Topic 20 - Fuels Flashcards
8.1 - What are hydrocarbons?
A hydrocarbon is a compound that contains hydrogen and carbon atoms only.
A carbon atoms can form four covalent bonds to hydrogen, so the compounds can vary in its number of carbons.
8.2/15 - What is crude oil?
Crude oil is a complex mixture of hydrocarbons that is formed from the fossils of living things and contain carbon atoms in chains or ring structures.
Natural gas and crude oil are finite resources as they are made slower than the amounts humans use.
It is useful for fuels in vehicles and raw materials in the petrochemical industry ( substances made of crude oil ).
Hydrocarbons can exist in different states, depending on their size and complexity, crude oil at room temperature is a liquid.
8.3 - Explain the separation of crude oil into simpler hydrocarbons
The separation happens in a fractionating column, where crude oil is heated and evaporated, this is done because crude oil isn’t ignited easily.
The column is hottest at the bottom and coldest at the top, the vapours condense when it reaches a part in the column below their boiling point.
Liquids in the middle fall into trays, vapours with low boiling points don’t condense and are left at the top while substances with high boiling points leave the bottom of the column as a hot liquid.
8.4 - Describe the names and uses of the oil fractions
Oil fractions are parts of crude oil that are separated into liquids and gases.
Gases are used in domestic heating and cooking.
Petrol is used as fuel in cars.
Kerosene is used as fuel for aircrafts.
Diesel oil is used as fuel for cars and trains.
Fuel oil is used for large ships and power stations.
Bitumen is used for surface roads and roofs.
8.5 - Explain how hydrocarbons in different fractions differ
Hydrocarbons is similar fractions have similar number of carbon and hydrogen and aren’t pure.
The fraction with gases have short hydrocarbons of 1-4 carbon atoms, low boiling points, easily ignited and high viscosity ( how easily it flows ).
As you go down the fractions, there are longer hydrocarbons, high boiling points, difficult to ignite and low viscosity.
In crude oil, the fractions are mostly part of the alkane homologous series.
8.6 - Explain the homologous series
There are many homologous series but they all:
Have the same molecular formulae of neighbouring compounds
Have the same general formula.
Show a gradual variation in physical properties like their boiling points.
They have similar chemical properties.
8.6 - Explain the alkane homologous series
Molecular formulae - compounds increase by CH2, from methane to ethane, the formula changes from CH4 to C2H6.
General formulae - C(n)H(2n+2) - the number of hydrogen atoms is twice the carbon atoms plus two.
Trends in physical properties - As the number of carbon atoms in a hydrocarbon increases, so does the boiling point.
Similar chemical properties - Alkanes have similar chemical properties, when they react with excess oxygen, CO2 and water is formed.
8.7 - What happens in the complete combustion of hydrocarbons?
Only carbon dioxide and water are produced and energy is given out.
It only happens when there is a good supply of air/oxygen.
To investigate combustion: A pump draws combustion products from a bunsen burner.
Iced water cools the water vapour through the tube.
White anhydrous copper sulfate in the tube forms blue hydrated copper sulfate, showing presence of water.
Limewater in the boiling tube turns milky, showing presence of CO2.
8.8 - Explain what incomplete combustion of hydrocarbons produces
Incomplete combustion of a hydrocarbon forms water, energy, carbon monoxide and carbon.
This happens in a limited supply of air/oxygen.
This can lead to some carbon not being fully oxidised like CO2 and partially oxidise to form CO and not oxidised to form carbon soot.
8.9 - Explain how carbon monoxide is toxic
CO is a toxic gas, because it binds to haemoglobin in red blood cells to prevent oxygen binding.
This reduces the amount of oxygen carried and causes people to feel sleepy and become unconscious.
High CO poisoning can also cause death.
8.10 - Describe the problems caused by incomplete combustion
CO used in boilers and heaters can cause problems when poorly maintained.
Soot can block pipes carrying waste gases away from appliances, blackening buildings and breathing problems.
8.11 - Explain how impurities in hydrocarbon fuels result in the production of sulfur dioxide
Hydrocarbon fuels may contain sulfur compounds. These are natural impurities which are mostly removed.
When a hydrocarbon is burnt, the sulfur reacts with the oxygen in the air to form sulfur dioxide gas (SO2).
8.12 - Explain some problems with the production of sulfur dioxide
Sulfur dioxide dissolves in the water in clouds to form a mixture of acids like sulfurous acid. H2O + SO2 –> H2SO3
Sulfurous acid is oxidised to form sulfuric acid. H2SO3 + O2 –> H2SO4
The mixture of sulfurous acid and sulfuric acid causes problems when it falls as acid rain.
Crops don’t grow well when soil is too acidic.
Acidity can kill fish and insects in rivers.
Acid rain increases weathering of buildings made of limestone and breaks its structure. calcium carbonate + sulfuric acid –> calcium sulfate + water + CO2
Acid rain also corrodes metals faster, weakening them.
8.13 - Explain how oxides of nitrogen are made
Car engines are combustion engines, where fuel is mixed with air and ignited inside it.
The ignition causes temperatures to be high enough for the nitrogen and oxygen in the air to react to produce nitrogen oxides.
These oxides are pollutants and can cause acid rain.
This is because nitrogen dioxide forms dilute nitric acid when dissolved in clouds.
NO2 is a toxic red gas which can cause respiratory disease.
Catalytic converters in cars convert most oxides into harmless nitrogen.
8.14 - Evaluate why hydrogen is a better fuel source than petrol for cars
Petrol is in high demand as a fuel. It is liquid at room temperature so can bed stored in a car’s fuel tank and pumped into the engine.
Petrol is easily ignited and its combustion releases high amounts of energy.
Hydrogen can also be used to fuel cars. It is a by product of cracking and can be produced by reaction methane with steam.
The combustion of hydrogen produces water vapour and no CO2.
This is good as CO2 is a greenhouse gas, linked to global warming.
Hydrogen is easily ignited and releases high amounts of energy.
But it is a gas at room temperature, making it difficult to store in large amounts.
