The apparatus shown on Figure 11.6, was used to estimate the proportion of oxygen in the atmosphere. A volume of dry air (200 cm³) was passed backwards and forwards over heated copper until no further change in volume took place. The apparatus was then allowed to cool down to room temperature and the final volume reading was then taken. Some typical results are shown below.

Volume of gas before = 200 cm³
Volume of gas after = 157 cm³

During the experiment the copper slowly turned black.

a. Why was the apparatus allowed to cool back to room temperature before the final volume reading was taken?

b. Using the information given above, calculate the percentage volume reduction which has taken place.

c. Explain briefly why there is a change in volume.

d. What observation given above supports your explanation in c? Write a balanced chemical equation for any reaction which has occurred.

e. Give the name of the main residual gas at the end of the experiment.

f. Would you expect the copper to have increased or decreased in mass during the experiment? Explain your answer.

Figure 11.6

Transcribed Image Text:

100 cm of air is pushed out of this syringe into this syringe across hot copper heat air is passed backwards and forwards across the copper, which turns black the volume of air gets smaller and smaller eventually the volume of air stops getting smaller the volume of remaining air is measured heat