A 100 cm³ sample of air is passed repeatedly over heated copper using two gas syringes until no further change occurs. The final volume of gas is 79 cm³. Wh...
Question 1 Report
A 100 cm³ sample of air is passed repeatedly over heated copper using two gas syringes until no further change occurs. The final volume of gas is 79 cm³. Which gas has been removed by the copper?
Answer Details
Hot copper reacts with oxygen only: 2Cu + O2 → 2CuO, and the black copper(II) oxide stays behind as a solid, so that gas is removed from the air being pushed to and fro between the syringes.
The volume falls from 100 cm3 to 79 cm3, a drop of 21 cm3. That is 21% of the original sample, which matches the proportion of oxygen in air exactly. Nitrogen is the wrong choice because 79 cm3 is what remains rather than what was lost, and nitrogen is far too unreactive to combine with copper. Carbon dioxide and argon are present at only about 0.04% and 0.9%, far too little to explain a 21 cm3 change. Subtract to find the gas used.
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