Chapter 11 – Organic Chemistry: Molecules, Fuels, and Ethanoic Acid Insights

Chapter 11 – Organic Chemistry unfolds the intricate world of molecular structures, functional groups, and reactions. This comprehensive guide delves into the displayed formulas of molecules, general formulae of compounds in homologous series, and the significance of functional groups in determining chemical properties. It explores homologous series, saturated and unsaturated compounds, naming conventions, and provides insights into the world of fuels, including fossil fuels, fractional distillation of petroleum, and properties and uses of various fractions. 

The chapter also unravels the characteristics of alkanes, alkenes, and alcohols, shedding light on their bonding, properties, and manufacturing processes. Discover the diverse reactions of ethanoic acid, its uses, and its interactions with metals, bases, and carbonates.

Displayed Formula Of A Molecule:

The displayed formula shows all the atoms and all the bonds in a molecule. Each atom is represented by its chemical symbol, and bonds are depicted as lines. For example, the displayed formula for ethane (C2H6)

General Formulae Of Compounds In Homologous Series:

• Alkanes (Saturated Hydrocarbons): CnH2n+2 

• Interpretation: Each member in the alkane series has a general formula
• CnH2n+2 indicates that it contains only single carbon-carbon bonds.

• Alkenes (Unsaturated Hydrocarbons): CnH2n
  • Interpretation: Each member in the alkene series has a general formula
  • CnH2n indicates the presence of at least one carbon-carbon double bond.
• Alcohols: CnH2n+1OH
  • Interpretation: Each member in the alcohol series has a general formula
  • CnH2n+1OH indicates the presence of a hydroxyl (-OH) functional group.
• Carboxylic Acids: CnH2n+1COOH
  • Interpretation: Each member in the carboxylic acid series has a general formula
  • CnH2n+1COOH indicates the presence of a carboxyl (-COOH) functional group.

Functional Group:

• Definition: A functional group is an atom or group of atoms that determines the chemical properties of a homologous series.
• Example: In alcohols, the hydroxyl (-OH) group is the functional group. The presence of this group imparts specific chemical properties to alcohols.

In summary, displayed formulas show all atoms and bonds in a molecule, general formulae represent compounds in a homologous series, and functional groups are crucial in determining the chemical properties of these series.

Homologous Series:

• Definition: A homologous series is a family of similar compounds with similar chemical properties due to the presence of the same functional group.

Saturated and Unsaturated Compounds:

• Saturated Compound: A saturated compound has molecules in which all carbon–carbon bonds are single bonds.
• Unsaturated Compound: An unsaturated compound has molecules in which one or more carbon–carbon bonds are not single bonds.

In summary, a homologous series consists of similar compounds sharing the same functional group, while saturated compounds have only single carbon–carbon bonds, and unsaturated compounds have at least one carbon–carbon bond that is not a single bond.

Naming Organic Compounds:

Type of Compound Based on Names or Formulas:

• -ane: Indicates an alkane (saturated hydrocarbon).
• -ene: Indicates an alkene (unsaturated hydrocarbon with at least one carbon–carbon double bond).
• -ol: Indicates an alcohol (compound with a hydroxyl group, -OH).

• -oic acid: Indicates a carboxylic acid (compound with a carboxyl group, -COOH).
• Molecular Formula Ending in -ane: Represents a saturated hydrocarbon.
• Molecular Formula Ending in -ene: Represents an unsaturated hydrocarbon.
• Molecular Formula Ending in -ol: Represents an alcohol.
• Molecular Formula Ending in -oic acid: Represents a carboxylic acid.

In summary, the displayed formulae and names provided cover methane, ethane, ethene, ethanol, and ethanoic acid. The compound type can be identified based on chemical names ending in -ane, -ene, -ol, or -oic acid, as well as from molecular or displayed formulas.

Fuels

• Fossil Fuels:

Coal, Natural Gas, and Petroleum.

• Methane in Natural Gas:

Methane is the main constituent of natural gas.

• Hydrocarbons:

Hydrocarbons are compounds that contain hydrogen and carbon only.

• Petroleum Composition:

Petroleum is a mixture of hydrocarbons.

Fractional Distillation of Petroleum:

• Process: Petroleum is separated into useful fractions by fractional distillation, a process based on differences in boiling points.

Properties of Fractions in Fractionating Column:

• Decreasing Chain Length: As you move up the column, fractions have decreasing carbon chain lengths.
• Higher Volatility: Fractions higher in the column are more volatile.
• Lower Boiling Points: Boiling points decrease from bottom to top.
• Lower Viscosity: Fractions at the top have lower viscosity.

Uses of Fractions:

• Refinery Gas Fraction: Used in heating and cooking.
• Gasoline/Petrol Fraction: Used as fuel for cars.
• Naphtha Fraction: Used as a chemical feedstock.
• Kerosene/Paraffin Fraction: Used as jet fuel.
• Diesel Oil/Gas Oil Fraction: Used as fuel for diesel engines.
• Fuel Oil Fraction: Used in ships and home heating systems.
• Lubricating Oil Fraction: Used for lubricants, waxes, and polishes.
• Bitumen Fraction: Used for making roads. 

In summary, fossil fuels include coal, natural gas, and petroleum. Methane is the primary constituent of natural gas. Hydrocarbons consist of hydrogen and carbon only. Petroleum is a mixture of hydrocarbons, separated into fractions by fractional distillation. The properties of fractions change in terms of chain length, volatility, boiling points, and viscosity. These fractions have various uses, including heating, cooking, fuel for cars, jet fuel, chemical feedstock, lubricants, and road construction.

Alkanes

• Bonding in Alkanes:

The bonding in alkanes is single covalent, meaning that each carbon-carbon bond within the molecule involves the sharing of a single pair of electrons.

• Properties of Alkanes:
  • Saturated Hydrocarbons: Alkanes are saturated hydrocarbons, meaning that they contain only single carbon-carbon bonds, and each carbon atom is bonded to the maximum number of hydrogen atoms.
  • General Reactivity: Alkanes are generally unreactive under normal conditions. However, they exhibit specific reactions:
  • Combustion: Alkanes readily undergo combustion reactions in the presence of oxygen to produce carbon dioxide and water.
  • Substitution by Chlorine: Alkanes can undergo substitution reactions with chlorine, where hydrogen atoms are replaced by chlorine atoms. This is a characteristic reaction of alkanes under ultraviolet (UV) light.

In summary, alkanes have single covalent bonds and are classified as saturated hydrocarbons due to the absence of multiple bonds between carbon atoms. While generally unreactive, they can undergo combustion and substitution reactions, particularly with chlorine.

Alkenes 

• Bonding in Alkenes:

The bonding in alkenes includes a double carbon–carbon covalent bond. Alkenes are unsaturated hydrocarbons due to the presence of this double bond, which allows for additional reactions and greater chemical reactivity compared to alkanes.

• Manufacture of Alkenes and Hydrogen by Cracking:
  • Process: Alkenes and hydrogen are produced by the cracking of large alkane molecules using high temperature and a catalyst.
• Reasons for Cracking of Larger Alkane Molecules:
  • Increased Demand for Shorter Hydrocarbons: Cracking is done to obtain shorter-chain hydrocarbons, such as alkenes, which are more valuable and versatile in various industrial processes.
  • Balance in Hydrocarbon Supply: Cracking helps maintain a balance in the supply of different hydrocarbons to meet specific industrial needs.

Test to Distinguish Saturated and Unsaturated Hydrocarbons:

• Bromine Water Test: 

Saturated hydrocarbons (alkanes) do not react with bromine water, while unsaturated hydrocarbons (alkenes) decolorize bromine water.

• Observation: In the presence of an alkene, bromine water changes from orange to colourless due to the addition reaction with the double bond.

In summary, alkenes have a double carbon–carbon covalent bond, making them unsaturated hydrocarbons. They are manufactured by the cracking of larger alkane molecules, driven by the demand for shorter-chain hydrocarbons. The bromine water test is a method to distinguish between saturated and unsaturated hydrocarbons, with alkenes causing decolorization of bromine water.

Alcohol 

• Manufacture of Ethanol:
  • Fermentation of Aqueous Glucose: Ethanol is produced by fermenting aqueous glucose at temperatures between 25–35 °C in the presence of yeast and in the absence of oxygen. This process converts sugars into ethanol and carbon dioxide.
  • Catalytic Addition of Steam to Ethene: Ethanol can also be manufactured by the catalytic addition of steam to ethene at high temperature (300°C) and pressure (6000 kPa/60 atm) in the presence of an acid catalyst.
• Combustion of Ethanol:

Ethanol undergoes combustion in the presence of oxygen to produce carbon dioxide and water. The balanced chemical equation for the combustion of ethanol is:

C₂H₅OH + 3O₂ → 2 CO₂+3 H₂O

This reaction releases energy and is used as a fuel.

• Uses of Ethanol:
  • As a Solvent: Ethanol serves as a solvent for various substances, making it valuable in the pharmaceutical, cosmetic, and manufacturing industries.
  • As a Fuel: Ethanol is used as a biofuel in the form of ethanol-blended gasoline. It is also used as a renewable energy source.

In summary, ethanol can be manufactured through fermentation of glucose or by catalytically adding steam to ethene. The combustion of ethanol produces carbon dioxide and water, releasing energy. Ethanol finds uses as a solvent in various industries and as a biofuel for transportation.

Reaction of Ethanoic Acid with Metals:

• Observation: Ethanoic acid does not react with metals as vigorously as strong mineral acids do. It generally undergoes a slow reaction.
• Example: Reacting ethanoic acid with zinc produces zinc ethanoate and hydrogen gas.
• Chemical Equation: ₂CH₃COOH + Zn → (CH₃COO)2Zn + H₂
• Name of Salt: Zinc ethanoate

Reaction of Ethanoic Acid with Bases:

• Observation: Ethanoic acid reacts with bases (alkalis) to form salts and water.
• Example: Reacting ethanoic acid with sodium hydroxide produces sodium ethanoate and water.
• Chemical Equation: CH₃COOH + NaOH → CH₃COONa + H₂O
• Name of Salt: Sodium ethanoate

Reaction of Ethanoic Acid with Carbonates:

• Observation: Ethanoic acid reacts with carbonates to produce salts, carbon dioxide, and water.
• Example: Reacting ethanoic acid with sodium carbonate produces sodium ethanoate, carbon dioxide, and water.
• Chemical Equation: 2CH₃COOH + Na₂CO₃→ 2CH₃COONa + CO₂ + H₂O
• Name of Salt: Sodium ethanoate

In summary, ethanoic acid reacts with metals, bases, and carbonates to form salts. Examples include zinc ethanoate with metals, sodium ethanoate with bases, and sodium ethanoate with carbonates.

Organic Chemistry – Basic Introduction

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Summary

In this exploration of Chapter 11 – Organic Chemistry, the guide navigates through the essentials of molecular representation, homologous series, and functional groups. Discern the characteristics of saturated and unsaturated compounds, understand the nomenclature based on chemical formulas, and grasp the intricacies of various fuel sources. Dive into the properties and applications of alkanes, alkenes, and alcohols, unravelling the world of organic compounds.

The chapter concludes with a detailed examination of ethanoic acid, elucidating its reactions with metals, bases, and carbonates. This comprehensive guide equips you with essential knowledge, preparing you to master the complexities of organic chemistry for your exams.