Organic Questions P2

Question

Answer

What is a hydrocarbon?

A compound made up of hydrogen and carbon atoms only.

What are alkanes?

Saturated hydrocarbons with only single covalent bonds.

What is the general formula for alkanes?

CnH2n+2

Give the first four alkanes.

Methane, ethane, propane, butane.

What are alkenes?

Unsaturated hydrocarbons with at least one carbon–carbon double bond (C=C).

What is the general formula for alkenes?

CnH2n

What is the functional group of alkenes?

C=C double bond.

How do alkenes react with bromine water?

They decolourise it (orange to colourless), showing presence of a double bond.

Are alkanes or alkenes more reactive?

Alkenes, due to the presence of a double bond.

What is crude oil?

A finite mixture of hydrocarbons found in rocks, formed from ancient biomass.

How is crude oil separated?

By fractional distillation.

How does fractional distillation work?

Crude oil is heated and vapours are separated based on boiling points in a fractionating column.

How are fractions in crude oil used?

As fuels (e.g., petrol, diesel, kerosene) or feedstock for the petrochemical industry.

What is cracking?

The breakdown of large alkanes into smaller alkanes and alkenes.

Why is cracking necessary?

To meet demand for smaller, more useful hydrocarbons like petrol and alkenes.

What are the two main methods of cracking?

Steam cracking and catalytic cracking.

What is produced from cracking?

A shorter alkane and an alkene.

What is the test for alkenes?

Add bromine water; it turns from orange to colourless.

What is the functional group of alcohols?

–OH

Give the first four alcohols.

Methanol, ethanol, propanol, butanol.

What is the general formula for alcohols?

CnH2n+1OH

How are alcohols used?

In fuels, solvents, and alcoholic drinks (ethanol).

What happens when alcohols combust completely?

They produce carbon dioxide and water.

How do alcohols react with sodium?

They produce hydrogen gas and a salt.

How do alcohols react with oxidising agents?

They form carboxylic acids.

What is the functional group of carboxylic acids?

–COOH

Give the first four carboxylic acids.

Methanoic acid, ethanoic acid, propanoic acid, butanoic acid.

What happens when carboxylic acids dissolve in water?

They form acidic solutions with a lower pH.

What is a weak acid?

An acid that only partially ionises in solution.

What happens when carboxylic acids react with carbonates?

They produce a salt, carbon dioxide, and water.

What are esters?

Compounds formed from an alcohol and a carboxylic acid.

What is the functional group of esters?

–COO–

What is the name of the reaction that forms esters?

Condensation (esterification).

What catalyst is used in ester formation?

Sulfuric acid.

What are esters used for?

Perfumes and flavourings.

What are polymers?

Large molecules made from many repeating small units called monomers.

What is addition polymerisation?

Reaction where unsaturated monomers (like alkenes) join to form a polymer with no other product.

What is the only product of addition polymerisation?

The polymer.

What is a repeating unit in a polymer?

A part of the polymer chain showing how the monomer repeats.

What is condensation polymerisation?

Reaction where monomers with two functional groups join, forming a polymer and a small molecule (e.g. water).

What small molecule is released in condensation polymerisation?

Usually water (H₂O).

How do condensation and addition polymerisation differ?

Addition uses one monomer type and forms only a polymer; condensation uses two types and forms a polymer + small molecule.

Name a natural polymer made by condensation polymerisation.

Proteins (from amino acids).

What is DNA?

A polymer made from four different monomers called nucleotides.

What is starch and cellulose made from?

Glucose monomers.

What is the required practical for organic chemistry (linked topic)?

Test for alkenes using bromine water (decoulorisation test).

What safety precautions are needed when testing with bromine water?

Wear gloves and goggles; use in a well-ventilated area or fume cupboard.