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When two mole of an organic compound is burnt in oxygen eight mole of carbon dioxide gas is formed - VCE - SSCE Chemistry - Question 15 - 2002 - Paper 1
Question 15
When two mole of an organic compound is burnt in oxygen eight mole of carbon dioxide gas is formed. In a second test, when a few drops of bromine are added to the co... show full transcript
Worked Solution & Example Answer:When two mole of an organic compound is burnt in oxygen eight mole of carbon dioxide gas is formed - VCE - SSCE Chemistry - Question 15 - 2002 - Paper 1
Step 1
Analyze the combustion reaction
Answer
Given that two moles of the organic compound produce eight moles of carbon dioxide, we can determine the combustion reaction. In complete combustion, the reaction with oxygen can be represented as:
ightarrow CO_2 + H_2O$$ From the information provided, since 8 moles of CO₂ are produced from 2 moles of the compound, this means: $$2 C_xH_y ightarrow 8 CO_2$$ This implies that 1 mole of the compound produces 4 moles of CO₂. Hence, the stoichiometry indicates that each carbon (C) in the compound yields one CO₂.Step 2
Determine the possible formulas
Answer
Since 1 mole of the compound yields 4 moles of CO₂, we conclude the compound contains 4 carbon atoms (C₄). Therefore, the remaining part of the formula involves determining the number of hydrogen atoms.
The general formula for alkanes can be represented as:
For alkenes, it is:
Based on the provided options, we infer the molecular formula must be suitable for the reactivity with bromine, indicating it may be an alkene or alkane.
Step 3
Identify the correct option based on reactivity
Answer
The rapid decolouration of bromine indicates the presence of unsaturation (double bonds) in the molecule. Thus, the compound must be an alkene. For four carbons, the suitable alkene according to the formula would be:
- C₄H₈, which corresponds to option A: C₈H₈ since it matches the unsaturation requirement and matches the carbon count derived from the combustion data.
Step 4