_3(aq)              NaCl_(aq)       +     SO_2(g)       +       S_(s)  +  H₂O_(l)

The solid sulfur (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 sulfur.

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

See increasing the concentration.

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