Applications of Organic Chemistry (Grade 12 NSC Matric Physical Sciences): Revision Notes

Applications of Organic Chemistry

Organic chemistry has numerous practical applications in our daily lives and industrial processes. This section explores two major applications: the use of alkanes as fossil fuels and the production and uses of esters.

Alkanes as fossil fuels

Hydrocarbon cracking

This industrial process is essential for converting large, bulky alkane molecules into smaller, more useful compounds. The process produces shorter alkanes and alkenes that have greater commercial value and practical applications.

There are two main types of hydrocarbon cracking:

• Thermal cracking - occurs at high pressures and temperatures without using a catalyst
• Catalytic cracking - occurs at lower pressures and temperatures but uses a catalyst to speed up the reaction

The products of catalytic cracking are particularly valuable because they include both useful alkanes and unsaturated alkenes that can be used in various industrial processes.

Fractional distillation

Once crude oil has been processed through cracking, the various hydrocarbon products can be separated using fractional distillation. This separation technique works because different hydrocarbons have different boiling points.

The fractional distillation process works as follows:

• Crude oil is heated to approximately 700°C in a furnace
• The hot vapours rise through a fractionating column containing multiple trays
• Each tray is maintained at a specific temperature
• As the vapours cool while rising, compounds with higher boiling points condense first
• Lighter compounds with lower boiling points continue rising and condense at higher levels

The result is a systematic separation of hydrocarbons based on their molecular size:

• Smaller molecules (1-4 carbon atoms) are collected at the top as gases and liquid petroleum gas
• Medium-sized molecules are collected as petrol, diesel, and paraffin
• Larger molecules are collected lower down as heavier oils and waxes

Combustion of alkanes

Alkanes serve as our most important fossil fuels because their combustion reactions are highly exothermic, meaning they release large amounts of energy. This makes them ideal for heating, electricity generation, and powering vehicles.

The general equation for complete combustion of any alkane is:

$\text{alkane} + \text{O}_2\text{(g)} \rightarrow \text{CO}_2\text{(g)} + \text{H}_2\text{O(g)} + \text{energy}$

Specific examples of complete combustion include:

• Methane: $\text{CH}_4\text{(g)} + 2\text{O}_2\text{(g)} \rightarrow \text{CO}_2\text{(g)} + 2\text{H}_2\text{O(g)} + \text{energy}$
• Propane: $\text{C}_3\text{H}_8\text{(g)} + 5\text{O}_2\text{(g)} \rightarrow 3\text{CO}_2\text{(g)} + 4\text{H}_2\text{O(g)} + \text{energy}$
• Hexane: $2\text{C}_6\text{H}_{14}\text{(ℓ)} + 19\text{O}_2\text{(g)} \rightarrow 12\text{CO}_2\text{(g)} + 14\text{H}_2\text{O(g)} + \text{energy}$
• Octane: $2\text{C}_8\text{H}_{18}\text{(ℓ)} + 25\text{O}_2\text{(g)} \rightarrow 16\text{CO}_2\text{(g)} + 18\text{H}_2\text{O(g)} + \text{energy}$

Balancing combustion equations

When balancing combustion equations, follow this systematic approach:

Step 1: Balance carbon atoms first
Step 2: Balance hydrogen atoms second
Step 3: Balance oxygen atoms last
Step 4: Ensure all coefficients are whole numbers

Esters

Esters are organic compounds formed through the reaction between alcohols and carboxylic acids. They are important in both industry and biology due to their distinctive properties and pleasant fragrances.

Production of esters

The general equation for esterification is:

$\text{alcohol} + \text{carboxylic acid} \rightarrow \text{ester} + \text{water}$

More specifically:

$\text{R}'\text{-OH} + \text{R-COOH} \rightarrow \text{R}'\text{-O-CO-R} + \text{H}_2\text{O}$

Where R and R' represent different alkyl or aryl groups.

A specific example shows the reaction between butanol and propanoic acid:

$\text{CH}_3\text{CH}_2\text{CH}_2\text{CH}_2\text{OH} + \text{CH}_3\text{CH}_2\text{COOH} \rightarrow \text{CH}_3\text{CH}_2\text{COOCH}_2\text{CH}_2\text{CH}_2\text{CH}_3 + \text{H}_2\text{O}$

This produces butyl propanoate and water as products.

Naming esters

Ester names follow a specific pattern that reflects their formation from alcohols and carboxylic acids:

• The first part of the name comes from the alcohol and ends in -yl
• The second part of the name comes from the carboxylic acid and ends in -oate

Properties and uses of esters

Esters have several distinctive properties that make them valuable in various applications:

• Distinctive fragrances - many esters have pleasant, fruity smells
• Lower water solubility compared to their parent alcohols and acids
• Volatile nature - many esters evaporate easily at room temperature

Common applications of esters include:

• Flavourings - artificial fruit flavours in food products
• Fragrances - perfumes and cosmetic products
• Solvents - nail polish remover, paint thinners
• Plasticisers - making plastics more flexible
• Pharmaceuticals - active ingredients in medicines

Laboratory preparation of esters

The key steps in ester preparation are:

• Mix the alcohol and carboxylic acid in appropriate proportions
• Add a few drops of concentrated sulfuric acid as catalyst
• Heat the mixture gently in a water bath
• Cool the products and identify the ester by its distinctive odour