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Alkanes
This topic links saturated hydrocarbons to crude oil, combustion, environmental effects and radical mechanisms.
11
Objectives
55
Flashcards
55
Questions
90 min
Study time
AQAA LevelChemistryOrganic chemistry
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Syllabus checklist
What you need to know
11 objective pages available
Fractional distillation and cracking4 objectives
- Explain how fractional distillation separates crude oil into fractions.
- Relate fraction properties to chain length and intermolecular forces.
- Explain why cracking is used to make more useful hydrocarbons.
- Write equations for cracking reactions.
Combustion and environmental effects4 objectives
- Write equations for complete combustion of alkanes.
- Explain formation of pollutants in internal combustion engines.
- Explain how catalytic converters reduce pollutants.
- Explain how sulfur dioxide can be removed from flue gases.
Chlorination of alkanes3 objectives
- Explain initiation, propagation and termination steps in free-radical substitution.
- Write equations for methane chlorination steps.
- Explain why ultraviolet light is needed for radical formation.
Key terms
Fractional DistillationCrude Oil Fractionsfractional distillationintermolecular forcescrackinguseful hydrocarbonsCrackingThermal Crackingcomplete combustionalkaneinternal combustion enginepollutants
Exam tips
- Understanding Fractional Distillation: Explain clearly by remember that fractional distillation separates crude oil into fractions based on boiling points. The lower the boiling point, the higher the fraction in the column. Link the point to Fractional distillation and cracking, then state the evidence, calculation, mechanism, observation, or conclusion required by the question.
- Understanding Fraction Properties: Explain clearly by relate the properties of fractions from fractional distillation to their chain lengths and intermolecular forces. Link the point to Fractional distillation and cracking, then state the evidence, calculation, mechanism, observation, or conclusion required by the question.
Common mistakes
- Misunderstanding Fractional Distillation: Fractional distillation separates crude oil into fractions based on both boiling points and the strength of intermolecular forces. The formula for separation involves understanding that components with lower boiling points and weaker intermolecular forces vaporize first. For example, lighter fractions like gasoline have lower boiling points than heavier fractions like diesel. Therefore, as the crude oil is heated, the lighter fractions rise and condense at different levels in the fractionating column.
- Misunderstanding Fraction Properties: To clarify, remember that as chain length increases, the boiling point generally increases due to stronger van der Waals forces. For example, consider the formula for boiling point trends: longer chains lead to increased surface area, which enhances intermolecular forces. Thus, longer alkanes have higher boiling points. Always relate this to the strength of intermolecular forces.
Practice preview
- Which property of the components in crude oil is primarily responsible for the separation of fractions during fractional distillation?
- During fractional distillation, at what stage is the lightest fraction, such as gasoline, collected?
- Which of the following best explains why fractional distillation can separate crude oil into distinct fractions?
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