Topic 8

Question 1

What are Hydrocarbons?

Answer 1

1) Hydrocarbons are compounds that contain only carbon and hydrogen.

Question 2

What is crude oil?

Answer 2

1) Crude oil is our main source of hydrocarbons.

Question 3

What crude oil used for?

Answer 3

1) It is used as a raw material to create lots of useful substances used in the petrochemical industry.

Question 4

Where is crude oil formed and how?

Answer 4

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

Question 5

Is it non- renewable or renewable?

Answer 5

1) Yes, it’s a non- renewable (finite) resource, meaning that one day it will run out.

Question 6

How are the hydrocarbons found in crude oil arranged?

Answer 6

1) The hydrocarbons found in crude oil have their carbon atoms arranged in either chains or rings and are mostly alkanes (hydrocarbons with a general formula)

Question 7

How can crude oil be separated?

Answer 7

1)Crude oil can be separated out into fractions- simpler more useful mixtures containing groups of hydrocarbons of similar lengths. The fractions from crude oil, e.g. petrol, kerosene and diesel are example of non- renewable fossil fuels.

Question 8

How is crude oil separated? (PROCESS)

Answer 8

1) The different fractions in crude oil are separated by fractional distillation. The oil is heated until most of it turned into a gas. The gases enter a fractionating column (and the liquid bit, bitumen is drained off at the bottom).
2) The longer the hydrocarbons have higher boiling point. They turn back into liquids and drain out of the column early on, when they’re near the bottom. The shorter the hydrocarbons have lower boiling points. They turn to liquid and drain out much later on, near to the top of the column where it’s cooler.
3) You end up with the crude oil mixture separated out into different fractions. Each fraction contains a mixture of hydrocarbons, mostly alkanes with similar boiling points.
4) It is very hot at the bottom of the column and cold at the top.

Question 9

What does the size of hydrocarbon determine?

Answer 9

1)The size of a hydrocarbon determine which fraction of crude oil it will separate into.

Question 10

What does each fraction contain?

Answer 10

1) Each fraction contains hydrocarbons (mostly alkanes) with similar numbers of carbon atoms, so all of the molecules in a fraction will have similar properties and behave in similar ways.

Question 11

What are the physical properties determined by (hydrocarbons)?

Answer 11

1) The physical properties are determined by the intermolecular forces that can h old the chains together.

Question 12

Why does the intermolecular force break easily in small molecules?

Answer 12

1) The intermolecular forces of attraction break a lot more easily in small molecules than they do in bigger molecules. That’s because the forces are much stronger between big, molecules than they are between small molecules.

Question 13

Why are shorter hydrocarbons easier to ignite?

Answer 13

1) Shorter hydrocarbons are easy to ignite because they have lower boiling points, so tend to be gases at room temperature. These gas mixture which bursts into flames if it comes into contact with a spark. Longer hydrocarbons are usually liquids at room temperature. They have higher boiling points are much harder to ignite.

Question 14

What is Viscosity?

Answer 14

1)Viscosity measures how easily a substance flows. The stronger the force is between hydrocarbon molecules, the harder it is for the liquid to flow. Fractions containing longer hydrocarbon have a higher viscosity- they’re thick like treacle. Fractions made up of shorter hydrocarbons have a low viscosity and are much runnier.

Question 15

What is a homologous series?

Answer 15

1) A homologous series is a family of molecules which have the same general formula and share similar chemical properties.
2) The molecular formulas of neighboring compounds in a homologous series differ by a CH2 unit.
3) The physical properties of compounds in a homologous series vary between the different molecules. For example, the bigger a molecule is, the higher boiling point will be.
4) Alkanes and alkenes are two different homologous series of hydrocarbons.

Question 16

Why do hydrocarbons make good fuels?

Answer 16

1) Hydrocarbons make great fuels because the combustion reactions that happen when you burn them in oxygen give out lots of energy- the reactions are very exothermic.
2) When you burn hydrocarbons in plenty of oxygen, the only products are carbon dioxide and water- this is called complete combustion.

Question 17

What do fossil fuels produce when they are burned?

Answer 17

1) When fossil fuels are burned, they release mostly CO2.
2) But they also releaser other harmful gases- especially sulphur dioxide and various nitrogen oxides.
3) The sulphur dioxide (SO2) comes from sulphur impurities in the fossil fuels.
4) When sulphur dioxide mixes with cloud, it forms dilute sulfuric acid. This fall as acid rain.

Question 18

What does acid rain cause?

Answer 18

1) Acid rain causes lakes to become acidic and many plants and animals die.
2) Acid rain kills trees, damaging limestone buildings and stone statues and can also make metal corrode.

Question 19

How is nitrogen oxide created?

Answer 19

1) Nitrogen oxides are created from a reaction between the nitrogen and oxygen in the air, caused by the energy released by combustion reactions, for example in the internal combustion engines for cars.

Question 20

Why is nitrogen oxide harmful?

Answer 20

1) Nitrogen oxides are harmful pollutants- they can contribute to acid rain and at ground level can cause photochemical smog.

Question 21

What is photochemical?

Answer 21

3) Photochemical smog is a type of air pollution that can cause breathing difficulties, headaches and tiredness.

Question 22

What are the pros of hydrocarbons?

Answer 22

1) Hydrogen is a very clean fuel. In a hydrogen fuel cell, hydrogen combines with oxygen to produce energy and the only waste product is water.
2) Hydrogen is obtained from water – a renewable resource- so it’s not going to run out. Hydrogen can even be obtained from the water produced by the cell when it’s used in fuel cells.

Question 23

What are the cons of hydrocarbons?

Answer 23

1) You need a special, expensive engine Hydrogen gas also needs to be manufactured which is expensive and often uses energy from another source- this energy often comes from burning fossil

Question 24

What is petrol, kerosene and diesel?

Answer 24

1) Petrol, kerosene and diesel oil are non-renewable fossil fuels obtained from crude oil and methane is a non-renewable fossil fuel found in natural gas.

Question 25

What is cracking?

Answer 25

1)It’s a form of thermal decomposition, which is when 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 used to speed things up.

Question 26

What does cracking do?

Answer 26

1) Cracking turns long saturated alkane molecules into smaller unsaturated alkene) and alkane molecules (which are more useful).

Question 27

Why are the longer molecules cracked into smaller molecules?

Answer 27

1) A lot of the longer molecules produced form fractional distillation are cracked into smaller ones because there’s more demand for products like petrol and diesel than for bitumen and fuel oil.

Question 28

What does cracking produce?

Answer 28

1)Cracking also produces lots alkene molecules, which can be used to make polymers (mostly plastics)

Question 29

What are vaporised hydrocarbons are passed over ?

Answer 29

1) Vaporised hydrocarbons are passed over powdered catalyst at about 400-700 degrees and 70 atm.

Question 30

Which catalyst is used for cracking?

Answer 30

1)Aluminium oxide is the catalyst used. The long- chain molecules split apart or ‘crack; on the surface of the bits of catalyst

Question 31

Why doesn’t the intermolecular force break easily in big molecules?

Answer 31

1)It makes sense if you think about it- even if a big molecule can overcome the forces attracting it to another molecule at a few points along its length, it’s still got lots of other places where the forces is still strong enough to hold it in place. That’s why big molecules have higher boiling point than small molecules do.