organic chemistry

Question 1

Alkane general formula

Answer 1

CnH2N+2

Question 2

names of alkanes

Answer 2

Methane
Ethane
Propane
Butane
Pentane

Question 3

molecular formula for ethane + definition

Answer 3

C2H6 - actual number of atoms of each element in a compound

Question 4

empirical formula for ethane + definition

Answer 4

CH3 - simplest whole number ratio number of atoms of each element in a compound

Question 5

structural formula for ethane + definition

Answer 5

CH3CH3 - written representation of how the carbon atoms are arranged

Question 6

isomerism definition

Answer 6

molecules with the same formula but different structural formulae

Question 7

what is the homologous series

Answer 7

The homologous series is a group of compounds which have the same general formula e.g. CnH2n+2 for alkanes

Question 8

hydrocarbon definition

Answer 8

atoms that only consist of carbon and hydrogen

Question 9

organic chemistry definition

Answer 9

molecules that contain carbon

Question 10

saturated definition

Answer 10

only consists of single covalent bonds

Question 11

unsaturated definition

Answer 11

contains double or triple bonds between carbon atoms

Question 12

fraction definition

Answer 12

group of molecules with similar boiling points

Question 13

compare long chain hydrocarbons to short chain hydrocarbons (5-6 marker)

Answer 13

• short chain hydrocarbons are more useful than long chain molecules as they ignite more easily so can be used as fuels e.g. petrol
• however there is a much greater supply for then longer hydrocarbons
• to meet the demand for the smaller hydrocarbons, long hydrocarbons are split into smaller molecules by a process called cracking

Question 14

what is crude oil

Answer 14

a mixture of molecules (mainly hydrocarbons)

Question 15

describe the process of fractional distillation (6 marks)

Answer 15

• the process which separates crude oil out
• crude oil is heated up until it vaporizes
• vapors rise up the column until they reach a temperature just below their boiling point where they condense different molecules at different temperatures due to different boiling points
• the column is cooler on the top than the bottom

Question 16

Explain why cracking is necessary, stating the types of molecules produced and the conditions needed for industrial cracking (5 marks)

Answer 16

• Breaks long chain hydrocarbons into short chain hydrocarbons using heat (600-700C) with the presence of a catalyst (alumina or silica)
• Short chain hydrocarbons are in higher demand as they create things such as fuel

Question 17

state the general formula of alkenes

Answer 17

CnH2n

Question 18

name a different product that could be formed if butane undergoes incomplete combustion

Answer 18

carbon monoxide (CO)

Question 19

describe + explain a possible consequence for health of the incomplete combustion of hydrocarbons

Answer 19

lets out greenhouse gases which contributes to global warming

Question 20

describe the link between the size of the molecules in crude oil fractions and their boiling points

Answer 20

higher boiling point larger size molecules

Question 21

describe how the viscosity of the fractions changes from top to bottom of column

Answer 21

greater viscosity as you go down the column

Question 22

explain why yeast is used in a fermentation reaction

Answer 22

contains enzymes which speed up the reaction

Question 23

give 2 uses of alcohol

Answer 23

fuel and alcoholic drinks

Question 24

combustion equation for ethanol

Answer 24

C2H5OH + 3O2 = 2Co2 + 3H2O

Question 25

give 2 ways ethanol can be oxidised

Answer 25

1 - by oxygen and bacteria into ethanoic acid

2 - oxidized to ethanoic acid using potassium dichromate solution with sulfuric acid. If the reaction works the solution changes from orange to green.

Question 26

give two uses of fuel oil

Answer 26

• fuel for large ships
• power stations

Question 27

would you expect heptane (98C boiling point C7H16) or triacontane (450C boiling point C30H62) to be collected further down the fractioning column? Explain your answer, with reference to the boiling points of the hydrocarbons

Answer 27

• Triacontane because the fractioning column is the hottest at the bottom
• so hydrocarbons with higher boiling points will be collected further down the column
• Triacontane has a higher boiling point than heptane because triacontane is a bigger molecule meaning it will be collected lower down

Question 28

fumes from faulty central heating boilers can contain carbon monoxide

what can cause carbon monoxide to be produced when fuel is burnt in a boiler?

Answer 28

• if it’s burnt without enough oxygen

Question 29

describe the effect of Co2 on the human body

Answer 29

it is toxic preventing oxygen being carried in the blood leading to death

Question 30

nitrogen oxides can be produced when fossil fuels are burnt

describe the conditions needed for nitrogen oxides to form and give an example of where this reaction might take place

Answer 30

• high temperatures
• may take place in a car engine

Question 31

nitrogen oxides react with water vapour in the atmosphere. Name the product that is formed when this occurs

Answer 31

• nitric acid

Question 32

nitrogen oxides contribute to acid rain. name one other gas that contributes to acid rain

Answer 32

• sulfur dioxide