Organic Chemistry

Question 1

Hydrocarbons

Answer 1

Compound formed from carbon + hydrogen atoms only

Question 2

Types of hydrocarbons

Answer 2

• alkanes
• alkenes

Question 3

Alkanes

Answer 3

• simplest type of hydrocarbon
• have all single bonds
• have C-C bonds
• have C-H bonds

Question 4

General formula for alkanes

Answer 4

CₙH₂ₙ₊₂

Question 5

What type of series are alkanes

Answer 5

Homologous series

Question 6

Homologous series

Answer 6

Groups of organic compounds that react in similar ways and have similar properties - includes alkanes + alkenes

Question 7

Organic compounds

Answer 7

Compounds containing carbon atoms

Question 8

Why are alkanes saturated compounds

Answer 8

Each carbon atom forms 4 single covalent bonds

Question 9

First 4 alkanes

Answer 9

• methane
• ethane
• propane
• butane

Question 10

What is a displayed formula

Answer 10

Drawing showing all atoms + bonds in molecule

Question 11

Properties influencing how hydrocarbons are used for fuels

Answer 11

• viscosity
• boiling point
• flammability

Question 12

How does viscosity change as hydrocarbons change

Answer 12

As chain length increases, viscosity increases

Question 13

How does boiling point change as hydrocarbons change

Answer 13

As chain length increases, boiling point increases

Question 14

How does flammability change as hydrocarbons change

Answer 14

As chain length increases, flammability decreases

Question 15

Example of how properties of hydrocarbon affects fuel usage

Answer 15

Short chain hydrocarbons with lower boiling points used as bottled gases - stored under pressure as liquids in bottles

Question 16

When does complete combustion occur

Answer 16

When there’s plenty of oxygen

Question 17

What happens in complete combustion

Answer 17

• carbon + hydrogen in fuels are oxidised
• carbon dioxide + water produced
• energy released

Question 18

Complete combustion word equation

Answer 18

hydrocarbon + oxygen –> carbon dioxide + water

Question 19

What are hydrocarbons used for

Answer 19

Fuels

Question 20

Why are hydrocarbons used for fuels

Answer 20

Release much energy during complete combustion

Question 21

What kind of fuel is crude oil

Answer 21

Fossil fuel

Question 22

How is crude oil formed

Answer 22

• biomass (mainly plankton) dies, falls to bottom of ocean
• become buried in mud
• remains turn into crude oil over millions of years due to high temperatures from Earth’s magma
• drilled up from rocks

Question 23

Problem with crude oil

Answer 23

• finite
• being used up faster than its being formed
• so will run out one day

Question 24

What is crude oil made up of

Answer 24

Very large number of different compounds, mostly alkane hydrocarbons

Question 25

How is crude oil separated

Answer 25

Fractional distillation

Question 26

How is crude oil separated through fractional distillation

Answer 26

- oil heated until most evaporates - gases enter fractionating column, liquid drains out - column has temperature gradient - hot at bottom, gets cooler upwards - so longer hydrocarbons (with high BPs) condense back into liquids + drain out column early on (at bottom) - shorter hydrocarbons (with low BPs) condense back into liquids + drain out later on (near top) - result - crude oil separated into fractions, each fraction has mixture of hydrocarbons with similar number of carbon atoms so similar BPs

Question 27

Uses of crude oil

Answer 27

- transport - petrochemical industry

Question 28

How is crude oil used in transport

Answer 28

- cars, trains, planes - petrol, diesel oil, kerosene, LPG, heavy fuel oil

Question 29

How is crude oil used in petrochemical industry

Answer 29

- uses hydrocarbons from crude oil as feedstock to make new compounds - compounds used in things like polymers, solvents, lubricants, detergents

Question 30

Why is there a vast array of natural and synthetic carbon compounds

Answer 30

Carbon atoms have ability to form families of similar compounds

Question 31

Demand of short-chain hydrocarbons

Answer 31

High

Question 32

Demand of long-chain hydrocarbons

Answer 32

Low

Question 33

Why is demand of short-chain hydrocarbons high

Answer 33

Make good fuels

Question 34

Why is demand of long-chain hydrocarbons low

Answer 34

Form thick gloopy liquids like tar, less useful

Question 35

Cracking

Answer 35

Splitting up long-chain hydrocarbons into (more useful) shorter-chain hydrocarbons by forming an alkane + alkene

Question 36

Most reactive - alkanes or alkenes

Answer 36

Alkenes

Question 37

Uses of alkenes

Answer 37

- used as starting materials when making other compounds - can be used to make polymers

Question 38

How to test for presence of alkenes

Answer 38

- orange bromine water added to alkane in test tube - shake - solution goes colourless - bromine reacted with alkene to make colourless compound - solution remains orange - no reaction, no alkene

Question 39

What type of reaction is cracking

Answer 39

Thermal decomposition

Question 40

Thermal decomposition

Answer 40

Breaking molecules down by heating them

Question 41

Types of cracking

Answer 41

- catalytic - steam

Question 42

Catalytic cracking

Answer 42

- heat long-chain hydrocarbons to vaporise - pass vapor over hot powdered aluminum oxide catalyst - long-chain molecules split apart on surface of specks of catalyst

Question 43

Steam cracking

Answer 43

- vaporise long-chain hydrocarbons - mix them with steam - heat at high temperature

Question 44

How to draw an alkene

Answer 44

- x1 C=C - 2 hydrogens bonded to it - make sure every carbon atom has **4 bonds**

Question 45

Example of how cracking is useful

Answer 45

- **decane** is in crude oil - cracked into **octane + ethene** - octane - useful for petrol - ethene - useful for making plastics