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Chemistry - Introduction to Organic Chemistry (Hydrocarbons and Functional Groups)

Grade 10IB

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

Organic chemistry is the study of carbon-based compounds. Carbon is unique because it can form four covalent bonds, allowing for the formation of long chains and rings (catenation).

Hydrocarbons are compounds consisting entirely of hydrogen and carbon atoms. They are classified into saturated (CCC-C single bonds) and unsaturated (containing C=CC=C double or CCC \equiv C triple bonds).

A Homologous Series is a family of organic compounds with the same general formula, similar chemical properties, and a graduation in physical properties (like boiling point) as the chain length increases.

Alkanes are saturated hydrocarbons with the general formula CnH2n+2C_nH_{2n+2}. They are relatively unreactive except for combustion and substitution reactions with halogens under UVUV light.

Alkenes are unsaturated hydrocarbons containing at least one C=CC=C double bond, with the general formula CnH2nC_nH_{2n}. They are more reactive than alkanes and undergo addition reactions.

Functional Groups are specific atoms or groups of atoms within molecules that determine the chemical reactivity of the molecule. Examples include the hydroxyl group (OH-OH) in alcohols and the carboxyl group (COOH-COOH) in carboxylic acids.

Isomers are molecules that have the same molecular formula but different structural arrangements (e.g., but1enebut-1-ene and but2enebut-2-ene).

📐Formulae

CnH2n+2 (General formula for Alkanes)C_nH_{2n+2} \text{ (General formula for Alkanes)}

CnH2n (General formula for Alkenes)C_nH_{2n} \text{ (General formula for Alkenes)}

CnH2n2 (General formula for Alkynes)C_nH_{2n-2} \text{ (General formula for Alkynes)}

CnH2n+1OH (General formula for Alcohols)C_nH_{2n+1}OH \text{ (General formula for Alcohols)}

CnH2n+1COOH (General formula for Carboxylic Acids, where n0)C_nH_{2n+1}COOH \text{ (General formula for Carboxylic Acids, where } n \ge 0)

💡Examples

Problem 1:

Identify the name and molecular formula of an alkane containing 55 carbon atoms.

Solution:

Pentane, C5H12C_5H_{12}

Explanation:

Using the general formula CnH2n+2C_nH_{2n+2} where n=5n=5, we calculate H=(2×5)+2=12H = (2 \times 5) + 2 = 12. The prefix for 5 carbons is 'pent-', and the suffix for alkanes is '-ane'.

Problem 2:

Describe the chemical test to distinguish between C2H6C_2H_6 and C2H4C_2H_4.

Solution:

Add bromine water (Br2(aq)Br_2(aq)) to both substances.

Explanation:

Ethane (C2H6C_2H_6) is an alkane and will not react with bromine water (it remains orange/brown). Ethene (C2H4C_2H_4) is an alkene; it undergoes an addition reaction, decolorizing the bromine water from orange to colorless.

Problem 3:

Draw and name the structural isomer of C4H10C_4H_{10} that is not a straight chain.

Solution:

2-methylpropane, CH3CH(CH3)CH3CH_3CH(CH_3)CH_3

Explanation:

While butane is a straight chain of 4 carbons, 2-methylpropane (also called isobutane) consists of a 3-carbon main chain with a methyl group (CH3-CH_3) attached to the second carbon.