organic chem

Organic chemistry

The chemistry of carbon compounds

What is the general formula of a homologous series used for?

To calculate the molecular formula of any member of the series.

What does 'n' represent in the general formula of a homologous series?

The number of carbon atoms.

An example of a general formula

CnH2n + OH

What is the molecular formula?

The molecular formula of a compound shows the number of each type of atom present in one molecule of the compound

An example of the molecular formula

C2H6O

What is the displayed formula?

The displayed formula of a compound shoes the arrangement of atoms in a molecule as well as all the bonds

An example of a displayed formula

H H

O
|
H—C—C—H

What is the homologous series?

A homologous series is a group of molecules with the same functional group but a different number of -CH2 groups

What is the functional group?

A functional group is an atom or group of atoms responsible for the typical chemical reactions of a molecule

What is a saturated alkane?

Saturated - A saturated hydrocarbon contains no carbon-to-carbon double bonds, only single bonds

What is an unsaturated alkene?

Unsaturated - An unsaturated compound contains at least one double or triple bond

What is a hydrocarbon?

A compound that only contains carbon and hydrogen atoms only

What is the smallest alkane?

Methane (CH4) (1 Carbon)

Are alkanes saturated or unsaturated ?

Saturated - each carbon atoms forms four single covalent bonds

Are alkenes saturated or unsaturated ?

Unsaturated - they have a c=c double bond

What is the functional group of an alkene?

C = C (double bond)

What is the general formula of an alkane?

CnH2n+2

What is the general formula of an alkene?

CnH

How many carbons does ethanol have? (Alkane)

2 Carbons, 6 Hydrogens

How many carbons does propane have? (Alkane)

3 Carbons, 8 Hydrogens

How many carbons does butane have? (Alkane)

4 Carbons, 10 Hydrogens

How many carbons does pentane have? (Alkane)

5 Carbons, 12 Hydrogens

How many carbons does hexane have? (Alkane)

6 Carbons, 14 Hydrogens

What is the boiling point in reference to alkanes?

As the length increases the boiling point increases

What is the state of the first four hydrocarbons (Methane, Ethanol, Propane, Butane) at room temperature?

Gases at room temperature

What happens as the hydrocarbons increase their boiling points? (Pentane, Hexane)

They become liquids at room temperature

Shorter alkanes have a low boiling point, what property do they have?

Shorter alkanes are more volatile meaning they evaporate more easily

Longer alkanes have a high boiling point so, what property do they have?

They are more viscous (thick)

Which alkanes are more flammable?

Shorter alkanes

Test for alkenes

Add bromine water to the alkene solution, the solution goes from brown to colourless if alkenes are present

When alkenes are added together what do they make?

Polymers - double bond can break to form two or more bonds = bond to the adjacent molecules

What are the main reasons we use hydrocarbons?

Fuel

When does complete combustion occur?

When there is plenty of oxygen

Complete combustion

hydrocarbon + oxygen --> carbon dioxide + water

What type of reaction is complete combustion?

Exothermic reaction

What is crude oil

A fossil fuel, mixture of lots of hydrocarbons

How is crude oil formed?

Via remains of dead plants and animals (plankton) that died millions of years ago and buried in the mud, the high temperatures in the ground turns this into crude oil = soaked into the rocks and stored fro millions of years

Where do we get crude oil from?

From drilling into rocks and sucking it up to the surface

What kind of resource is crude oil?

Finite resource, will run out (non renewable)

How do we separate the hydrocarbons from the crude oil?

Fractional distillation

What is fractional distillation?

A process of heating something up and separating the hydrocarbons by taking advantage of their different boiling points

What is the process of fractional distillation?

1. Heat the oil in a chamber until its turned into a gas

2. Pass the mixture in a fractioning column

3. The gas (heated up oil) will gradually rise up and once it reaches a point where it is cooler than their boiling point it will condense into a liquid

What is the main property of the fractionating column?

It is hot at the bottom and gradually cooler at the top

What will the hydrocarbons with the most chains do in the fractionating column?

They have the highest boiling point so they will drain out of the column the quickest as it is not hot enough to keep it in its gaseous state

The hydrocarbons that leave the fractionating column the earliest produce what?

Bitumen (tar on the roads) and Heavy Fuel oils (Heating oil, fuel oil, or lubricating oil)

The hydrocarbons that leave the fractionating column the latest produce what?

Diesel, kerosene, petrol

Which fractions makes the best fuels?

Petrol, kerosene, diesel - they're the most flammable

What are petrochemicals?

Products derived from oil and natural gas -> feedstock

What is feedstock used for?

Solvents, polymers, lubricants, detergents

What is cracking?

Thermal decomposition - breaking down of long-chain alkanes into alkenes and shorter-chain alkanes

What types of cracking are there?

Thermal and Catalytic

How to use catalytic cracking?

1. Heat the long term hydrocarbons until it is vaporised (turned into a gas)

2. Pass vapoured hydrocarbons over the catalyst (hot powdered aluminium oxide)

3. As the long hydrocarbons come into contact with the catalyst they will split apart into two smaller hydrocarbons

How to use steam cracking?

1. Heat the long term hydrocarbons until it is vaporised (turned into a gas)

2. Mix them with steam

3. Heat them to a very high temperature = long hydrocarbon chains split apart

Balanced chemical equations for cracking

Long chain alkane --> shorter alkane + alkene