Alcohols and Carboxylic Acids - GCSE Chemistry
Introduction
- Chemistry is the study of substances and their reactions.
- In this blog, we are studying organic chemistry, which focuses on carbon-based compounds.
- Two important types are alcohols and carboxylic acids, found in many everyday products.
- Alcohols are used in fuels, medicines, and sanitizers, while acids are used in food preservation, cosmetics, and manufacturing.
- Understanding them helps explain their reactions, uses, and role in daily life.
What are Organic Compounds?
- Organic compounds are chemical substances mainly made of carbon and hydrogen.
- These compounds often combine with elements such as oxygen, nitrogen, or sulphur.
- They form the basis of life and are found all around us; common examples include alcohols, carboxylic acids, hydrocarbons, and esters.
- Understanding them helps in creating new materials and improving everyday products.
- These compounds are widely used in fuels, medicines, plastics, cosmetics, food, fabrics, cleaning agents, and perfumes.
What is a Homologous Series?
- A homologous series is a group of organic compounds that have the same functional group and similar chemical properties.
- Their physical properties change gradually, including boiling point and solubility.
- Each member of a homologous series differs by a –CH₂– unit, which helps predict their reactions and properties easily.
- Such series are:
Alcohol Series:
- methanol, ethanol, propanol, butanol.
Carboxylic Acid Series:
- methanoic acid, ethanoic acid, propanoic acid, butanoic acid.
What are Alcohols?
- Alcohols are organic compounds that contain a hydroxyl (–OH) group attached to a carbon atom.
- Alcohols are classified based on which carbon atom the –OH group is attached to:
Primary Alcohols:
- The –OH group is attached to a carbon bonded to one other carbon.
Secondary Alcohols:
- The –OH group is attached to a carbon bonded to two other carbons.
Tertiary Alcohols:
- The –OH group is attached to a carbon bonded to three other carbons.
Properties:
- They are soluble in water.
- They burn to release energy, making them useful as fuels.
- They can react with acids to form esters or with metals to produce hydrogen.
- They are used as solvents, antiseptics, and in industrial chemical production.
- Some alcohols are also used in cosmetics, perfumes, and medicines.
How to Represent Alcohols?
- Alcohols can be represented using two main types of formula:
Molecular Formula:
- Indicates the total number of each type of atom in a molecule. For Example:
Structural Formula:
- Shows how the atoms are arranged and bonded, highlighting the –OH group clearly. For Example:
Note: Structural formulae show how atoms in alcohols are arranged. They help predict reactions, boiling points, solubility, and chemical behavior.
How do Alcohols Burn?
- Alcohols burn in oxygen to produce carbon dioxide, water, and energy, making the reaction highly exothermic.
- This reaction is called the combustion of alcohol.
For Example: When ethanol burns, according to the equation:
- This property makes alcohols useful as energy sources and allows the study of energy changes in chemical reactions.
Key Points:
- Longer alcohol chains release more energy per mole because they have more carbon and hydrogen atoms.
- Alcohols are used as fuels in laboratory burners, camping stoves, and as biofuels.
- Measuring the temperature change in water during combustion helps compare the energy released by different alcohols.
What are Carboxylic Acids?
- Carboxylic acids are organic compounds that have a –COOH group, which makes them acidic.
- They are weak acids because they do not completely ionize in water.
- These acids are essential in food preservation, cleaning agents, and chemical synthesis.
Reactions of Carboxylic Acids:
- Reaction with metals: Produces a salt and hydrogen gas. For Example:
- Reaction with alcohols: Forms esters and water. For Example:
- Reaction with bases: Neutralizes to form a salt and water. For Example:
How to Represent Carboxylic Acids?
- Carboxylic acids can also be represented in two ways:
Molecular Formula:
- Shows the total number of atoms. For Example:
Structural Formula:
- Shows how the atoms are arranged and bonded, highlighting the –OH group clearly. For Example:
Note: Structural formulae of carboxylic acids show how the –COOH group is attached to the carbon chain. They help explain acidity, reactions with metals and bases, and the formation of esters.
How do Alcohols Oxidize to Acids?
- Primary alcohols can be oxidized to form carboxylic acids.
- This happens when oxygen is added, either from the air (slowly) or using an oxidizing agent such as acidified potassium dichromate (K₂Cr₂O₇).
- During oxidation, the alcohol first forms an aldehyde, which is then further oxidized to an acid.
Examples:
- Oxidation of Ethanol: When ethanol (C₂H₅OH) is oxidized, it first forms ethanal (CH₃CHO) and then ethanoic acid (CH₃COOH).
- Oxidation of Propanol: When propanol (C₃H₇OH) is oxidized, it forms propanoic acid (C₂H₅COOH) and water.
- Oxidation of Butanol: When butanol (C₄H₉OH) is oxidized, it forms butanoic acid (C₃H₇COOH) and water.
Key Points:
- Primary alcohols can be oxidized to form carboxylic acids, while secondary alcohols can be oxidized to form ketones.
- Tertiary alcohols do not oxidize easily.
- This oxidation is important in producing useful acids like ethanoic acid for industrial and laboratory use.
Frequently Asked Questions
Solution:
Organic compounds are substances made mainly of carbon and hydrogen, often with oxygen or nitrogen.
- They form the basis of life and are found in fuels, plastics, medicines, and food.
- Carbon’s ability to form long chains and rings makes millions of organic compounds possible.
Solution:
Alcohols are a group of organic compounds that contain the hydroxyl (–OH) functional group. They follow the general formula CₙH₂ₙ₊₁OH.
Examples include:
- Methanol (CH₃OH) – used as a solvent and fuel.
Solution:
When alcohols burn in oxygen, they undergo complete combustion to produce carbon dioxide and water. This reaction releases energy, so it is exothermic. Example (for ethanol):
C₂H₅OH + 3O₂ → 2CO₂ + 3H₂O + energy
Solution:
Ethanol is made by fermenting sugar with yeast in anaerobic conditions. Yeast converts glucose into ethanol and carbon dioxide.
C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂
Solution:
Fermentation makes dilute ethanol (about 15%). It is heated and distilled, and because ethanol boils at 78°C, it evaporates first, then condenses to give pure ethanol.
Solution:
Carboxylic acids react with metals to form hydrogen gas and a salt, and with carbonates to produce carbon dioxide.
Examples:
- 2CH₃COOH + Mg → (CH₃COO)₂Mg + H₂
- 2CH₃COOH + Na₂CO₃ → 2CH₃COONa + H₂O + CO₂