IGCSE Chemistry: Topic 4 - Organic Chemistry

Match the following empirical formulas with their corresponding alkane types.

• General formula for alkynes

• CnH2n+2

• General formula for alkanes

• CnH2n-2

• General formula for alkenes

• CnH2n

Which of the following is a characteristic of alkenes?

• They contain one (or more) double covalent bonds.

• They are less reactive than alkanes.

• They contain only single bonds.

• They are saturated hydrocarbons.

Answer explanation

Alkenes are characterized by the presence of one or more double covalent bonds, distinguishing them from alkanes, which only have single bonds. This makes the correct choice: they contain one (or more) double covalent bonds.

What type of reaction occurs when alkanes react with halogens in the presence of UV light?

• Decomposition reaction

• Addition reaction

• Combustion reaction

• Substitution reaction

Answer explanation

When alkanes react with halogens in the presence of UV light, a substitution reaction occurs. This involves the replacement of a hydrogen atom in the alkane with a halogen atom, forming a haloalkane.

Match the following compounds with their classification.

• Alkane

• Propene

• Alkene

• Ethyne

• Alkene

• Ethene

• Alkyne

• Butane

Match the following products with the correct substances produced during the complete combustion of methane.

• Carbon dioxide and soot

• Hydrogen and carbon dioxide

• Hydrogen and carbon dioxide

• Carbon dioxide and water

• Water and carbon dioxide

• Soot and carbon dioxide

• Water and carbon monoxide

• Carbon monoxide and water

Longer chain hydrocarbons have (a)   .

• More flammable

• Less viscous

• Higher boiling point

• Lower boiling point

Answer explanation

Longer chain hydrocarbons have higher boiling points due to increased molecular weight and stronger van der Waals forces, which require more energy to break. This is why the correct answer is 'Higher boiling point'.

What is the process called that separates crude oil into different fractions?

• Evaporation

• Filtration

• Distillation

• Cracking

Answer explanation

The process that separates crude oil into different fractions is called distillation. This method uses heat to vaporize the oil, allowing different components to condense at various temperatures, effectively separating them.

Incomplete combustion produces (a)   .

• Oxygen

• Carbon dioxide

• Water

• Carbon monoxide

Answer explanation

Incomplete combustion occurs when there is insufficient oxygen, leading to the production of carbon monoxide instead of carbon dioxide. Thus, the correct answer is carbon monoxide.

What is the main danger of carbon monoxide?

• It is a greenhouse gas.

• It causes acid rain.

• It is highly flammable.

• It can cause suffocation.

Answer explanation

The main danger of carbon monoxide is that it can cause suffocation. It binds to hemoglobin in the blood, preventing oxygen transport, which can lead to serious health issues or death.

Most of the compounds in crude oil are (a)   .

• Alkenes

• Alkynes

• Alkanes

• Aromatics

Answer explanation

Most compounds in crude oil are alkanes, which are saturated hydrocarbons consisting of carbon and hydrogen. They form the largest portion of crude oil, making 'Alkanes' the correct choice.