Organic Chemistry

Question 1

What is a hydrocarbon?

Answer 1

Any compound that is formed from carbon and hydrogen atoms only!!

Question 2

What are the 2 types of hydrocarbons?

Answer 2

1) Alkanes

2) Alkenes

Question 3

What is the main difference between alkanes and alkenes?

Answer 3

Alkanes only have single C-C bonds, whereas alkenes have 1 or more C=C double bond present within the compound.

Because carbon atoms bond with the maximum number of hydrogen atoms possible, alkanes are regarded as being saturated.

Because carbon atoms have double bonds between each other, the carbon atoms arent able to bond with the maximum number of possible hydrogen atoms. Hence, alkenes are regarded as being unsaturated.

Question 4

What are examples of alkanes?

Answer 4

> Methane (CH4)
Ethane (C2H6)
Propane (C3H8)
Butane (C4H10)

Question 5

What is the equation to work out the chemical formula for each alkane?

Answer 5

CnH2n+2

Question 6

What are examples of alkenes?

Answer 6

> Ethene (C2H4)
Propene (C3H6)
Butene (C4H8)

Question 7

What is the equation to work out the chemical formula for an alkene?

Answer 7

CnH2n

Question 8

What happens to the properties of hydrocarbon as the chain gets longer?

Answer 8

> Melting and boiling point increases because more bonds are needed to be broken with larger chains of hydrocarbon molecules. As a result, shorter chain hydrocarbon molecules are very volatile e.g. methane gas used for cooking.
Viscosity increases with increasing hydrocarbon chain - this is because more bonds are made with larger chains. Therefore shorter chains are very runny.
Shorter chain hydrocarbons are easier to ignite i.e. they are more flammable - we use methane (short hydrocarbon molecule) to heat up our cooking.

Question 9

What is meant by combustion?

Answer 9

The process by which we react hydrocarbons with oxygen to release energy (amongst with other products e.g. carbondioxide, water).

Question 10

What are the two types of combustion?

Answer 10

> Complete combustion ==> reaction of hydrocarbons with PLENTY of oxygen.
Incomplete combustion ==> reaction of hydrocarbons with NOT ENOUGH/ABSENCE of oxygen.

Question 11

What are the products of complete combustion?

Answer 11

> Energy released
Carbon dioxide
Water

Question 12

What is the word equation for complete combustion?

Answer 12

Hydrocarbon + Oxygen ==> Carbondioxide + Water (+ energy released).

Question 13

What is crude oil?

Answer 13

> Crude oil is a fossil fuel made from the remains of plants and animals (mainly plankton) that died millions of years ago and were buried in mud. Over millions of years, with high temperature and pressure, the remains become converted into crude oil. This oil can then be drilled up.

Question 14

What are the different types of fossil fuels?

Answer 14

> Coal
Natural gas
Crude oil

NB: These are examples of non-renewable fuels?

Question 15

What is meant by a non-renewable fuel?

Answer 15

Its a finite resource that takes a long time to generate (making its rate of usage faster than its rate of generation) ==> it will eventually run out!!!

Question 16

What is meant by fractional distillation?

Answer 16

Fractional distillation is the process by which we separate hydrocarbons.

Question 17

Describe the process of fractional distillation?

Answer 17

> Crude oil is a mixture of hydrocarbons.
Cruide oil becomes heated up during fractional distillation.
The chamber is hottest at the bottom and coldest at the top.
Short chain hydrocarbons require a small amount of energy to break their bonds. Therefore, they become separated from the crude oil mixture at the top of the distillation chamber (TOP = COLD).
Long chain hydrocarbons require a greater amount of energy to break their larger number of bonds. Therefore, they only become separated from the crude oil mixture at the bottom of the chamber (where it is hottest).

Fractional distillation therefore allows you to separate crude oil into different sized fractions (of hydrocarbons).

Question 18

What are the uses of crude oil in modern day life?

Answer 18

> Transport e.g. diesel oil, kerosene, liquid petroleum gas.
The petrochemical industry also uses hydrocarbons from the crude oil mixture as feedstock to make new compounds e.g. polymers, solvents, lubricants and detergents.

Question 19

What is meant by cracking?

Answer 19

Cracking is the process by which we split up large hydrocarbon molecules into smaller chain hydrocarbon molecules, along with other molecules for examples alkanes and alkenes.

Question 20

Which type of hydrocarbons are more reactive (alkanes or alkenes)?

Answer 20

Alkenes - this is because we can break the double C=C bond to form other bonds as well.

Question 21

How can we test for alkenes?

Answer 21

We test for the presence of alkenes by the use of bromine water.

When orange coloured bromine water is added to an alkane, no reaction happens and as a result it will stay bright orange.

However, when orange coloured bromine water is added to an alkene, the bromine water reacts with the alkene and as a result, the solution becomes colourless - therefore the bromine water in effect becomes decolourised.

Question 22

What are the different methods to carry out cracking?

Answer 22

1) Catalytic cracking - here specks of catalysts are used

2) Steam cracking - this is where you vaporise the hydrocarbon and mix it with high temperatured (hot) steam.