organic chem; alkanes

Question 1

Alkanes

Answer 1

Are saturated hydrocarbons

Question 2

Hydrocarbon

Answer 2

Molecule containing ONLY hydrogen & carbon

Question 3

General formula for cycloalkanes

Answer 3

CnH2n

Question 4

Cycloalkane

Answer 4

Are saturated & are a functional group isomer of alkenes

Question 5

Where are alkanes found?

Answer 5

In crude oil

Question 6

Crude oil

Answer 6

It’s a mixture of different length hydrocarbons

Question 7

Fractional distillation

Answer 7

Vaporised oil enters the column & rises through the trays — the longest hydrocarbons don’t vaporise & run down to the bottom

Question 8

Describe the column of fractional distillation

Answer 8

The column has a temp gradient — its cooler at the top. As the vapour rises, parts of the mixture condense at different temps

Question 9

Why do some hydrocarbons condense at different temps?

Answer 9

As they have different chain lengths (& boiling points)

Question 10

Fractional distillation for the shortest hydrocarbons

Answer 10

They come off as a gas at the top of the column

Question 11

Products of fractional distillation (in order)

Answer 11

Gas — stove gas
Petrol — cars
Kerosene — jet fuel & heating
Diesel oil — fuel
Fuel oil — ships & power stations

Question 12

Cracking

Answer 12

It’s the process of breaking a longer chain alkane to shorter hydrocarbons

Question 13

Types of cracking

Answer 13

Thermal & Catalytic

Question 14

Thermal Cracking

Answer 14

Conditions: high temp (1000˚C) & high pressure (70 atm)
Products: mainly alkenes

Question 15

What are the products of thermal cracking used for?

Answer 15

Alkenes are used to make polymers (e.g. plastics)

Question 16

Catalytic cracking

Answer 16

Conditions: High temp (450˚C) & slight pressure used & zeolite catalyst
Products: Mainly aromatic hydrocarbons, useful in fuels

Question 17

Why is a catalyst used for catalytic cracking?

Answer 17

As it lowers the temp & pressure needed for cracking for — lowers cost & speeds up the process

Question 18

Complete combustion of alkane

Answer 18

Alkanes burn in oxygen completely to produce carbon dioxide & water

Question 19

Why are alkanes a good fuel?

Answer 19

Are good fuel as most burn readily to produce large amounts of energy

Question 20

Uses of alkanes

Answer 20

Used to power vehicles & electricity

Question 21

Incomplete combustion of alkenes

Answer 21

When alkanes burn with a limited supply of oxygen, carbon monoxide & carbon (soot) is produced

Question 22

Effects of carbon monoxide

Answer 22

It’s poisonous as it bonds to haemoglobin in the blood & prevents oxygen bonding — can be removed using a catalytic converter

Question 23

Effects of soot

Answer 23

Can cause breathing problems, makes buildings dirty & clog ups engines

Question 24

Product of burning fossil fuel

Answer 24

Carbon dioxide — greenhouse gas

Question 25

Greenhouse effect

Answer 25

This is where carbon dioxide absorbs infra red radiation (heat) from the sun but emit some of it back in to earth

Question 26

Effects of photochemical smog

Answer 26

Harms the respiratory system in animals & damages plants

Question 27

Formation of ozone

Answer 27

Ozone occurs at the lowest level of the atmosphere which exists as sunlight, hydrocarbons and nitrogen dioxide mix to from ozone

Question 28

How is a photochemical smog formed?

Answer 28

Formed when solid carbon particulates & ozone mix

Question 29

Formation of nitrogen dioxide gas

Answer 29

Oxide of nitrogen & oxygen found in the air combine under high pressure & temp — car engines provide these conditions

Question 30

Importance of catalytic converters

Answer 30

Help to reduce the amount of unburnt hydrocarbons & oxides of nitrogen going into the atmosphere

Question 31

Effect of burning fossil fuels

Answer 31

Can release sulfur dioxide which contributes to acid rain

Question 32

Effects of acid rain

Answer 32

Causes damages to plants, kills fish & causes erosion of buildings

Question 33

How is sulfur dioxide produced?

Answer 33

Some fossil fuels contain sulfur based impurities, so when burned the sulfur reacts with oxygen producing sulfur dioxide

Question 34

Formation of acid rain

Answer 34

Sulfur dioxide is an acidic gas so when it reacts with water in the atmosphere it forms sulfuric acid, which falls as acid rain — nitrogen oxides have the same effect

Question 35

Wet scrubbing

Answer 35

Process that removes sulfur dioxide from flue gases by using an alkali to neutralise the sulfur dioxide in flue gases

Question 36

What substances does wet scrubbing use?

Answer 36

Involves dissolving calcium carbonate or oxide in water & spraying it on acidic sulfur dioxide gas

Question 37

Stages of free radical chain reaction

Answer 37

Initiation Propagation Termination