GCSE Chemistry unit 1 chapter 4-6

Question 1

What is cracking?

Answer 1

Cracking is when fuels (made from a mixture of hydrocarbons molecules) are not efficient enough and are cracked to allow large hydrocarbon molecules to broken down into smaller ones.

Question 2

How does cracking work?

Answer 2

Cracking is thermal decomposition reaction. The first step is to heat the long chain hydrocarbon to vapourise it. Then the vapour is passed over a powdered aluminium oxide catalyst at a temperature of 700-800 Celsius.

Question 3

What does cracking make?

Answer 3

Shorter chain alkanes and alkenes.

Question 4

What is fractional distillation?

Answer 4

Fractional distillation is when crude oil (a mixture of hydrocarbons) is split into the different chain lenghths which have different properties.

Question 5

Is crude oil mostly alkanes or alkenes?

Answer 5

Alkanes.

Question 6

What is the general formula of an Alkene?

Answer 6

CnH2n+2

Question 7

What are the properties of shorter chains lengths?

Answer 7

• less viscous
• more volatile
• lower boiling point
• more flammable

Question 8

What are the uses of long chain hydrocarbons?

Answer 8

Lubricating engine parts + covering roads because its very gloopy.

Question 9

What are the uses of shorter chain hydrocarbons?

Answer 9

Petrol for cars because its easy to store and combust.

Question 10

What can cause acid rain, global warming and global dimming?

Answer 10

Burning fuels. If the fuel contains sulfur impurities it can cause acid rain. Particulates cause global dimming and CO2 causes global warming.

Question 11

What is the general formula for an alkene?

Answer 11

CnH2n

Question 12

What is different from an alkene to and alkane?

Answer 12

alkenes are not saturated with hydrogens and have a double bond.

Question 13

How can you tell a alkene from an alkane?

Answer 13

Bromine water. Alkenes decolourise the bromine water because the double bond opens up.

Question 14

How can ethene be used to make ethanol?

Answer 14

Ethene can be hydrated with steam in the presence of a catalyst.

Question 15

Why is making ethanol with ethene good?

Answer 15

Cheap process, continuous process,very pure product, faster process.

Question 16

Why is making ethanol with ethene bad?

Answer 16

Not renewable, Lots of energy needed for steam and pressure.

Question 17

How can you use sugar to make ethanol?

Answer 17

Sugar is fermented and converted to ethanol using yeast.

Question 18

Why is making ethanol by fermentation bad?

Answer 18

Doesn’t make pure ethanol, fermentation is slow, large volume of ethanol needed to make small amounts of ethanol, lots of land is needed.

Question 19

why is making ethanol be fermentation good?

Answer 19

sugar is a renewable source, carbon neutral, good for LEDC because less technology is needed.

Question 20

How can alkenes be used to make polymers?

Answer 20

joining together lots of small alkene molcules (monomers) to form very large molecules called polymers.

Question 21

Why do different polymers have different physical properties?

Answer 21

The physical properties of a polymer depend on what its made on, and the temperature and pressure of polymerisation.

Question 22

What is the main disadvantage of polymers?

Answer 22

They aren’t biodegradable. This means they are not broken down by micro-organisms. Furthermore this makes them hard to get rid of so its best to re-use them as many times as possible and then recycle them if you can.

Question 23

How are biodegradable plastics made?

Answer 23

By using granules of corn starch in the plastic, micro-organisms eat the corn starch and break the bits of plastic more quickly.

Question 24

What are light sensitive plasters?

Answer 24

A smart material. Peel the top layer off and light reduces the stickiness which prevents irritation to the skin.

Question 25

What are shape memory polymers?

Answer 25

A smart material. Polymers react to stimulus to become elactic and then return to its original shape. Cheaper than shape memory alloys.

Question 26

What is a hydrogel?

Answer 26

A smart material. It can change its structure in response to salt concentration, pH and temperature. They absorb water which makes them good for contact lenses, nappies and wound dressings.

Question 27

What is Crushing?

Answer 27

A way to extract a plant oil; a seed it squashed to release oil.

Question 28

How does distillation extract plant oils?

Answer 28

Refines the oil and removes water, solvents and impurities due to different boiling points.

Question 29

What can vegetable oils be used for?

Answer 29

In food: provide a lot of energy + other nutrients
Contain essential fatty acids
higher boiling point than water, faster cooking
gives flavour

Vegetable oils can also be used as a fuel.

Question 30

What is hydrogenation?

Answer 30

unsaturated oils and liquid at room temperature:They can be hardened by adding hydrogen in the presence of a nickel catalyst at about 60 celcius. Hydrogenated oils have a higher boiling point and foods contain them are usually cheaper and last for longer.

Question 31

What is an emulsion?

Answer 31

lots of droplets of one liquid suspended in another.

Question 32

What are the three pieces of evidence for continental drift?

Answer 32

the same types of fossilised animals and plants are found in America and & Africa.
The shapes of the coast fit together like a jigsaw puzzle.
matching rock formations and mountain ranges are found in Africa and south america.

Question 33

Why was Wegners theory not accepted?

Answer 33

because he trained as an meteorologist

because other scientists couldn’t see how the continents could move.

Question 34

Describe the crust.

Answer 34

out layer of earth; 20-60km thick made mostly of silicon, oxygen and aluminium.

Question 35

Decibel the atmosphere.

Answer 35

700km thick is a blanket of gases surrounding the earth.

Question 36

Describe the mantle.

Answer 36

a viscous semi-solid layer, 2 900km thick with convection currents moving tectonic plates which cause mountains, volcanoes and earthquakes.

Question 37

Describe the outer core.

Answer 37

1100km thick made out of liquid radioactive iron and nickel.

Question 38

Describe the inner core.

Answer 38

1300km thick. Its dense and very hot. Its solid due to the pressure and made out of iron and nickel.

Question 39

What is the primordial soup theory?

Answer 39

Urey-millar theory of where life on earth originated. found 13 types of amino acids formed in the primitive atmosphere.

Question 40

another theory is the Murchison theory, what that say?

Answer 40

that a meteor carried the amino acids and when they hit he earth they formed proteins.

Question 41

What produced the oxygen that is now in the atmosphere?

Answer 41

plant photosynthesising.

Question 42

What happened to the carbon dioxide that was in the atmosphere?

Answer 42

It was absorbed by plants and oceans and stored in rocks.

Question 43

How do we separate the mixture of gases in the atmosphere?

Answer 43

By first filtering it, then liquefying it then distilling it. However oxygen and argon has a very similar boiling point making it hard to get pure oxygen or pure argon.