Organic Chemistry – Hydrocarbons, Alkenes, Alcohols & Polymers

44 question-and-answer flashcards summarising key definitions, processes and reactions from the lecture on organic chemistry.

What information does the molecular formula of a compound provide?

The actual number of each type of atom present in one molecule.

What does an empirical formula show?

The simplest whole-number ratio of the atoms in a compound.

What is a displayed formula?

A structural formula that shows every atom and every bond in the molecule.

What is meant by a functional group?

A specific group of atoms responsible for the characteristic chemical reactions of a compound.

Define a homologous series.

A family of compounds with the same functional group in which successive members differ by a CH₂ unit.

What is crude oil?

A complex mixture of mainly hydrocarbons formed from the remains of ancient marine organisms.

Why can fractional distillation separate crude oil?

Its components have different boiling points, allowing them to condense at different heights in the fractionating column.

Why does temperature decrease as you move up a fractionating column?

The column is designed with a negative temperature gradient so vapours cool as they rise.

Which fraction has the lowest boiling point and where is it collected?

Refinery gas, collected at the very top of the column.

Give two everyday uses of refinery gas.

Cooking/household gas and fuel for portable heaters; also used as chemical feedstock.

What is the main use of petrol (gasoline)?

Fuel for cars and small vehicles.

State one common use of kerosene.

Jet aircraft fuel.

Which fraction provides fuel for large ships and industrial furnaces?

Heavy fuel oil.

Why does bitumen remain at the bottom of the fractionating column?

It has a very high molecular mass and boiling point, so it does not vaporise.

How does chain length affect the boiling point of hydrocarbons?

Longer chains have stronger intermolecular forces, giving higher boiling points.

What is meant by a saturated hydrocarbon?

A molecule containing only single carbon–carbon bonds.

Give the general formula of alkanes.

CₙH₂ₙ₊₂.

Name the alkane with five carbon atoms.

Pentane.

Write the balanced equation for complete combustion of propane.

C₃H₈ + 5O₂ → 3CO₂ + 4H₂O.

What two harmful products may form during incomplete combustion of an alkane?

Carbon monoxide (CO) and carbon (soot).

Give the general formula of alkenes.

CₙH₂ₙ.

What functional group characterises an alkene?

A carbon–carbon double bond, C=C.

Why are alkenes described as unsaturated?

They contain at least one C=C bond and can add more atoms across it.

What colour change occurs when an alkene is shaken with bromine water?

The orange bromine water is decolourised (turns colourless).

Write the word equation for hydrogenation of ethene.

Ethene + hydrogen → ethane.

State typical conditions for alkene hydrogenation.

Nickel or platinum catalyst and about 150 °C.

What product is formed when ethene reacts with steam?

Ethanol.

List the conditions required for hydration of ethene.

High temperature, high pressure and a phosphoric acid catalyst.

Why do addition reactions of alkenes have 100 % atom economy?

All atoms of the reactants become part of the single organic product; no by-product is formed.

Write the balanced fermentation equation that produces ethanol.

C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂.

State two essential conditions for fermentation.

Warm temperature (25–40 °C) and absence of oxygen.

Give one advantage of producing ethanol by fermentation.

Low energy requirement / uses renewable biomass / considered carbon neutral.

Give one disadvantage of fermentation as an industrial route to ethanol.

Process is slow, produces impure ethanol, low atom economy, and competes with food crops for land.

Write the chemical equation for the hydration route to ethanol.

C₂H₄ + H₂O → C₂H₅OH.

Name one advantage of ethanol production by hydration of ethene.

Very fast reaction that produces pure ethanol with 100 % atom economy.

Name one disadvantage of hydration of ethene.

High energy demand and reliance on non-renewable ethene from crude oil.

What type of reaction produces an ester from an alcohol and a carboxylic acid?

Condensation (esterification).

Write the word equation for methanol reacting with pentanoic acid.

Methanol + pentanoic acid → methyl pentanoate + water.

During condensation polymerisation, what small molecule is commonly eliminated?

Water (H₂O).

Which two functional groups react to form a polyester?

Diol (–OH groups) and dicarboxylic acid (–COOH groups).

Which two functional groups react to form a polyamide?

Diamine (–NH₂ groups) and dicarboxylic acid (–COOH groups).

Give two differences between addition and condensation polymerisation.

Addition uses one alkene monomer and forms no by-product with 100 % atom economy, whereas condensation uses two (or more) different monomers and releases a small molecule like water, so atom economy is <100 %.

Why are longer alkane molecules less volatile than shorter ones?

They have stronger intermolecular forces, so more energy is