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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 | re... 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 decreased due to the cooling of the Earth. As the Earth's temperature lowered, the water vapour condensed to form liquid water, leading to the formation of oceans and lakes. This process effectively reduced the amount of water vapour in the atmosphere.
Step 2
Calculate the percentage of oxygen in this sample of dry air.
Answer
To calculate the percentage of oxygen in dry air, we can use the formula:
ext{Percentage of Oxygen} = rac{ ext{Initial Volume} - ext{Final Volume}}{ ext{Initial Volume}} imes 100
Substituting the given 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\%
Thus, the percentage of oxygen in the air sample is 20%.
Step 3
The apparatus and air contents must be allowed to cool because...
Answer
The apparatus and air contents must be allowed to cool before measuring the final volume of gas because heating can cause the gas to expand. If the gas remains warm, it may occupy a larger volume than it would at room temperature, leading to inaccurate measurements of the gas volume.
Step 4
Explain what happened to allow this change to occur.
Answer
The change in the Earth's earliest rocks from containing iron sulfide to containing iron oxide occurred due to the introduction of oxygen into the atmosphere. This increase in atmospheric oxygen, likely due to biological activity, facilitated the oxidation of iron sulfide to iron oxide, thereby altering the composition of the rocks.