Organic chemistry 1

Understanding Alkanes

Definition and Structure

Alkanes are fundamental hydrocarbons consisting of hydrogen and carbon atoms. They feature:

• ✦ Single covalent bonds between carbon atoms
• ✦ General formula: C_nH_2n+2
• ✦ Saturated hydrocarbon structure

Properties

Reactivity: Relatively unreactive due to stable carbon-carbon single bonds

Key Reactions: Combustion and halogen substitution

Example Reaction:

CH₄ + Cl₂ →_{[UV light]} CH₃Cl + HCl

Uses of Alkanes

Fuels

Primary use in natural gas, heating, and vehicle fuel

Waxes

Used in candles and protective coatings

Lubricating Oils

Essential for machinery and industrial applications

Environmental Impact of Methane

Greenhouse Gas Properties

• ► 20x more potent than CO₂ over 100 years
• ► Significant contributor to global warming

Sources

• Agricultural activities
• Wetland decomposition
• Fossil fuel extraction

Effects

• Rising global temperatures
• Melting ice caps
• Extreme weather events

Substitution Reactions

CH₄ + Cl₂ →_{[UV light]} CH₃Cl + HCl

Step 1: UV Activation

UV light provides energy to break halogen bonds

Step 2: Radical Formation

Halogen radicals form and react with alkane

Isomers of C₆H₁₄

n-Hexane

CH3-CH2-CH2-CH2-CH2-CH3
            

2-Methylpentane

    CH3
     |
CH3-CH-CH2-CH2-CH3
            

Alkenes

Key Properties

• Contains C=C double bond
• More reactive than alkanes
• General formula: C_nH_2n

Hydrogenation

Converts alkenes to alkanes using H₂ gas

Hydration

Forms alcohols by adding H₂O

Polymers and Plastics

Addition Polymerization

A process where small alkene molecules (monomers) join to form long chain molecules (polymers).

nCH₂=CH₂ → [-CH₂-CH₂-]_n

Ethene to Polyethene

Poly(ethene)

• Most common plastic
• Used in packaging
• Flexible and durable

PVC

• Used in construction
• Chemical resistant
• Durable pipes and cables

PTFE

• Non-stick properties
• Heat resistant
• Chemical inert

Environmental Challenges

Non-biodegradable Plastics

⚠ Persists in environment for hundreds of years

Landfill Impact

• Space consumption
• Soil contamination
• Long-term persistence

Ocean Pollution

• Marine life danger
• Microplastic formation
• Ecosystem damage

Safety Considerations

Carbon Monoxide Hazard

⚠ Colorless, odorless toxic gas produced when burning plastics

Prevention

• Proper disposal methods
• Avoid burning plastics
• Use recycling facilities

Safety Measures

• Ventilation requirements
• Protective equipment
• Emergency procedures

Last updated: October 24, 2024

Quiz 1:
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Quiz 2:

Chemistry Answers

Question 1

a. Ethene is classified as an unsaturated hydrocarbon because it contains a double bond between carbon atoms.

b. The cracking process of breaking down long-chain alkanes into simpler alkanes and alkenes is vital for the petrochemical industry as it produces more useful raw materials for various products.

c. Converting ethene to ethanol is an addition reaction where a water molecule (H2O) is added across ethene's double bond.

Timer: 2:00

Question 2

a. Identification of substances:

• A = Nickel (catalyst)
• B = Ethane (C2H6)
• C = Carbon dioxide (CO2)
• D = Sulfuric acid (H2SO4)
• E = Ethanol (C2H5OH)
• F = Dibromoethane (C2H4Br2)

b.

i. Reaction forming liquid E: C2H4 + H2O → C2H5OH

ii. Reaction conditions: Temperature 300°C, high pressure, sulfuric acid catalyst

c. Gas B belongs to alkanes (CnH2n+2)

d. Gas C can be identified using limewater - forms white precipitate

Timer: 2:00

Question 3

a. Term explanations:

• Hydrocarbons: Compounds containing only hydrogen and carbon atoms
• Homologous series: Series of compounds with similar structure differing by -CH2- units
• Alkanes: Saturated hydrocarbons with general formula CnH2n+2

b.

i. Methane reaction with chlorine: CH4 + Cl2 → CH3Cl + HCl

ii. Reaction type: Substitution

Timer: 2:00

Question 4

a. The type of chemical change shown is polymerization, where many ethene molecules join together to form a long chain polymer.

b. The product formed is polyethene (or polyethylene).

c.

i. Test for ethene: Bubble through bromine water - orange-brown color decolorizes

ii. Product formula: Br-CH2-CH2-Br (dibromoethane)

Timer: 2:00

Question 5

a.

i. Plastic bags should not be thrown away because:

• Take hundreds of years to decompose
• Cause pollution and harm wildlife
• Clog waterways and drainage systems

ii. Benefits of recycling plastic bags:

• Conserves natural resources
• Reduces landfill waste
• Saves energy

iii. Advantage over paper bags: Waterproof and more durable

b. Key terms:

i. Element: Pure substance that cannot be broken down further

ii. Hydrocarbon: Compound containing only carbon and hydrogen

iii. Exothermic: Reactions that give out heat energy

iv. Carbon monoxide: Toxic gas produced when burned in limited air

Timer: 2:00

Question 6

a. Categories:

Alkanes (CnH2n+2):

• C5H12 (pentane)
• C20H42 (icosane)
• C9H20 (nonane)
• C8H18 (octane)

Alkenes (CnH2n):

• C12H24
• C6H12
• C2H4 (ethene)

Neither:

• CH3 (methyl radical)
• C6H6 (benzene)
• C3H7 (propyl radical)

b. Structural isomers of C6H14:

1. n-hexane: CH3-CH2-CH2-CH2-CH2-CH3
2. 2-methylpentane: CH3-CH(CH3)-CH2-CH2-CH3
3. 3-methylpentane: CH3-CH2-CH(CH3)-CH2-CH3
4. 2,2-dimethylbutane: CH3-C(CH3)2-CH2-CH3
5. 2,3-dimethylbutane: CH3-CH(CH3)-CH(CH3)-CH3
    

Timer: 2:00

Quiz 3:
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