Unit 2: Alkenes and Alcohols

Question 0

Describe the C=C double bond

Answer 0

Made up of a sigma and pi bond

• sigma bond is formed between two Carbon atoms by the overlap of the orbitals.
• pi bond is formed above and below the plane of the carbon atoms by sideways overlap of p-orbitals

Question 1

Alkenes and cycloalkenes are what kind of hydrocarbon?

Answer 1

Unsaturated hydrocarbon.

Question 2

Why can’t the double bond rotate?

Answer 2

The pi bond fixes the carbon atoms in position at either end of the double bond, preventing any rotation.

Question 3

What is the shape of an alkene molecule?

Answer 3

Trigonal planar shape with 120 bond angle because there are three regions of electron density surrounding each carbon atom in the double bond

Question 4

Conditions of addition of hydrogen and what does it form?

Answer 4

Nickel catalyst and 150

Alkanes

Question 5

Conditions of addition of halogens and what does it form?

Answer 5

No particular conditions, forms dihalogenoalkanes

Question 6

How do you test for the presence of a double bond?

Answer 6

Bromine water test:
Add bromine
Colour changes from orange to colourless if double bond is present

Question 7

Conditions for addition of steam and result

Answer 7

High temperature and pressure
Phosphoric acid catalyst
Ethanol is made
Can be called hydration of ethene

Question 8

Definition of an electrophile

Answer 8

An electron pair acceptor

Question 9

How is margarine manufactured?

Answer 9

Hydrogenation-the oil must be hardened

1. Hydrogen molecules are added across double bonds in an addition reaction.
2. Hydrogenation alters individual molecule in oil so it partially solidifies and hardens

Question 10

What is margarine made from?

Answer 10

Usually vegetable oil

Question 11

Hat is the catalyst used in the manufacture of margarine?

Answer 11

Nickel

Question 12

What two industrial processes is addition polymerisation carries out in?

Answer 12

Ziegler-Natta Process

Radical Polymerisation

Question 13

What conditions does radical polymerisation need?

Answer 13

Very high pressures and 200 Celsius

Question 14

What conditions does the Ziegler-Natta process need?

Answer 14

TiCl3 catalyst and 60 Celsius

Question 15

How are polymers processed into waste?

Answer 15

Recycling
Combustion
Used as a feedstock for cracking

Question 16

Outline the process of separating and recycling polymers

Answer 16

The polymers are sorted based on a polymer identification code, optical scanning and other technical advances are used.
Then processed, mechanically chopping into flakes then washing (to remove impurities)
Sent away to be turned into new materials (by melting and remoulding them)

Question 17

Outline the process of combusting polymers for energy

Answer 17

Burning polymers produces heat energy, which can be used to make electricity.

Question 18

Outline the process if using polymers as a feedstock for cracking

Answer 18

Polymers are being converted into synthesis gas, a mixture of hydrogen and Carbon monoxide. Hydrocarbons and synthesis gas can be used as a chemical feedstock for conversion into useful products.

Question 19

What is the strongest type of intermolecular forces?

Answer 19

Hydrogen bonds

Question 20

What do alcohols have relatively high melting and boiling points?

Answer 20

Because they have hydrogen bonds between the alcohol molecules.

Question 21

Why do alcohols have a lower volatility than alkanes of similar molecular mass?

Answer 21

Because of their hydrogen bonds

Question 22

Definition of volatility

Answer 22

The ease that a liquid turns into a gas. Volatility increases as boiling point decreases.

Question 23

Why do alcohols dissolve in water?

Answer 23

Their hydrogen bonds form between polar -O-H groups if the alcohol and water molecules.

Question 24

Does solubility decrease as the chain length of the alcohol increases or decreases?

Answer 24

Increases

Question 25

Describe the industrial production of ethanol by hydration of ethene

Answer 25

Ethanol is manufactured by the catalytic hydration of ethene. Using:
Steam
And phosphoric acid catalyst
At high temperatures and a moderate pressure
This is a REVERSIBLE REACTION!!!

Question 26

What percentage of ethene is converted into ethanol each time the reagents pass through the reactor?

Answer 26

5%

Question 27

Describe the industrial production of ethanol by fermentation from sugars

Answer 27

Carbohydrates are converted into ethanol and carbon dioxide.
Relatively low temperatures
In presence of yeast
Catalysed by enzyme zymase
Between 25 and 37 degrees because below 25 is too slow and above 37 denatures enzyme.

Question 28

What are the uses of ethanol?

Answer 28

Alcoholic drinks 
A solvent (methylated spirits)

Question 29

What is the use of methanol?

Answer 29

A petrol additive to improve combustion

Question 30

What are the differences between primary, secondary and tertiary alcohols?

Answer 30

The number of alkyl groups attached to the carbon carrying the alcohol group. 
H-O-C-C-H and H-O-C-H are primary
C-C-C
     |
     OH is secondary 
     C
     |
C-C-C
     |
     OH is tertiary