5.14 describe how lng-chain alkanes are converted to alkenes and shorter-chaiin alkanes by catalytic cracking, using silica or alumina as the atalyst and a temperature in the range of 600-700°C

If carrying out the reaction in a lab...
1- Heat the hydrocarbon (e.g. paraffin).
2- After a few seconds, move the Bunsen burner to heat the silica/aluminium catalyst
3- Alternate between the two until the paraffin vaporises and the catalyst glows red
4- The heated paraffin vapour cracks as it passes over the heated catalyst
5- small alkanes collect at the end of the boiling tube, while alkene gases travel down the delivery tube
6- The alkenes are collected through water using a glass jar


In industry, vapourised hydrocarbons are passed over a powdered catalyst at about 600-700°C. silica and aluminium are used as catalysts.

Notes credit: CGP

5.13 understand that fractional distillation of crude oil produces more long-chain hydrocarbons than can be used directly and fewer short-chain hydrocarbons than required and explain why this makes cracking necessary

Fractional distillation produces lots of long chain hydrocarbons and not many short chain hydrocarbons in relative. The short chain hydrocarbons are useful but long chain hydrocarbons are not. This means we have to break the long chain hydrocarbons into short chain hydrocarbons as demand for short chain hydrocarbons is high. This is done in a process known as cracking. This process is a form of thermal decomposition, which just means breaking down the molecules into simpler molecules by heating them.

5.12 understand that nitrogen oxides and sulfur dioxide are pollutant gases which contribute to acid raid, and describe the problems caused by acid rain

Sulfur dioxide mix with clouds forming dilute sulfuric acid, which is very acidic. Nitrous oxide also mixes with clouds, forming nitric acid. These fall as acid rain which causes lakes to become acid in (killing plants and animals), kills trees and damages limestone buildings and statues.

There have also been links made between acid rain and human health although these are not proven.

5.11 understand that, in car engines, the temperature reached is high enough to allow nitrogen and oxygen from air to react, forming nitrogen oxides

In car engines, crude oil fractions (such as diesel or petrol) are burnt (as fuels). When fossil fuels are burnt, nitrogen oxide and sulfur dioxide are always released, always. When the temperature is high enough, the nitrogen and oxygen in the air react (this creates nitrous oxides, such as nitrogen monoxide and nitrogen dioxide).

NOTE: remember nitrogen oxide and sulfur dioxide are always produced when fossil fuels are burnt.

5.10 understand that incomplete combustion of fuels may produce carbon monoxide and explain that carbon monoxide is poisonous because it reduces the capacity of the blood from air to react, forming nitrogen oxides

First of all, incomplete combustion just means that the substance/thing was burnt without lots of oxygen present. When hydrocarbon fuels (for example gas or petrol) is burnt without oxygen, carbon monoxide is produced (as apposed to carbon dioxide, with complete combustion). This is bad because carbon monoxide is poisonous. This is because it combines with haemoglobin (this carried oxygen in your blood), preventing as much oxygen to get to your cells (as less oxygen can bind with the haemoglobin as there is lots of carbon monoxide combined with the haemoglobin). Therefore, less oxygen is being carried around your body (in your blood), this can lead to fainting, a coma or even death (in severe circumstances) as your cells are effectively being starved of oxygen.

5.9 describe the trend in boiling point and viscosity of the main fractions

The lower the boiling point, the lower the viscosity, and vice versa (high boiling point = high viscosity)

NOTE: basically, the lower the viscosity, the thinner the substance runs, the higher the viscosity, the thicker something is (as liquid). For example, water has a super low viscosity, whilst syrup has a higher viscosity than water.

5.8 recall the names and uses of the main fractions obtained from crude oil: refinery gases, gasoline, kerosene, diesel, fuel oil and bitumen

Refinery gases - used in pottery and glass manufacture, heating and bottled gas

Gasoline - used for fuel for cars (its petrol, in other words)

Naphtha - Used as a starting material of making things like plastics,dyes, drugs, explosives and paints (to name a few)

Kerosene - used to fuel jets, in heating and in paint solvents

Diesel - fuel for cars, trucks, trains and boats

Fuel oil - central heating and fuel for really big ships

Bitumen - used to surface roads

5.7 describe and explain how the industrial process of fractional distillation separates crude oil into fractions

NOTE: the process of fractional distillation is mentioned in point 1.7

One use of fractional distillation is separating crude oil into fractions (compounds). Heres how it happens...

- Heat the crude oil until almost all of it has turned into gas, these gases will enter the fractioning column as they evaporate. NOTE: the left over liquid is bitumen, it has a very high boiling temperature so is instead tapped off at the bottom of the column.
- NOTE: in the column there is a temperature gradient. Basically, it is really hot at the bottom and quite bit colder in the top (not actually cold though). This is useful as the substances that make up crude oil have different boiling temperatures, when the substance meets the part of the tube where it is cooler than their boiling temperature, they will condense and drain off down a tube. (NOTE: hydrocarbons with short carbon chains have a low boiling point, so they condense near the top of the fractioning column whilst hydrocarbons with long carbon chains have high boiling points, so they condense near the bottom of the fractioning column.
- This means you result with the different fractions of crude oil (each fraction contains a mixture of hydrocarbons with similar boiling points).

5.6 understand that crude oil is a mixture of hydrocarbons

Hydrocarbons are molecules which contain only hydrogen and carbon atoms. Crude oil is made up of only hydrocarbons (but lots of different types of them).