Quick Notes

Quick Notes

Chemistry Chapter 2: Carbon Compound
2.1 Types of Carbon Compounds
Types of Carbon Compounds
CHEMISTRY • Form 5 • Chapter 2: Carbon Compounds

2.1Types of Carbon Compounds

Carbon compounds are broadly classified into organic and inorganic compounds. Organic compounds are further divided into hydrocarbons and non-hydrocarbons. Hydrocarbons are essential energy sources mainly obtained from the refining of petroleum via fractional distillation and cracking. As petroleum reserves deplete, alternative renewable sources from biomass are being developed.

Learning Objectives

  • Understand carbon compounds, including the difference between organic and inorganic carbon compounds.
  • Classify hydrocarbons into saturated and unsaturated hydrocarbons based on their covalent bonds.
  • Explain the sources of hydrocarbons, particularly petroleum refining through fractional distillation and cracking.
  • Describe laboratory fractional distillation of petroleum and relate fraction properties to boiling points.
  • Identify renewable alternative sources of hydrocarbons derived from biomass.

Petroleum Fractionating Tower and Product Profiles

How petroleum fractions separate according to boiling points, molecular size, and physical properties, together with their daily uses.

Petroleum fractionating tower A vertical fractionating tower showing eight petroleum fractions from petroleum gas at the top to bitumen at the bottom, with temperature ranges and daily uses. Petroleum Fractionating Tower Lower boiling point at the top • Higher boiling point at the bottom Petroleum gas C₁–C₄ • < 40 °C Cooking gas Petrol C₅–C₉ • 40–75 °C Fuel for motor vehicles Naphtha C₅–C₁₀ • 75–150 °C Petrochemical raw materials Kerosene C₁₀–C₁₆ • 160–250 °C Fuel for aircraft Diesel oil C₁₄–C₂₀ • 125–300 °C Fuel for heavy vehicles Lubricating oil C₂₀–C₅₀ • 300–350 °C Lubricating oil and candles Fuel oil C₂₀–C₇₀ • 350–500 °C Fuel for ships and power stations Bitumen > C₇₀ • > 500 °C Road pavements Lower boiling point Higher boiling point

Brief Explanation

Understand the key ideas about carbon compounds and hydrocarbons.

Carbon compounds are broadly classified into organic compounds and inorganic compounds.

Organic Compounds

Compounds originating from living things that contain carbon covalently bonded with other elements. Early chemists defined them as compounds from animals or plants, such as petroleum, carbohydrate, protein, fat and urea. Today, organic compounds also include laboratory-synthesised compounds of natural ingredients, such as plastics, perfumes, detergents and medicines.

Inorganic Compounds

Compounds originating from non-living materials. Examples include oxides of carbon such as \(\text{CO}_2\), carbonate compounds such as \(\text{PbCO}_3\), and cyanide compounds.

Hydrocarbons

Organic compounds containing only hydrogen and carbon. Examples include petrol and natural gas.

Non-Hydrocarbons

Organic compounds containing carbon, hydrogen, and other elements such as oxygen, nitrogen, phosphorus, or halogens. Examples include protein, starch, fat and alcohol.

Saturated Hydrocarbons

Hydrocarbons containing only single bonds between carbon atoms. Example: propane, \(\text{C}_3\text{H}_8\).

Unsaturated Hydrocarbons

Hydrocarbons containing at least one double bond or triple bond between carbon atoms. Examples: ethene with a \(\text{C}=\text{C}\) double bond, propyne/ethyne with a \(\text{C}\equiv\text{C}\) triple bond.

Fraction Carbon range Boiling range Daily use
Petroleum gas\(\text{C}_1 - \text{C}_4\)< 40 °CCooking gas
Petrol\(\text{C}_5 - \text{C}_9\)40 °C – 75 °CFuel for motor vehicles
Naphtha\(\text{C}_5 - \text{C}_{10}\)75 °C – 150 °CRaw materials for petrochemical industry
Kerosene\(\text{C}_{10} - \text{C}_{16}\)160 °C – 250 °CFuel for aircraft
Diesel oil\(\text{C}_{14} - \text{C}_{20}\)125 °C – 300 °CFuel for heavy vehicles such as buses and lorries
Lubricating oil\(\text{C}_{20} - \text{C}_{50}\)300 °C – 350 °CLubricating oil and candles
Fuel oil\(\text{C}_{20} - \text{C}_{70}\)350 °C – 500 °CFuel for ships and power stations
Bitumen> \(\text{C}_{70}\)> 500 °CRoad pavements
Fractional distillation separates fractions because each fraction has its own boiling point. As molecule size increases, the van der Waals forces between molecules become stronger, requiring more heat energy to overcome; thus, boiling point increases. Hydrocarbons with a lower boiling point vaporise first, rise to the top of the fractionating tower, condense, and are separated. Hydrocarbons with a higher boiling point are collected at the bottom of the tower and condense into liquid.
Cracking is the process of breaking long-chain hydrocarbons into smaller hydrocarbons. It is carried out at high temperature and high pressure, using a catalyst such as a mixture of aluminium oxide (\(\text{Al}_2\text{O}_3\)) and silicon(IV) oxide (\(\text{SiO}_2\)) to increase the reaction rate. Products include smaller hydrocarbons, shorter-chain alkane and alkene hydrocarbons, and hydrogen gas (\(\text{H}_2\)).
Examples of cracking reactions:
\(\text{C}_7\text{H}_{16} \rightarrow \text{C}_2\text{H}_4 + \text{C}_5\text{H}_{12}\) (Heptane → Ethene + Pentane)
\(\text{C}_{10}\text{H}_{22} \rightarrow 2\text{C}_5\text{H}_{10} + \text{H}_2\) (Decane → Pentene + Hydrogen)
Alternative sources of hydrocarbon: Scientists predict petroleum reserves will be exhausted within 100 years. Renewable alternatives derived from biomass include bioethanol, biodiesel and biogas. Biomass is organic matter of plants and animals containing latent energy derived from the sun.

Try These Questions First

Answer mentally, then check the explanation.

1

State two differences between saturated and unsaturated hydrocarbons.

Answer: (1) Saturated hydrocarbons contain only single covalent bonds between carbon atoms, whereas unsaturated hydrocarbons contain at least one double or triple bond. (2) Saturated hydrocarbons include alkanes, whereas unsaturated hydrocarbons include alkenes and alkynes.
2

Why are porcelain chips added into the round bottom flask during the fractional distillation of petroleum?

Answer: Porcelain chips are added to ensure smooth boiling and prevent bumping of the petroleum liquid.
3

State the catalyst used in the industrial cracking of long-chain hydrocarbons.

Answer: A mixture of aluminium oxide (\(\text{Al}_2\text{O}_3\)) and silicon(IV) oxide (\(\text{SiO}_2\)).

Common Mistakes

Avoid these errors when classifying carbon compounds and explaining petroleum refining.

!
Confusing "organic compounds" with "hydrocarbons" by assuming all organic compounds contain only carbon and hydrogen. Many contain oxygen, nitrogen, sulphur, or phosphorus, making them non-hydrocarbons like alcohols and proteins.
!
Classifying all carbon-containing compounds as organic, forgetting that \(\text{CO}_2\), carbonates (\(\text{CO}_3^{2-}\)), and cyanides (\(\text{CN}^-\)) are inorganic compounds.
!
Assuming that cracking and fractional distillation are the same process. Fractional distillation is a physical separation based on boiling points, while cracking is a chemical breakdown using heat and catalysts.

Common Misconceptions

Compare each misconception with the correct fact.

Misconception

Saturated hydrocarbons burn with more soot than unsaturated hydrocarbons.

Correct Fact

Unsaturated hydrocarbons (such as alkenes) generally have a higher percentage of carbon by mass compared to saturated hydrocarbons of similar chain length, producing more soot upon combustion.

Misconception

Crude petroleum can be directly used as car fuel without processing.

Correct Fact

Petroleum is a complex mixture of simple and long-chain hydrocarbons that cannot be used directly; it must be separated into fractions and cracked before use.

Summary

Key facts to remember.

  • Carbon Compounds: Divided into Organic (covalently bonded carbon originating from living things or synthetic laboratory equivalents) and Inorganic (\(\text{CO}_2\), carbonates, cyanides).
  • Hydrocarbons vs Non-Hydrocarbons: Hydrocarbons contain only \(\text{C}\) and \(\text{H}\). Non-hydrocarbons also contain \(\text{O}\), \(\text{N}\), \(\text{S}\), \(\text{P}\), or halogens.
  • Saturation: Saturated = only single \(\text{C}-\text{C}\) bonds. Unsaturated = has \(\text{C}=\text{C}\) or \(\text{C}\equiv\text{C}\) bonds.
  • Petroleum Refining: Fractional distillation separates hydrocarbons by boiling points and molecular sizes. Cracking breaks long chains into smaller, high-demand molecules and alkenes using \(\text{Al}_2\text{O}_3\) and \(\text{SiO}_2\) catalysts.
  • Alternative Hydrocarbons: Renewable biomass fuels such as bioethanol, biodiesel, and biogas.

Quick Activity

Complete all parts before checking your score.

A. Objective Quiz

1

Which of the following substances is an inorganic carbon compound?

2

What is the function of aluminium oxide, \(\text{Al}_2\text{O}_3\), and silicon(IV) oxide, \(\text{SiO}_2\), in the cracking process?

B. Fill in the Blanks

3

Hydrocarbons containing only single bonds between carbon atoms are classified as ______ hydrocarbons.

4

In fractional distillation, fractions collected at the top of the tower have a ______ boiling point than fractions collected at the bottom.

C. Match the Substance with Its Use or Description

Drag each substance on desktop. On mobile, tap a substance and then tap the matching box.

Answer Choices

Petroleum gas (\(\text{C}_1 - \text{C}_4\)) Kerosene (\(\text{C}_{10} - \text{C}_{16}\)) Bitumen (> \(\text{C}_{70}\)) Bioethanol

Use or Description

1Cooking gas collected at temperatures below 40 °C
2Fraction boiling between 160 °C and 250 °C used as fuel for aircraft
3High boiling residue (> 500 °C) used for road pavements
4Renewable alternative fuel produced from biomass or food wastes
Complete every answer before checking.
 

Keywords

Tap or hover over a term to read its meaning.

Carbon compound Organic compound Inorganic compound Hydrocarbon Non-hydrocarbon Saturated hydrocarbon Unsaturated hydrocarbon Fractional distillation Cracking Biomass