Alkanes

Question 1

What are alkanes?

Answer 1

• Alkanes are saturated hydrocarbons.

Question 2

General formula for alkanes

Answer 2

CₓH₂ₓ₊₂

Question 3

General formula for cycloalkanes. Are they saturated hydrocarbons?

Answer 3

-CₓH₂ₓ
Yes, they are saturated hydrocarbons (as there are no C=C double bonds.)

() - extra info for clarification.

Question 4

What is another word for crude oil?

Answer 4

• Petroleum.

Question 5

What is crude oil/ petroleum?

Answer 5

• Mixture of different length hydrocarbons- mainly alkane hydrocarbons.

Question 6

How can hydrocarbons in petroleum/ crude oil be separated? What are the stages of this separation?

Answer 6

• By fractional distillation.
  1.) Crude oil vapourised
  2.) Vapourised oil enters column and rises.
  3.) Column has temperature gradient. As vapour rises, parts of mixture condense at different temperatures.
  4.) This is because there are different chain lengths - hence, different boiling points.
  5.) The fractions are drawn off at different levels.

Question 7

What happens to the longest and shortest hydrocarbons during fractional distillation?

Answer 7

• Longest hydrocarbons: don’t vapourise and run down to bottom of column.
• Shortest hydrocarbons: won’t even condense at top of column; so come off as a gas at top of column.

Question 8

What is cracking?

Answer 8

• Cracking is breaking a longer chain alkane into shorter hydrocarbons.
• It involves breaking the C-C bond in alkanes.

Question 9

Why is cracking useful?

Answer 9

• Because shorter hydrocarbons are in higher demand than longer hydrocarbons - as they are used as fuel.

Question 10

What are the two different types of cracking?

Answer 10

• Thermal cracking
• Catalytic cracking.

Question 11

What are conditions for thermal cracking? What does thermal cracking produce predominantly? Why is the product useful ?

Answer 11

• High temperature and high pressure required: 1000⁰C/ 70 atm
• Thermal cracking produces a high percentage of alkenes - useful as alkenes can be used to make polymers (ie. plastics.)

Question 12

What are the conditions for catalytic cracking?

Answer 12

• High temperature of 450⁰C
• Slight pressure
• Zeolite catalyst

Question 13

What is the role of the zeolite catalyst in catalytic cracking?

Answer 13

• Helps lower the temperature and pressure needed for cracking to occur.
• This lowers the cost and speeds up the process.

Question 14

What are the main products of catalytic cracking?

Answer 14

• Aromatic hydrocarbons (useful in fuels in vehicles) and motor fuels.

Question 15

What are alkanes predominantly used as, and why?

Answer 15

• Alkanes are used as fuels because most burn readily to produce large amounts of energy.

Question 16

What are the products for the complete combustion of alkanes?

Answer 16

Carbon dioxide + water

Question 17

True or False

Only the combustion of ALKANES (specifically) can be either complete or incomplete.

Answer 17

• False.
• Combustion of alkanes AND other organic compounds can be complete or incomplete.

Question 18

What is complete vs incomplete combustion?

Answer 18

• Complete: fuel burns in plentiful supply of oxygen.
• Incomplete: fuels burns in limited supply of oxygen.

Question 19

What are the products for incomplete combustion of alkanes?

Answer 19

• Carbon monoxide - CO(g)
• Carbon soot - C(s)
• Unburned hydrocarbons
• Only one of these are formed in one equation, not all in same equation!

Question 20

What is the issue with carbon monoxide (CO)? How can CO be removed from exhaust fumes in the engine?

Answer 20

• CO is poisonous as it binds to haemoglobin in the blood, preventing oxygen binding.
• CO can be removed using a catalytic converter.

Question 21

3 problems associated with carbon soot.

Answer 21

1.) Causes breathing problems.
2.) Makes buildings dirty
3.) Clogs up engines.

Question 22

How is increase in carbon dioxide affecting the environment and HOW?

Answer 22

• Causing global warming.
• Carbon dioxide = greenhouse gas: absorbs infrared radiation from sun.
• All greenhouse gases CONTAIN polar bonds.

Question 23

How are oxides of nitrogen (NOx) formed/ made?

Answer 23

• Oxygen and nitrogen (naturally in the air) combine/ react due to high pressures and temperatures in car engines.

Question 24

Give 4 poulltants produced from the internal combustion engines.

Answer 24

1.) NOx (oxides of nitrogen.)
2.) CO
3.) Carbon (soot)
4.) Unburned hydrocarbonds.

Question 25

What do catalytic converters do?

Answer 25

- Catalytic converters remove gaseous pollutants from internal combustion engines. - Reduce amount of unburnt hydrocarbons, oxides of nitrogen going into atmosphere/ STOP CO from entering the atmosphere.

Question 26

What is ozone? Where does it occur? What is the issue with ozone?

Answer 26

- Ozone occurs in lowest level of atmosphere. - Sunlight, hydrocarbons and nitrogen dioxide mix to form ozone. - Ozone is toxic to humans.

Question 27

How is photochemical smog formed?

Answer 27

- Solid carbon soot and ozone mix to make photochemical smog.

Question 28

What does combustion of hydrocarbons containing sulphur lead to?

Answer 28

- Combustion of hydrocarbons containing sulphur leads to sulphur dioxide - that causes air pollution/ acid rain.

Question 29

How does sulphur dioxide actually cause acid rain? What other gases will cause acid rain like sulphur dioxide does?

Answer 29

- Sulphur dioxide = acidic gas. - Reacts with water vapour (in atmosphere) to form sulphuric acid/ acid rain. - Oxides of nitrogen will cause acid rain like sulphur dioxide does.

Question 30

What 3 main problems does acid rain cause?

Answer 30

1.) Causes damage to plants. 2.) Kills fish 3.) Causes erosion of buildings.

Question 31

How do you remove sulphur dioxide from flue gases in factories? What is this process called?

Answer 31

- Process called: wet-scrubbing. - Alkali - calcium carbonate/ oxide- will be dissolved in water and sprayed on acidic sulphur dioxide gas, neutralising the sulphur dioxide.

Question 32

What are the different fractions collected by fractional distillation? Give the order the different fractions are collected in, starting from the top- working you way down the column. ## Footnote Neumonic to remember?

Answer 32

1.) LPG: liquid petroleum gases. 2.) Petrol/ Gasoline 3.) Naptha 4.) Kerosene 5.) Diesel oil 6.) Fuel oil 7.) Bitumen ## Footnote Lazy Penguings, Never Keep drinking flipping beer.

Question 33

What are the different uses for all the fractions obtained from crude oil by fractional distillation?

Answer 33

1.) LPG --> Bottled gases (ie. stove gases.) 2.) Petrol/ Gasoline --> fuel for cars 3.) Naptha --> used in petrochemical industry e.g., paints. 4.) Kerosene --> jet fuel 5.) Diesel oil --> fuel for vans/ lorries 6.) Fuel oil --> fuel for ships. 7.) Bitumen --> used for road surfacing.

Question 34

Definition of "fraction" formed in fractional distillation.

Answer 34

- Fraction is a mixture of compounds with similar boiling points.

Question 35

# June 2023 Paper 2 AS Explain why water should enter the condenser at the bottom and not at the top.

Answer 35

- Ensures that the condenser fills with water. - Ensuring more vapours condense.

Question 36

# 2016 Paper 2 AS Platinum, rhodium, palladium are metals used inside catalytic converters. Very thin layer of metals is used on honeycomb ceramic support. Explain why thin layer is used in this way.

Answer 36

- Increases surface area. - Reduces amount of metal needed.

Question 37

Write two equations/ reactions that happen in catalytic converter.

Answer 37

- CO + NO --> CO₂ + ½N₂ - C₈H₁₈ + 25NO --> 8CO₂ + 9H₂O + 25/2N₂

Question 38

3 equations/ reactions that occur in internal combustion engine.

Answer 38

- N₂ + O₂ --> 2NO - NO + ½O₂ --> NO₂ - 2NO₂ + ½O₂ + H₂O--> 2HNO₃

Question 39

Where does water go in and out in condenser of fractional distilation?

Answer 39

- Water in: from bottom. - Water out: from top.

Question 40

# June 2024 paper 2 Compound L (Mr 88) contains C, H, O only. 6.56x10^-4mol sample of L burns completely in air to form 2.62x10^-3 mol of water and 2.62x10^-3 mol of carbon dioxide. Deduce formula of L.

Answer 40

- Make the moles in simplest whole number ratio 1:4:4 - C4H8 and then work out how many O's from Mr (88.) - C4H8O2!!