4b-Crude oil Flashcards
Q: What are alkanes?
A: Alkanes are a homologous series of saturated hydrocarbons with the general formula CₙH₂ₙ₊₂. They contain only single covalent bonds between carbon atoms.
Q: What are the first four alkanes and their molecular formulas?
A:
Methane (CH₄)
Ethane (C₂H₆)
Propane (C₃H₈)
Butane (C₄H₁₀)
Q: What are the physical properties of alkanes?
Alkanes are non-polar molecules, making them insoluble in water.
They have low boiling points, which increase with molecular size due to stronger van der Waals forces.
They are less dense than water.
They are colorless and odorless in pure form.
How do alkanes react with oxygen complete combustion
Complete Combustion (excess oxygen): Produces carbon dioxide and water.
Example: CH₄ + 2O₂ → CO₂ + 2H₂O
How do alkanes react with oxygen Incomplete combustion
Incomplete Combustion (limited oxygen): Produces carbon monoxide (CO) or carbon (soot) and water.
Example: CH₄ + O₂ → CO + 2H₂O
Why is carbon monoxide (CO) dangerous
?A: Carbon monoxide binds to hemoglobin in the blood, reducing oxygen transport, which can be fatal.
Q: Are alkanes reactive?
A: Alkanes are relatively unreactive because they have strong C–C and C–H single bonds, making them stable.
What type of reaction do alkanes undergo?
Substitution Reactions (with halogens under UV light)
Example: Methane + Chlorine → Chloromethane + Hydrogen chloride
CH₄ + Cl₂ → CH₃Cl + HCl (under UV light)
Do alkanes show isomerism?
Yes, alkanes with four or more carbon atoms can have structural isomers, where the arrangement of atoms differs but the molecular formula remains the same.
Example:
Butane (C₄H₁₀) has two isomers:
n-Butane: Straight-chain structure
2-Methylpropane: Branched-chain structure
Practical: Investigating Alkane Combustion
Testing for Complete vs. Incomplete Combustion
Method: Burn an alkane and pass the gas through limewater.
Observation:
If limewater turns cloudy, CO₂ is present (complete combustion).
If soot forms, incomplete combustion occurred.
Practical: Investigating Alkane Combustion
Testing for Alkane Reactivity
Method: Bubble an alkane through bromine water.
Observation:
No color change: Confirms the presence of an alkane (saturated compound).
Color change from orange to colorless indicates an alkene (not an alkane).
