The electrolysis of aluminium oxide, Al₂O₃, makes aluminium, Al, and oxygen, O₂ - OCR Gateway - GCSE Chemistry: Combined Science - Question 5 - 2020 - Paper 1

To determine which statement about the electrolysis of aluminium oxide is correct, we need to analyze the reaction:

$2Al₂O₃ \rightarrow 4Al + 3O₂$

1. Statement A: The masses of aluminium and oxygen formed are the same.

   • This statement is incorrect because aluminum (Al) is produced in a different quantity than oxygen (O₂). From the equation, we see that for every 2 moles of Al₂O₃, 4 moles of Al and 3 moles of O₂ are produced.

2. Statement B: The mass of aluminium decreases.

   • This statement is incorrect as well because aluminium is being produced during the electrolysis process, so its mass increases, not decreases.

3. Statement C: The mass of aluminium oxide increases.

   • This statement is also incorrect. During electrolysis, aluminium oxide is being broken down to produce aluminium and oxygen; therefore, its mass decreases.

4. Statement D: The mass of oxygen increases.

   • This statement is correct. The total mass of the components has to be conserved according to the law of conservation of mass. While the mass of aluminium oxide decreases, the mass of the produced oxygen reflects the decrease and thus increases the overall mass of the gaseous products.

Therefore, the correct answer is D: The mass of oxygen increases.