When aqueous sodium thiosulfate is combined with dilute hydrochloric acid, insoluble sulfur forms as a precipitate. This causes the mixture to become hard to see through.
$\text{Na}_2\text{S}_2\text{O}_3(aq) + 2\text{HCl}(aq) \rightarrow \text{S}(s) + 2\text{NaCl}(aq) + \text{H}_2\text{O}(l) + \text{SO}_2(g)$
The length of time for the cross to vanish from sight is measured.
(a)[1]
State the sequence in which the aqueous sodium thiosulfate, hydrochloric acid and distilled water ought to be added to the flask.
(b(i))[2]
Complete the table to show the volumes that should be used and the predicted time for the cross to disappear from sight in experiment 3.
(b(ii))[2]
Use collision theory to explain why increasing the concentration of sodium thiosulfate would change the rate of reaction.
(c)[3]
Use collision theory to explain why the rate of reaction would increase.
Worked solution & mark scheme
This 8-mark question has a full step-by-step worked solution and mark scheme. One marking point: “Correct sequence for adding Na₂S₂O₃, H₂O and HCl (any valid sequence shown)” …