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This question is about oxygen - Edexcel - GCSE Chemistry - Question 7 - 2022 - Paper 1
Question 7
This question is about oxygen. (a) The percentage of oxygen in today's atmosphere is greater than the percentage of oxygen in the Earth's early atmosphere. Explain... show full transcript
Worked Solution & Example Answer:This question is about oxygen - Edexcel - GCSE Chemistry - Question 7 - 2022 - Paper 1
Step 1
Explain what caused this change to happen.
Answer
The increase in the percentage of oxygen in the Earth's atmosphere is primarily due to photosynthesis, a process carried out by green plants and cyanobacteria. Early in Earth's history, volcanic activity released gases, including carbon dioxide and nitrogen, but very little oxygen. Over time, plants evolved and began to use sunlight to convert carbon dioxide and water into glucose and oxygen through photosynthesis. This process gradually increased the concentration of oxygen in the atmosphere, leading to the levels we observe today.
Step 2
Explain how the student could check that the magnesium had reacted completely with oxygen.
Answer
The student could check if the magnesium reacted completely with oxygen by measuring the mass of the crucible, lid, and contents before and after the reaction. If the mass remains constant after heating and cooling, this suggests that the magnesium has completely reacted with oxygen to form magnesium oxide. Any increase in mass would indicate unreacted magnesium or incomplete combustion.