200 cm3 of air was passed over heated copper in a syringe several times to produce copper (II) oxide. When cooled, the final volume of air recorded was 158c...

To estimate the percentage of oxygen in the air, we need to use the fact that copper (II) oxide is formed by the reaction of copper and oxygen in the air. The volume of air decreases as the oxygen is used up in the reaction, so the difference between the initial and final volume of air can be used to estimate the volume of oxygen that reacted with the copper. First, let's calculate the difference in volume of air before and after the reaction: Initial volume of air = 200 cm³ Final volume of air = 158 cm³ Difference in volume = 200 cm³ - 158 cm³ = 42 cm³ Next, we need to assume that the copper reacted completely with the oxygen in the air, which means that all the oxygen in the initial volume of air is accounted for in the difference in volume. This allows us to calculate the percentage of oxygen in the air as follows: Volume of oxygen = Difference in volume = 42 cm³ Total volume of air = Initial volume of air = 200 cm³ Percentage of oxygen in the air = (Volume of oxygen / Total volume of air) x 100 = (42 cm³ / 200 cm³) x 100 = 21% Therefore, the percentage of oxygen in the air is estimated to be 21%.