Fuels

Question 1

What is Organic Chemistry

Answer 1

The study of the compounds of Carbon

Question 2

What is a Hydrocarbon

Answer 2

A compound that contains only hydrogen and carbon

Question 3

What are fossil fuels and name a fossil fuel that contributes to the ‘greenhouse effect’

Answer 3

Fuels that were formed from the remains of plants and animals that lived millions of years ago.
Methane if formed from the materials of plant and animal origin.

Question 4

Define saturated compound

Answer 4

One in which there are only single bonds between the atoms in the molecule

Question 5

Define unsaturated compound

Answer 5

One that contains one of more double or triple bonds between the atoms in a molecule

Question 6

What is a homogenous series.

Answer 6

A series of compounds of similar chemical properties, showing graduation in physical properties, having a general formula for its members, each member having a similar method of preparation, each member differing from the previous member by a (CH2) unit

Question 7

What are structural isomers

Answer 7

compounds that have the same molecular formula but different structural formulas.

Question 8

In the preparation of ethene the reaction can be called two things, name both.

Answer 8

Dehydration reaction

Elimination reaction

Question 9

Name a safety precaution in the preparation of ethene

Answer 9

Suck-Back

Question 10

Name any one test for unsaturation

Answer 10

Add bromine to a test tube of Ethene, shake and the colour change is Red to colourless.
Add dilute acidified Potassium Permanganate to a test tube of ethene, shake and the colour change is purple to colourless.

Question 11

Name the physical properties of ethene

Answer 11

It is a colourless gas with a sweetish smell. It is insoluble in water but does dissolve in organic solvents.

Question 12

Describe the heat of combustion of ethene.

Answer 12

a lighted wax taper is applied to the mouth of a test tube containing ethene. When the gas has stopped burning, some limewater is added to test for carbon dioxide (will turn milky). The gas burns with a yellow luminous flame.
C2H4 + 3O2 –> 2CO2 + 2H20

Question 13

Name any one use of Ethene.

Answer 13

Ripens fruit and flowers, manufacture polyethene

Question 14

What substance is used in the preparation of ethyne. Describe it

Answer 14

calcium carbide (CaC2)
grey-black solid

Question 15

In the preparation of ethyne, impurities can be present in the gas, name two impurities and how to remove them

Answer 15

Calcium sulfide (CaS), Calcium phosphide (Ca3P2), calcium nitride (Ca3N2)
Remove by bubbling the gas through acidified copper (II) sulfate solution

Question 16

Name the physical properties of ethyne.

Answer 16

It is a colourless gas with a sweetish smell. It is insoluble in water but soluble in organic solvents.

Question 17

Describe the heat of combustion of ethyne.

Answer 17

a lighted wax taper is applied to the mouth of a test tube containing ethene. The gas burns with a yellow, more luminous flame and a great deal of soot it formed.
2C2H2 + 5O2 –> 4CO2 + 2H20

Question 18

Define aliphatic compounds

Answer 18

An aliphatic compound is an organic compound that consists of open chains of carbon atoms and closed chain compounds that resemble them in chemical properties.

Question 19

Define aromatic compounds

Answer 19

An aromatic compound is a compound that contains the benzene rung structure in their molecules.

Question 20

Discuss the two abnormalities of benzene

Answer 20

1. Benzene was found to be a very unreactive compound eg it did not decolorise bromine water or acidified potassium permanganate, as ethene does. The delocalisation of electrons gives the benzene molecule extra stability and accounts for its unreactivity with regard to addition reactions.
2. The bond lengths in benzene are intermediate between that of a single bond and a double bond.
   - THe c-h bonds are all identical single covalent bonds containing a shared pair of electrons. These bonds may also be described as sigma bonds formed by head-on overlap of singly-occupied atomic orbitals.

Question 21

Explain how a fractionating column works.

Answer 21

The fractionating column separates crude oil into other fuels according to their boiling points.

Question 22

Name any fraction from the fractionating column, their carbon chain lengths, boiling points and use.

Answer 22

Refinery gas/Petroleum gas, 25°C, C1-C4, used as LPGs in gas barbecues.
Petrol/Light gasoline, 50°C,C5-C10, used as fuel for cars.
Naphtha, 100°C,C7-C10, source of useful chemicals eg plastics/medicines.
Kerosene/Paraffin oil, 200°C, C10-C14, use for domestic heating oil.
Diesel oil/gas oil, 300°C, C14-C19, use as fuel for trucks., buses, cars etc.
Lubricating oil, 400°C, C19-C35, used as a lubricant to reduce the wear and tear in engines.
Fuel oil, 400°C, C30-C40, used as a fuel for ships, power stations and heating plants.
Residue oil, <500°C,

Question 23

Define Auto-ignition.

Answer 23

It is the premature ignition or the petrol-air mixture before normal ignition of the mixture by a spark takes place.

Question 24

Define the octane number

Answer 24

The octane number of a fuel is a measure of the tendency of the fuel to resist knocking/ auto-ignition.

Question 25

Name a fuel with an octane number of 0 and its isomer with an octane number of 100.

Answer 25

Heptane = 0

2,2,4-trimethly pentane//iso-octane

Question 26

Name any two things that effect the octane number of a fuel.

Answer 26

The length of the chain, ie the shorter the higher the octane number.
The degree of branching, ie the more branches the chain has the higher the octane number.
Whether it is straight chained or cyclical, ie cyclic compounds have a higher octane number than straight chained compounds.

Question 27

What was used in the 1920s in order to reduce the amount of knocking in fuels. What was its problem

Answer 27

a lead compound called tetraethyl lead was added, Pb(C2H5)4.

These compounds were poisonous to the human health and acted as a poison to the catalytic convertor of the. car.

Question 28

Name and explain three ways to increase the octane number of a fuel.

Answer 28

Isomerisation - changing straight-chain alkanes into their isomers. The alkanes are heated in the presence of a suitable catalyst and this causes the chains to break. When they join again, the final product is more likely to be a branched-chain alkane than a straight-chain alkane.

Catalytic-cracking - the breaking down of long-chain hydrocarbon molecules by the action of heat and catalysts into short chain molecules for which there is a greater demand.

Dehydrocyclisation - involves the use of catalysts to form ring compounds and the removal of hydrogen.

Adding Oxygenates - adding methanol, ethanol or MTBE (methyltertiary- butyl ether) to increase the octane number of a fuel.

Question 29

Name three ways in which hydrogen can be produced, with equations. And a use of hydrogen.

Answer 29

-Steam reformation of natural gas, ie reacting methane
with steam in the presence of a suitable catalyst.
CH4 + H20 –> 3H2 + CO
-electrolysis of water, although it can be expensive
H20 –> H2 + ½ O2
-dehydrocyclisation of alkanes.
use: manufacture of ammonia, as a fuel and organic synthesis.

Question 30

Define the heat of reaction

Answer 30

The heat change when the number of moles of reactants indicated in a balanced equation for the reaction react completely.

Question 31

Define the heat of combustion.

Answer 31

The heat change when one mole of a substance in burned completely in excess oxygen

Question 32

Name the instrument used to calculate the heat of combustion

Answer 32

A bomb calorimeter

Question 33

What is the kilogram calorific value.

Answer 33

It is the heat energy produced when 1 kg of the fuel is completely burned in oxygen.

Question 34

What is the bond energy.

Answer 34

It is the average energy required to break one mole of a particular covalent bond and to separate the neutral atoms completely from each other.

Question 35

Define the heat of neutralisation

Answer 35

The heat change when one mole of H+ ions from an acid react with one mole of OH- ions from a base.

Question 36

Name the acid and the base used in the reaction to determine the heat of neutralisation.

Answer 36

Acid- Hydrochloric acid

Base- Sodium hydroxide

Question 37

Define the heat of formation.

Answer 37

The heat change that takes place when one mole of a compound in its standard state if formed from its elements in their standard states.

Question 38

State Hess’ Law.

Answer 38

If a chemical reaction takes place in a number of stages, the sum of the heat changes in the separate stages is equal to the heat change if the reaction is carried out in one stage.

Question 39

What is the Law of Conservation of Energy

Answer 39

It states that energy cannot be created or destroyed but can only be converted from one form of energy into another.