Module 4: Section 2

Question 1

What is the general formula of alcohols?

Answer 1

CnH2n+1OH

Question 2

Why are alcohols soluble in water?

Answer 2

Alcohola are generally polar due to the highlyelectronegative oxygen atom. The hydrogen atom has a slight positive charge which can attract lone pairs on an oxygen from a neighbouring molcule, forming hydrogen bonds.

Question 3

Why does solubility of alcohols decrease as size increases?

Answer 3

As alcohols get bigger, more of the molecule is a non-polar carbon chain.

Question 4

Name the reaction for making a haloalkane from an alcohol.

Give the reagants and conditions.

Answer 4

Substitution reaction.
Requires an acid catalyst (H2SO4)
20 degrees celsius

Question 5

Name the reaction for making an alkene from an alcohol.

Give the reagants and conditions.

Answer 5

Elimination reaction (Water is eliminated to dehydrate the alcohol)
Acid catalyst is required (H2SO4 or H3PO4).
Heat

Question 6

What 2 products are made when you oxidise an alcohol by burning it?

Answer 6

CO2 and H2O

Question 7

What is formed when you oxidise a primary alcohol by:

1. Distillation
2. Reflux

Answer 7

Distill = Aldehyde
Reflux = Carboxylic Acid

Question 8

What is formed when you oxidise a secondary alcohol?

Answer 8

Ketone

Question 9

What is formed when you oxidise a tertiary alcohol?

Answer 9

Nothing. There is no reaction as tertiary alcohols dont react with K2Cr2O7/H+.

Question 10

What colour change occurs when oxidising alcohols?

Answer 10

Orange —-> Green

Except for tertiary alcohols, which stay orange.

Question 11

What reagants are used when oxidising alcohols?

Answer 11

K2Cr2O7 / H2SO4

Question 12

What is a haloalkane?

Answer 12

An alkane with atleast 1 halogen atom in place of a hydrogen atom.

Question 13

Why are haloalkanes more reactive than alkanes?

Answer 13

Halogens are more electronegative than carbon. The carbon-halogen bond is polar and so can be attacked by nucleophiles.

Question 14

Name the reaction to form an alcohol from a haloalkane.

What are the reagants and conditions?

Answer 14

Nucleophilic substitution reaction.
Warm aqueous alkali (NaOH or KOH).
Reflux.

Question 15

In a nucleophilic substitution reaction, name the way the bond breaks

Answer 15

Heterolytically. Both electrons from the C-X bond are taken by the X-

Question 16

When water acts a nucleophile, what is the general equation for the nucleophilic substitution reaction?

Answer 16

R-X + H2O —> R-OH + H+ + X-

Question 17

What does speed of hydrolysis depend on?

Answer 17

Bond enthalpy of the C-X bond.

Question 18

What haloalkanes will hydrolyse the quickest and why?

Answer 18

Iodoalkanes will hydrolyse the fastest as they have the weakest bonds.
C-F is the strongest bond.

Question 19

Give 4 properties of CFC’s

Answer 19

Stable, volatile, non-flammable and non-toxic.

Question 20

What does Ozone in the upper atmosphere do?

Answer 20

It absorbs a lot of UV radiation and re-emits, reducing the amount of UV radiation that reaches the Earths surface.

Question 21

Give 2 alternatives to using CFC’s

Answer 21

HCFC’s (hydrochloroflurocarbons)

HFC’s (hydroflurocarbons)

Question 22

Describe the Greenhouse effect.

Answer 22

Gases in the atmosphere that contain C=O, C-H or O-H bonds are able to absorb IR radiation and re-emit it in all direction, including back down towards earth, keeping us warm.

Question 23

What are the main greenhouse gases?

Answer 23

Water vapour, Carbon dioxide and methane.