Chapter 9 - 11

Question 1

Crude oil and hydrocarbons

Answer 1

• Crude oil is a naturally occurring product
• Produce products like petrol, solvents and detergents
• A mixture of long-chain molecules made up of hydrogen and carbon only.
• The chains are called hydrocarbons
• The use of hydrocarbon is determined by the number of carbons in its chain as its properties depend on how long it is.

Question 2

Chain length molecules

Answer 2

• Can be separated using fractional distillation
• The crude oil mixture enters a tall column and is heated to a high temperature so that most of the molecules are vapourised
• The column is cooler at the top than it is at the bottom
• As the gaseous molecules rise up to the column they condense when they reach boiling point
• They are then collected and removed
• The separated sample is called fractions

Question 3

Chain length molecules

Answer 3

As they have fewer intermolecular forces between their chains. This means that they have lower boiling points and so they condense at lower temperatures and so remain a gas at lower temperatures.

Question 4

AlkANEs

Answer 4

• All of the hydrocarbons that we find in crude oil have single carbon-carbon bonds in their chains.
• They’re saturated (bonded to as many other atoms as possible)
• They belong to a homologous series called alkanes
• In a plentiful supply of oxygen, hydrocarbons will burn completely to produce carbon dioxide and water
• Incomplete combustion will produce solid carbon, carbon monoxide and unburnt hydrocarbon.

Question 5

Cracking

Answer 5

• To make a large amount of longer chain hydrocarbons more useful products, the chains can be broken into two short chains in a process called CRACKING
• This is an example of thermal decomposition
• Two methods that can be used to crack hydrocarbons, both processes result in the formation of two products; an alkENE and an alkANE.

Question 6

AlkENES

Answer 6

• Produced as one of the products of cracking
• The shorter chain alkene that is the desired product of cracking
• Can be used as monomers in polymerisation reactions to produce some of the plastics we use in our everyday lives.

Question 7

Products of cracking

Answer 7

• The sum of the carbon and hydrogen atoms in the two products of the cracking process must be the same as the number of atoms that you started with
• This means if we know what we started with and how many carbons are in one product we can work out what the other product is.

Question 8

Testing for alkenes

Answer 8

• To test whether a product is an alkENE or an alkANE, test a sample
• Bromine water (a brown/orange solution) is added to the sample of hydrocarbon and then shaken
• AlkANE = No change in the bromine water, remain brown/orange
• AlkENE = Bromine water will be decolourised, becomes a colourless solution
• This test works because of the more reactive nature of the alkENE due to its double bond. The bromine atoms in the bromine water will add to the carbon atoms on either side of the carbon-carbon double bond in an alkene to produce a saturated molecule.