State the name of the apparatus labelled A in Fig. 1.1.
The student adds a fixed volume and concentration of dilute hydrochloric acid to A, swirls the mixture in A and returns it to the cross. The liquid in the flask gradually turns cloudy. The student measures the time taken for the solution to become so cloudy that the cross can no longer be seen through the mixture. State the name of one piece of apparatus needed that is not shown in Fig. 1.1.
The student repeats the experiment using the same fixed volume and concentration of dilute hydrochloric acid, together with increasing concentrations of aqueous sodium thiosulfate, and draws a fresh cross on paper for each experiment. Explain why drawing a new cross on paper for each experiment reduces the accuracy of the results.
The student then uses the same cross drawn on paper and repeats the experiment with the same fixed volume and concentration of dilute hydrochloric acid and with increasing concentrations of aqueous sodium thiosulfate. Suggest the effect of increasing the concentration of aqueous sodium thiosulfate on the time taken for the cross to become no longer visible.
Sulfur dioxide gas is released in this reaction. Sulfur dioxide causes breathing difficulties in humans. Suggest one precaution necessary in this investigation to avoid breathing difficulties.