3.3.2 Alkanes knowledge

Question 1

what is an alkane?

Answer 1

saturated hydrocarbon that contains only C-H and C-C single bonds

Question 2

what does saturated mean?

Answer 2

compound contains single bonds only

Question 3

what is a hydrocarbon?

Answer 3

compound contains carbon and hydrogen only

Question 4

what is surface contact?

Answer 4

the extent to which 2 molecules are touching one another

Question 5

what is crude oil?

Answer 5

a fossil fuel (non-renewable resource); mixture of hydrocarbons with different chain lengths

Question 6

what is a fraction?

Answer 6

a mixture of molecules with a similar size/boiling point

Question 7

what is a zeolite?

Answer 7

catalyst for catalytic cracking; complex aluminosilicates, and are large lattices of aluminium, silicon and oxygen atoms carrying a negative charge.

Question 8

what is a fuel?

Answer 8

something that can be used to produce useful energy

Question 9

why do Different alkanes have different boiling points?

Answer 9

the boiling point is determined by the carbon-chain length and the number of branches (side-chains)

Question 10

how does C-chain length impact the boiling point of an alkane?

Answer 10

• The boiling point of alkanes increases with increasing C chain length
• alkanes have induced dipole-dipole intermolecular forces
• the strength of these attractions increases with carbon chain length
• as a larger molecule will have more electrons and more electrons means a greater intermolecular force

Question 11

how does the number of branches impact the boiling point of an alkane?

Answer 11

• The boiling point of alkanes decreases with increasing number of branches
• increased number of branches means the molecules have less surface contact so the induced dipole-dipole intermolecular forces are weaker

Question 12

what is the main source of hydrocarbons?

Answer 12

crude oil

Question 13

what is fractional distillation of crude oil used for?

Answer 13

to separate hydrocarbons based on their differing boiling points, as different hydrocarbons have different uses.

Question 14

what is the process of fractional distillation of crude oil?

Answer 14

• fractionating column is cooler at top than bottom
• larger molecules have higher boiling points as they have larger i.d.d
• larger molecules therefore condense at the bottom of the column
• small molecules condense at the top

Question 15

what is cracking used for?

Answer 15

• can be used after fractional distillation to further refine crude oil
• breaks larger fractions (for which supply exceeds demand) into smaller fractions (for which demand exceeds supply); the purpose of cracking is to make alkenes/shorter chain molecules

Question 16

how does cracking make shorter chain molecules?

Answer 16

Cracking involves breaking C-C bond in long alkanes to make shorter alkanes

Question 17

what are the 2 types of cracking?

Answer 17

thermal and catalytic

Question 18

what are the coniditons needed for thermal cracking?

Answer 18

Uses high temperature and pressure

Question 19

what is the temperature range used for thermal cracking?

Answer 19

700-1200K

Question 20

what is the pressure used for thermal cracking?

Answer 20

7000kPa

Question 21

what does thermal cracking produce?

Answer 21

Thermal cracking always produces one alkane, with all other molecules being alkenes

Question 22

what are the conditions needed for catalytic cracking?

Answer 22

Uses high temperature (lower than thermal), slight pressure, and catalyst

Question 23

what is the temperature used for catalytic cracking?

Answer 23

720K

Question 24

what is the pressure used for catalytic cracking?

Answer 24

100kPa

Question 25

what is the catalyst used for catalytic cracking?

Answer 25

zeolite

Question 26

what does catalytic cracking produce?

Answer 26

Catalytic cracking produces a high percentage of branched alkanes and cycloalkanes

Question 27

what are cycloalkanes used for?

Answer 27

cycloalkanes are widely used in motor fuels

Question 28

when does complete combustion occur?

Answer 28

in a plentiful supply of oxygen

Question 29

when does incomplete combustion occur?

Answer 29

in a limited supply of oxygen

Question 30

what do alkanes undergo complete combustion to form?

Answer 30

CO2 and H2O

Question 31

what do alkanes undergo incomplete combustion to form?

Answer 31

CO(g) or C(s), and H2O

Question 32

why is production of CO dangerous?

Answer 32

it is highly poisonous

Question 33

what makes CO poisonous?

Answer 33

it prevents haemoglobin in red blood cells from binding with oxygen

Question 34

what polluting chemicals are produced by the combustion of alkanes?

Answer 34

- CO2 is a greenhouse gas - H2O is a greenhouse gas - CO is a poisonous gas - Solid C damages the lungs

Question 35

how is sulfur dioxide produced in the combustion of alkanes?

Answer 35

Most crude oil deposits contain sulfur as an impurity, so some sulfur is present in most hydrocarbon fuels; when the fuel is burned, the sulphur also burns, producing sulphur dioxide

Question 36

give the equation for the formation of sulfur dioxide?

Answer 36

S(s) + O2(g) ⇒ SO2(g)

Question 37

why is sulfur dioxide dangerous?

Answer 37

Sulphur dioxide gas dissolves in rainwater, forming a very acidic solution of sulphuric acid - acid rain

Question 38

give the equation for the formation of acid rain from sulfur dioxide

Answer 38

SO2 + 0.5O2 + H2O ⇒ H2SO4

Question 39

why is acid rain dangerous?

Answer 39

Acid rain erodes buildings and statues, kills plants, trees, and fish

Question 40

how are nitrogen oxides produced?

Answer 40

At high temperatures, like in car engines, some of the nitrogen in the air reacts with oxygen to produce nitric oxide, nitrogen dioxide, and dinitrogen tetroxide

Question 41

give the equation for the production of nitric oxide

Answer 41

N2(g) + O2(g) ⇒ 2NO(g)

Question 42

give the equation for the production of nitrogen dioxide

Answer 42

NO(g) + 0.5O2(g) ⇒ NO2(g)

Question 43

why are nitrogen oxides dangerous

Answer 43

Nitrogen dioxide dissolves in rainwater, to form an acidic solution of nitric acid - acid rain

Question 44

give the equation for the formation of acid rain from nitrogen dioxide

Answer 44

4NO2 + 2H2O + O2 ⇒ 4HNO3

Question 45

how are unburnt hydrocarbons produced as pollutants?

Answer 45

some of the hydrocarbon fuel is vaporised in the engine, but escapes before it is burned

Question 46

why are unburnt hydorcarbons dangerous

Answer 46

Unburnt hydrocarbons are toxic and can cause cancer is breathed in - contributes towards formation of smog

Question 47

what are 2 Methods to reduce pollution

Answer 47

- Flue Gas Desulphurisation - Catalytic Converters

Question 48

how does flue gas desulpharisation work?

Answer 48

- Any gases produced by power stations are called flue gases - In desulphurisation, the acidic sulfur dioxide gas is neutralised by an alkali

Question 49

what are 2 compounds used in flue gas desulpharisation?

Answer 49

calcium oxide and calcium carbonate

Question 50

how is calcium oxide used in flue gas desulphurisation

Answer 50

A mixture of calcium oxide and water is sprayed into the flue gas which reacts to make solid calcium sulphate.

Question 51

give the equation for the use of calcium oxide in flue gas desulphurisation

Answer 51

CaO(s) + 2H2O(l) + SO2(g) + 0.5O2 ⇒ CaSO4.2H2O(s)

Question 52

how is calcium carbonate used in flue gas desulphurisation

Answer 52

The flue gas is passed through calcium carbonate, which produces solid calcium sulphate.

Question 53

give the equation for the use of calcium carbonaye in flue gas desulphurisation

Answer 53

CaCO3(s) + 0.5O2 + SO2 ⇒ CaSO4 + CO2

Question 54

how can the byproduct of flue gas desulphurisation be used

Answer 54

Solid calcium sulphate can be sold to make builders' plaster

Question 55

how do catalytic converters work

Answer 55

Catalytic converters are designed to convert some of the more harmful gases present in car exhausts into less harmful ones

Question 56

describe the structure of a catalytic converter

Answer 56

- It has a honeycomb structure made of platinum and rhodium

Question 57

why does a catalytic converter have a honeycomb structure

Answer 57

- the honeycomb structure increases the effective surface area, increasing the reaction rate

Question 58

what are 3 compounds removed by catalytic converters

Answer 58

nitrogen monoxide, carbon monoxide, unburnt hydrocarbons

Question 59

give an equation for the removal of carbon monoxide using a catalytic converter

Answer 59

2CO + 2NO ⇒ N2 + 2CO2

Question 60

give an equation for the removal of a hydrocarbon using a catalytic converter

Answer 60

C8H18 + 25NO ⇒ 8CO2 + 9H2O + 12.5N2

Question 61

what is a vacuume distillation unit used for?

Answer 61

- allows heavier fractions to be further separated without high temperatures which could break them down - lowering the pressure over a liquid will lower its boiling point

Question 62

what are some economic reasons for cracking?

Answer 62

- the petroleum fractions with shorter C chains (petrol, naptha) are in more demand than larger - to make use of excess larger hydrocarbons and supply demand for shorter ones, longer ones are cracked - the products of cracking are more valuable than the starting materials (ethene used to make poly(ethene), branched alkanes for motor fuels)

Question 63

why are branched and cyclic hydrocarbons used for making motor fuels?

Answer 63

they burn more cleanly and so give fuels a higher octane number

Question 64

how does complete vs incomplete combustion affect energy production?

Answer 64

incomplete combustion produces less energy per mole than complete

Question 65

what does soot contribute to?

Answer 65

global dimming

Question 66

how does the greenhouse effect work?

Answer 66

- UV wavelength radiation passes through the atmosphere to Earth's surface - the earth radiates out infrared long wavelength radiation - the C=O bonds in CO2 absorb infrared radiation so it does not escape from the atmosphere - this energy is transferred to other molecules in the atmosphere by collisions so the atmosphere is warmed

Question 67

why don't alkanes react with many reagents?

Answer 67

the C-C bond and C-H bond are relatively strong