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The Earth’s atmosphere contains several gases - Edexcel - GCSE Chemistry Combined Science - Question 1 - 2018 - Paper 1
Question 1
The Earth’s atmosphere contains several gases. Figure 1 shows the relative amounts of gases thought to be in the Earth’s early atmosphere. | gas | rela... show full transcript
Worked Solution & Example Answer:The Earth’s atmosphere contains several gases - Edexcel - GCSE Chemistry Combined Science - Question 1 - 2018 - Paper 1
Step 1
Explain why the amount of water vapour in the atmosphere has decreased.
Answer
The amount of water vapour in the atmosphere has decreased primarily due to the cooling of the Earth. As the Earth cooled, the temperature of the atmosphere decreased, leading to the condensation of water vapour. This resulted in the formation of oceans and other large bodies of water. Consequently, the concentration of water vapour in the atmosphere has diminished significantly compared to the Earth's early atmosphere.
Step 2
Calculate the percentage of oxygen in this sample of dry air.
Answer
To calculate the percentage of oxygen in the sample of dry air, we use the formula:
ext{Percentage of oxygen} = rac{ ext{Initial volume} - ext{Final volume}}{ ext{Initial volume}} imes 100Plugging in the values:
ext{Percentage of oxygen} = rac{50 ext{ cm}^3 - 40 ext{ cm}^3}{50 ext{ cm}^3} imes 100 = rac{10 ext{ cm}^3}{50 ext{ cm}^3} imes 100 = 20\%Therefore, the percentage of oxygen in the air is 20%.
Step 3
The apparatus and its contents must be allowed to cool because...
Answer
The apparatus and its contents must be allowed to cool to ensure accurate measurement of the gas volume. If the apparatus is still warm, the gas would not condense correctly, leading to an erroneous final volume that does not reflect the actual amount of gas present after all oxygen has been removed.
Step 4
Explain what happened to allow this change to occur.
Answer
The change from iron sulfide to containing iron oxide occurred due to environmental changes, particularly the increase in oxygen levels in the Earth's atmosphere. As photosynthetic organisms began to produce oxygen, this oxygen reacted with the iron sulfide present in rocks, oxidizing it to form iron oxide. This reaction indicates a significant shift in the chemical composition of early Earth and the atmosphere.