ALKANES [dchemlc]

what is the general formula of alkanes?

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Answer explanation

why are alkanes classified as saturated hydrocarbons?

• because they contain C-C single bonds only

• because they contain C=C double bonds only

• because they contain C-C triple bonds only

• because they do not have hydroxyl groups

Answer explanation

what is the chemical formula of the given compound?

• 2,3-dimethylbutane

• 2,3-dimethylpropane

• 2-ethylpropane

• 2-methyl-3-methylbut-1-ane

what is the name of the alkane with 4 carbons?

• butane

• propane

• hexane

• ethane

Answer explanation

which of the following gives the formula of an alkane with 12 carbons?

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Answer explanation

general formula of alkanes is as shown. so if n=12, 2n+2=26

therefore a carbon with 12 carbons has the formula C₁₂H₂₆

which of the following is not a gas at room temperature?

• methane

• butane

• propane

• pentane

Answer explanation

The first four alkanes are gases at room temperature

(- 25 °C}. All the other alkanes you are likely to see at International GCSE are liquids. Solids start to appear at about C₁₈H₃₈

what happens to the boiling points of alkanes as the number of carbons increase?

• boiling point increases

• boiling point decreases

• boiling point doesn’t change

• boiling point increases then decreases

Answer explanation

As the molecules become bigger, the strength of the intermolecular forces of attraction between them increases. This means that more energy has to be put in to break the attractions between one molecule and its neighbours. One effect of this is that the boiling points increase in a regular way.

Alkanes react with halogens in the presence of ____________ radiation.

Answer explanation

Alkanes react with halogens in the presence of ultraviolet radiation (UV light), for example from sunlight. A hydrogen atom in the alkane is replaced by a halogen atom. This is known as a substitution reaction because one atom has been replaced (or substituted) by a different one.

what will be produced when ethane reacts with bromine gas in the presence of UV radiation?

• bromoethane and HBr

• Chloroethane and HBr

• Bromomethane and HBr

• Bromoethane and HCl

Answer explanation

What is the type of reaction that occurs when Ethane reacts with bromine under certain conditions?

• substitution

• addition

• condensation

• elimination

Answer explanation

alkanes undergo substitution reactions with halogens under certain conditions