SC20-21

Question 1

What is crude oil separated into?

Answer 1

Different hydrocarbon fractions

Question 2

What is the main source of hydrocarbons?

Answer 2

Crude oil

Question 3

How is crude oil formed?

Answer 3

It’s formed underground, over millions of years (at high temperatures and pressures) from the buried remains of plants and animals.

It’s non-renewable (finite), so one day it will run out.

Question 4

What is crude oil?

Answer 4

It’s a complex mixture of lots of different hydrocarbons

Question 5

What is a hydrocarbon?

Answer 5

It’s compounds which contain just hydrogen and carbon.

Question 6

What is the formations of hydrocarbons in crude oil?

Answer 6

They have their carbon atoms either arranged in rings or chains.

They’re mostly alkanes.

Question 7

What are fractions?

Answer 7

Simpler, more useful mixtures containing groups of hydrocarbons.

Question 8

How is crude oil separated into different fractions?

Answer 8

Fractional distillation.

Question 9

what happens in fractional distillation?

Answer 9

The oil is heated until most of it has turned to gas. The gases enter a fractionating column.

In the column there’s a temperature gradient. (Its hot at the bottom and gets colder at the top).

The longer hydrocarbons have higher boiling points. They turn back into liquids and drain out of the column early on, when they’re near the bottom. And the shorter hydrocarbons have lower boiling points so drain out nearer the top.

Question 10

Name the different fractions?

Answer 10

Bottom to top -

Bitumen 
Fuel
Diesel
Kerosene 
Petrol
Gases

Question 11

What are the uses for -

Bitumen 
Fuel
Diesel
Kerosene 
Petrol 
Gas

Answer 11

1. Surface roads and roofs.
2. Fuel for large ships and also some power stations.
3. Fuel in some cars and larger vehicles (trains).
4. Aircrafts
5. Cars
6. Domestic heating and cooking.

Question 12

What are homologous series?

Answer 12

Its a group (family) of molecules which have the same general formula and share similar chemical properties.

Question 13

Name two different homologous series?

Answer 13

Alkanes

Alkenes

Question 14

Name some hydrocarbons? (Alkanes)

How many carbons are in each of them?

Answer 14

1 - methane 
2 - ethane 
3 - propane 
4 - butane 
5 - pentane 
6 - hexane

Question 15

What’s the general formula for alkanes?

Answer 15

CnH2n+2

Question 16

Why do hydrocarbons make good fuels?

Answer 16

Because the combustion reactions that happen when you burn them in oxygen gives out lots of energy.

Question 17

What are the products when you burn hydrogen in plenty of oxygen?

Answer 17

Carbon dioxide and water.

This is called complete combustion.
Incomplete combustion occurs when a hydrocarbon burns in a limited supply of oxygen.

Question 18

When does incomplete combustion happen?

Answer 18

When hydrocarbons burn in a limited supply of oxygen.

Question 19

What does an incomplete combustion produce?

Answer 19

Toxic carbon monoxide and soot

Question 20

Why is carbon monoxide toxic?

Answer 20

It can combine with red blood cells and stop your blood from doing its proper job of carrying oxygen around the body.

A lack of oxygen in the blood supply tot eh brain can lead to fainting, a coma or even death.

Question 21

What does soot do?

Answer 21

Tiny particles of carbon can be released into the atmosphere. When they fall back to the ground, the deposit themselves as the horrible black dust we call soot.

Soot makes buildings look dirty, reduces it quality and can cause or worsen respiratory problems.

Question 22

What does sulphur dioxide cause?

Answer 22

Acid rain.

Question 23

How does sulphur dioxide cause acid rain?

Answer 23

Sulfur dioxide comes from suffer impurities in the fossil fuels.

When sulfur dioxide mixes with clouds, it forms dilute sulfuric acid. This then falls as acid rain.

Question 24

What can acid rain do?

Answer 24

Causes lakes to become acidic and many pants and animals die as a result.
Kills trees, damages limestone buildings and stone statues and can also make metal corrode.

Question 25

How are nitrogen oxides created?

Answer 25

From a reaction between nitrogen and oxygen in the air, caused by the energy released by combustion reactions, for example in the internal combustion engines of cars.

Question 26

What do nitrogen oxides cause?

Answer 26

They’re harmful pollutants. They can contribute to acid rain and, at ground level, can cause photochemical smog.

Question 27

What is photochemical smog?

Answer 27

Its a type of air pollution that can cause breathing difficulties, headaches and tiredness.

Question 28

What are the pros of using hydrogen as a fuel?

Answer 28

Its a very clean fuel. The only waste product is water as the hydrogen reacts with oxygen. Hydrogen is obtained from water which is a renewable resource, so it wont run out.

Question 29

What are the cons of using hydrogen as a fuel?

Answer 29

You need a special expansive engine. Needs to be manufactured which is expensive and often uses energy from another source (fossil fuels). Its hard to store so isn’t widely available.

Question 30

What is cracking?

Answer 30

Splitting up long chain hydrocarbons.

Question 31

What does cracking do?

Answer 31

Turns long saturated (alkane) molecules into smaller unsaturated (Alkene) and alkane molecules (which are more useful). Its a form of thermal decomposition

Question 32

What is thermal decomposition?

Answer 32

One substance breaks down into at least two new ones when you heat it. This means breaking strong covalent bonds, so you need lots of energy. A catalyst is often added to speed things up.

Question 33

What is the theory for how the atmosphere has evolved?

Answer 33

Phase 1 - volcanoes gave out steam and CO2. Phase 2 - green plants evolved and produced oxygen. Phase 3 - ozone layer allows evolution of complex animals.

Question 34

What is phase 1 of the atmosphere?

Answer 34

The wrath’s surface was originally molten for many millions of years. There was almost no atmosphere. Eventually the earths surface cooled and a thin crust formed, but volcanoes kept erupting, releasing gases from inside the earth. It released mainly CO2. When things eventually settled down, the early atmosphere was mostly CO2, and water vapour. There was very little oxygen. The water vapour later condensed to form the oceans.

Question 35

What is phase 2 of the atmosphere?

Answer 35

A lot of the early CO2 dissolved into the oceans. Nitrogen gas was then put into the atmosphere in two ways - it was formed by ammonia reacting with oxygen, and was released by bacteria. Nitrogen wasn’t very reactive. So the amount of N2 in the atmosphere increased, because it was being made but not broken down. Next, green plants evolved over most of the earth. As they photosynthesised, they removed CO2 and produced oxygen. Due to the plants the amount of oxygen in the air gradually increased and much of the CO2 eventually got locked up in fossil fuels and sedimentary rocks.

Question 36

What is phase 3 of the atmosphere?

Answer 36

The build up of oxygen in the atmosphere killed off early organisms that couldn’t tolerate it, but it did allow the evolution of more complex organisms that made use of the oxygen. The oxygen also created the ozone layer, which blocked harmful rays from the sun and enabled vein more complex organisms to evolve. There is virtually no CO2 left now.

Question 37

How is human activity affecting the composition of air?

Answer 37

CO2 levels are increasing. 1. The human population is increasing, so there is more people respiring, giving out CO2. 2. Mor people means that more energy is being used (heating, lighting). 3. More people also means more more land is needed to build houses and grow food. This space is often made by chopping down trees, which results in less things to take CO2 out of the atmosphere. 4. CO2 is also produced by volcanoes erupting.

Question 38

How does the greenhouse effect help keep the earth warm?

Answer 38

1. The sun gives out electromagnetic radiation. 2. Some electromagnetic radiation, at most wavelengths, passes through the atmosphere. 3. The ER with short wavelengths is absorbed by the earth - warming it. 4. If the concentration of greenhouse gases in the atmosphere increases, you get an enhanced greenhouse effect. This is where more heat radiation from the earth is absorbed and less re-emitted back into space. This causes the atmosphere to heat up.

Question 39

Why is historical data not as accurate?

Answer 39

Less data was taken over fewer locations and the methods used to collect the data were less accurate.

Question 40

How can you estimate past data?

Answer 40

Analyse fossils, tree rings or gas bubbles trapped in ice sheets to estimate past levels of atmospheric carbon dioxide. However they’re much less precise than current measurements and also much less representative of global levels.