Easy Notes — Grade 11 ChemistryOrganic Chemistry: Hydrocarbons and Alcohol (Chapter 8)

 

Grade 11 Chemistry

Easy Notes — Organic Chemistry: Hydrocarbons and Alcohol (Chapter 8)

Based on the Grade 11 Chemistry textbook sections on organic chemistry.

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1. Organic Chemistry

Organic chemistry is the study of carbon compounds and their reactions.

Examples:

• Methane ($CH_4$)
• Ethanol ($C_2H_5OH$)
• Benzene ($C_6H_6$)

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2. Hydrocarbons

Definition

Hydrocarbons are compounds containing only:

• Carbon (C)
• Hydrogen (H)

General form:

$$C_x{H}_{\mathrm{y}}$$

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Types of Hydrocarbons

(A) Saturated Hydrocarbons — Alkanes

• Have only single bonds
• General formula:

$C_nH_{2n+2}$

Examples:

Name	Formula
Methane	$CH_4$
Ethane	$C_2H_6$
Propane	$C_3H_8$
Butane	$C_4H_{10}$

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(B) Unsaturated Hydrocarbons

Contain double or triple bonds.

Alkenes

• Contain at least one double bond

Formula:

$C_nH_{2n}$

Examples:

Name	Formula
Ethene	$C_2H_4$
Propene	$C_3H_6$

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Alkynes

• Contain at least one triple bond

Formula:

$C_nH_{2n-2}$

Examples:

Name	Formula
Ethyne	$C_2H_2$
Propyne	$C_3H_4$

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Properties of Hydrocarbons

• Mostly insoluble in water
• Burn in air
• Usually less dense than water
• Used as fuels

Examples:

• LPG
• Petrol
• Natural gas

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Reactions of Hydrocarbons

Combustion Reaction

Hydrocarbon + Oxygen → Carbon dioxide + Water

Example:

$$CH_4 + 2O_2 \rightarrow CO_2 + 2H_2O$$

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Addition Reaction

Unsaturated hydrocarbons add atoms across multiple bonds.

Example:

$$C_2{H}_4+H_2\to C_2{H}_{\mathrm{6}}$$

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3. Alcohol

Definition

Alcohols are organic compounds containing:

$$-OH$$

called the hydroxyl group.

General formula:

$C_nH_{2n+1}OH$

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Examples of Alcohols

Name	Formula
Methanol	$CH_3OH$
Ethanol	$C_2H_5OH$
Propanol	$C_3H_7OH$

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Properties of Alcohols

• Colorless liquids
• Dissolve in water (small alcohols)
• Flammable
• Have characteristic smell

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Uses of Alcohol

Ethanol

• Medicines
• Perfumes
• Fuel
• Beverages

Methanol

• Solvent
• Fuel
• Chemical production

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Preparation of Ethanol

Ethanol can be prepared by fermentation:

$$C_6{H}_{12}{O}_6\to 2C_2{H}_{5}OH+2C{O}_{\mathrm{2}}$$

(glucose → ethanol + carbon dioxide)

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Short Tricks to Remember

Compound	Memory Trick
Alkane	Single bond
Alkene	Double bond
Alkyne	Triple bond
Alcohol	Has –OH group
Ethanol	Drinking alcohol
Methanol	Toxic alcohol

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Important Exam Questions

1. What are hydrocarbons?
2. Differentiate alkanes, alkenes and alkynes.
3. Write the general formula of alkane.
4. What is alcohol?
5. State two uses of ethanol.
6. Write the equation for fermentation.
7. Explain combustion of hydrocarbons.

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Very Short Summary

• Hydrocarbons contain only carbon and hydrogen.
• Alkanes → single bonds.
• Alkenes → double bonds.
• Alkynes → triple bonds.
• Alcohols contain the –OH group.
• Ethanol and methanol are important alcohols.