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The following equipment was set up to measure the heat of combustion of an alkanol - HSC - SSCE Chemistry - Question 9 - 2017 - Paper 1
Question 9
The following equipment was set up to measure the heat of combustion of an alkanol. Thermometer Heat shield Tripod Loose fitting lid Conical flask containing wa... show full transcript
Worked Solution & Example Answer:The following equipment was set up to measure the heat of combustion of an alkanol - HSC - SSCE Chemistry - Question 9 - 2017 - Paper 1
Step 1
Which of the following equations could account for these observations?
Answer
To determine which combustion equation accounts for the black deposits and the lower measured heat of combustion, we need to consider the products formed during combustion. The formation of black deposits indicates incomplete combustion, which occurs when there is insufficient oxygen.
Looking at the options:
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Option A: C₂H₆O + 7O₂ → 4CO₂ + 6H₂O, this represents complete combustion, hence does not account for black deposits.
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Option B: C₈H₁₈ + 4O₂ → 8CO₂ + 4H₂O, also depicts complete combustion without deposits.
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Option C: 2C₂H₆O + 3O₂ → 4CO + 2H₂O, shows the formation of carbon monoxide (CO), which suggests incomplete combustion. This could lead to black deposits.
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Option D: 2C₂H₆O + 4O₂ → 2CO₂ + 2C + 6H₂O also indicates the formation of carbon (C), explicitly accounting for the deposits observed.
Considering the evidence from the black deposits and the measured heat, the best answer which accounts for both the observations is:
D. 2C₂H₆O + 4O₂ → 2CO₂ + 2C + 6H₂O