Hydrocarbons

Question 1

What is a hydrocarbon?

Answer 1

A hydrocarbon is any compound that is formed from carbon and hydrogen atoms only.

Question 2

What is the Homologous series?

Answer 2

A group of organic compounds that have similar chemical properties and have the same general formula.

Question 3

What are alkAnes?

Answer 3

AlkAnes are the simplest type of hydrocarbon, they are a homologous series and are saturated compounds, meaning each carbon atom forms four single covalent bonds.

Question 4

What is the general formula for alkAnes?

Answer 4

CnH2n+2

Question 5

What are the first four alkAnes?

Answer 5

Methane (CH4), Ethane (C2H6), Propane (C3H8) and Butane (C4H10).

Question 6

What are alkEnes?

Answer 6

AlkEnes are a homologous series and they are unsaturated, meaning they have a double bond between two of the carbon atoms in their chain.

Question 7

What is the general formula for alkEnes?

Answer 7

CnH2n

Question 8

What are the first four alkEnes?

Answer 8

Ethene (C2H4), Propene (C3H6), Butene (C4H8) and Pentene (C5H10).

Question 9

What do alkEnes need to undergo complete combustion?

Answer 9

A large amount of oxygen.

Question 10

Why do alkEnes undergo incomplete combustion?

Answer 10

There isn’t enough oxygen in the air for alkEnes to combust completely.

Question 11

What products are produced by incomplete combustion?

Answer 11

Carbon, carbon dioxide, carbon monoxide and water. alkEne + oxygen > carbon + carbon dioxide + carbon
monoxide + water

Question 12

What does incomplete combustion result in?

Answer 12

A smoky yellow flame, and less energy being created compared to complete combustion.

Question 13

How do the hydrocarbon properties change due to the carbon chain length?

Answer 13

The shorter the carbon chain, the less viscous (thick) the hydrocarbon. The shorter the carbon chain, the more volatile (lower boiling points) the hydrocarbon. The shorter the carbon chain, the more flammable (easier to ignite) the hydrocarbon.

Question 14

What happens when alkEnes react via addition reactions?

Answer 14

The carbon-carbon double bond will open up to leave a single bond and a new atom is added to each
carbon.

Question 15

What is hydrogenation?

Answer 15

Hydrogen can react with double-bonded carbons to open up the double bond and form alkAne. The alkEne is reacted with the hydrogen in the presence of a catalyst.

Question 16

What happens when steam reacts with alkEnes?

Answer 16

When alkEnes react with steam, water is added across the double bond and an alcohol is formed.

Question 17

What happens when halogens react with alkEnes?

Answer 17

When alkEnes react with halogens, saturated molecules are formed with the double-bonded carbons each becoming bonded to a halogen atom.

Question 18

How can bromine be used to test for alkAnes and alkEnes?

Answer 18

When bromine is added to a saturated compound (like an alkAne), no reaction will happen and it will stay bright orange. When bromine is added to an alkEne, the bromine will add across the double bond and make the bromine water colourless.