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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 | ... 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 today's atmosphere has decreased primarily because the Earth cooled over time. Initially, high temperatures facilitated the presence of significant water vapour, which eventually condensed as the atmosphere cooled, forming oceans and other bodies of water.
Step 2
Calculate the percentage of oxygen in this sample of dry air.
Answer
To find the percentage of oxygen, we can use the formula:
ext{Percentage of oxygen} = rac{ ext{initial volume of air} - ext{final volume of gas}}{ ext{initial volume of air}} imes 100Substituting 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 ext{ %}Step 3
Step 4
Explain what happened to allow the change to occur.
Answer
As the Earth's environment evolved, processes such as volcanic activity released iron oxide into the atmosphere. Over time, these oxide compounds reacted with the available iron sulfide under varying conditions, leading to the incorporation of iron oxide in the rocks.