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Tracking Oxygen in a Copper Pigment Model 4 questions
Tracking Oxygen in a Copper Pigment Model
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A ceramics class studies a model of copper oxide pigment. An initial solid contains copper(I) oxide, Cu2O. When the solid takes up oxygen from the air, it can become copper(II) oxide, CuO. The model assumes that no copper leaves and that no other reaction changes the mass.
___ Cu2O(s) + ___ O2(g) → ___ CuO(s)
Question 1
Give the smallest whole-number coefficients that balance the equation in the order shown. Explain how the oxygen atoms balance.
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Question 2
How does the oxidation number of copper change as Cu₂O becomes CuO?
- It decreases from +2 to +1.
- It increases from +1 to +2.
- It stays at +1.
- It changes from 0 to +2.
The class models an initial 7.15 g sample of Cu2O. If all of it changed to CuO, the product would have a mass of 7.95 g. A second model run starting with the same mass gives 7.55 g of solid.
Question 3
Calculate the mass of oxygen that entered the solid in the second run. Show how the sample masses support the answer.
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Question 4
Under the model, what fraction of the starting Cu₂O reacted in the second run? Use the complete-conversion mass for comparison.
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