Organic Chemistry

Question 1

What is a hydrocarbon compound

Answer 1

A compound consisting if hydrogen and carbon only

Question 2

What does the term fraction mean

Answer 2

A fraction is each liquid collected after a mixture is put through the process of fractional distillation

Question 3

As the length of a hydrocarbon increases and it’s physical properties (boiling point, viscosity, flammability)

Answer 3

Longer chain:

Higher boiling point
Viscosity increases
Less volatile (how easily it changes into a gas)

Question 4

Why are short chain hydrocarbons more expensive than long chain ones

Answer 4

They are more useful as the are more flammable

They are harder to store

Question 5

Describe the process of industrial fractional distillation

Answer 5

Crude oil is heated outside the fractionating column and enters as a vapour

Each fraction leaves the fractionating column when it reaches the temperature at which it condenses (it’s boiling point)

Each fraction goes on to be used in different ways

There are holes in the panels separating the fractions to allow lower boiling point fractions to continue to rise

The temperature decreases as you move up the column

Question 6

Give the order of condensation of each fraction and the temperature at which condenses

Answer 6

Bitumen 350

Fuel oil 250-350

Diesel/gas oil 220-250

Kerosene 150-240

Naphtha 75-150

Gasoline 40-75

Refinery/petroleum gas

Question 7

Name the number of carbons and the use as fuels of the different fractions:

Bitumen 
Fuel oil 
Diesel/gas oil 
Kerosene 
Naphtha 
Gasoline 
Refinery/petroleum gas

Answer 7

Bitumen: >70 carbons, road making
Fuel oil: 20-70, oil powered central heating systems
Diesel/gas oil: 15-25, cars lorries buses
Kerosene:9-16, jet aircraft fuel
Gasoline: 4-12, petrol for motor vehicles
Refinery/petroleum gas: 1-4 carbons, bottled gas eg camping gas

Question 8

As the number of carbon atoms in the molecules increases what happens to the boiling point, the volatility, the viscosity and the flammability

Answer 8

Boiling point: increases because more energy is needed to break the intermolecular forces

Volatility: decreases, larger molecules evaporate more slowly because of the strong intermolecular attractions

Viscosity:increases, they flow less easily due to greater intermolecular attractions

Flammability:bigger hydrocarbons burn less easily

Question 9

What is crude oil

Answer 9

Crude oil is a mixture of hydrocarbon compounds

Question 10

What is the general formula for alkanes

Answer 10

CnH2n+2

Question 11

What is the molecular formula for methane

Answer 11

CH4

Question 12

What is the order for the molecular formula from methane to hexane

Answer 12

Methane
Ethane
Propane
Butane
Pentane
Hextane

Question 13

What do alkanes form

Answer 13

A homogulous series of hydrocarbons

Question 14

What do compounds in a homogulous series share

Answer 14

Have a similar chemical formula (chemical reactions)

Show a trend in physical properties(boiling&melting point, viscosity)

Question 15

Can alkane molecules be easily separated

Answer 15

Yes as despite having strong covalent bonds within each molecule, the molecules are attracted by intermolecular forces with are much weaker than covalent bonds and can be easily overcome

Question 16

What happens to the boiling point as the carbon chain length increases

Answer 16

The boiling point increases as there are stinger intermolecular forces between the molecules as there are more points of contact

Question 17

What happens to the viscosity and volatility of a carbon chain as the number of carbons increases

Answer 17

Long chain alkanes are more viscous and less volatile as the chains are longer so it is harder for the molecules to move over eachother and flow. If they are longer they have stinger intermolecular forces and are less volatile

Question 18

What are isomers

Answer 18

Isomers have the same molecular formula but different structural and display formula

Question 19

Is the boiling point of a branched isomer higher or lower than a straight one

Answer 19

Lower as if they were straight they have greater areas of contact between chains leading to stronger intermolecular forces, hence more kinetic energy is needed to overcome these forces

Question 20

What are the options for C5H12 other than pentane

Answer 20

Methyl butane: CH3CH(CH3)CH2CH3

Dimethyl propane: CH3C(CH3)2CH3

Question 21

What happens when an alkane is combusted

Answer 21

It forms water and carbon dioxide/carbon monoxide

Question 22

What does the word saturated mean in terms of organic chemistry

Answer 22

All the carbon atoms are joined by single bonds