4.2

Question 1

What are the intermolecular forces in alcohols?

Answer 1

Hydrogen bonding.

Question 2

Are alcohols soluble in water?

Answer 2

Short chain alcohols are likely to be soluble because of the polar OH bond.
Long chain alcohols are less likely to be soluble in water due to prevalence of nonpolar CH bonds.

Question 3

Why do alcohols have greater boiling points compared with alkanes?

Answer 3

Because more energy is needed to overcome the forces of attraction from the hydrogen bonding.

Question 4

How are alcohols classified?

Answer 4

Based on the number of alkyl groups attached to the C-OH.
Primary have 1. Secondary have 2. Tertiary have 3.

Question 5

What are the conditions and products of complete and incomplete combustion?

Answer 5

Complete combustion with sufficient oxygen has products of carbon dioxide and water.
Incomplete combustion with insufficient oxygen has products of carbon, carbon monoxide, carbon dioxide and water. (unburnt hydrocarbons)

Question 6

What happens when primary alcohols are oxidised?

Answer 6

Primary alcohols can be oxidised using acidified (potassium or sodium) dichromate (representing by [O] in equations) to produce either:
-an aldehyde if the reaction is carried out under distillation conditions (where the condenser is on it’s side, so the aldehyde distilled immediately and cannot react any further). Primary alcohol + [O] —> aldehyde + H2O
-a carboxylic acid if the reaction is carried out under reflux (where the condenser is upright, so the aldehyde recondenses back into the flask and reacts again). Primary alcohol + 2[O] —> carboxylic acid + H2O

Question 7

What happens when secondary alcohols are oxidised?

Answer 7

Secondary alcohols can be oxidised to produce ketones, doing so under reflux conditions ensures the reaction is complete. Secondary alcohol + [O] —> ketone + H2O

Question 8

What happens when tertiary alcohols are oxidised?

Answer 8

Tertiary alcohols are resistant to oxidation and therefore no reaction takes place with acidified potassium dichromate.

Question 9

What happens to the oxidation agent when alcohols are oxidised?

Answer 9

It is reduced. In the case of the acidified potassium dichromate (c.H2SO4 + K2Cr2O7) a colour change from orange to green is seen due to the oxidation state of chromium changing from +6 to +3.

Question 10

What is the mechanism for the dehydration of alcohols? Mechanism not required.

Answer 10

Conditions: c.H2SO4 and heat at reflux for 40 minutes.
Equation: e.g. CH3CH2OH —H2SO4/170°C—> H2C=CH2 + H2O
Mechanism: elimination, pair of outer shell electrons on the O -curly arrow-> H+ from catalyst —> C-O bond -curly arrow-> to the O+ —> C-H bond -curly arrow-> C-C bond —> ethene + H2O + H+

Question 11

What is the mechanism for the substitution of alcohols to give haloalkanes? Mechanism not required

Answer 11

Conditions: NaCl + c.H2SO4, NaBr + c.H2SO4, NaI + H3PO4
Equation: ROH + HX -> RX + H2O
Mechanism: nucleophilic substitution, lone pair of :O: -curly arrow-> H+ —> :Br- -curly arrow-> C, C-O+ bond -curly arrow-> O+ —> RX + H2O

Question 12

What is the mechanism for the esterification of alcohols?

Answer 12

Conditions: c.H2SO4, heat
Equation: RCOOH <—> RCOOR’ + H2O
Possible reaction mechanism:

Question 13

What are halogenoalkanes?

Answer 13

Compounds where at least one hydrogen bond in an alkane has been substituted by a halogen.
They are named alphabetically if more than one are present.

Question 14

Which bond in a halogenoalkane is polar?

Answer 14

The bond between the halogen and carbon because there will be a large difference in electronegativity.
As the halogen goes down the group they become less electronegative so the bond polarity decreases.

Question 15

Which species do halogenoalkanes attract and why?

Answer 15

Because the carbon atoms are electron-deficient as the halogen is more electronegative than it.
This means, they attract nucleophiles, for nucleophilic substitution with the halide.

Question 16

What is a nucleophile?

Answer 16

An electron pair donor. It will attack a region of low electron density (δ+).
Common ones include :OH-, H2O:, :NH3, NC:-

Question 17

What is the mechanism for nucleophilic substitution in halogenoalkanes?

Answer 17

Method: heat under reflux with aqueous nucleophile ions.
Sn2: C-Cl bond -curly arrow-> Cl, ion:-curly arrow-> C+

Question 18

Method to determine the rate of hydrolysis of halogenoalkanes:

Answer 18

Independent: the halogen.
Dependent: time taken.
Control: alkyl chain, volume used, concentration, temperature of water bath.

-use a measuring cylinder, add 1cm^3 of each haloalkane to different test tubes.
-put them in a water bath set to 50°C.
-half full three separate test tubes with a mixture of ethanol, water, and aqueous silver nitrate and place them in the same bath.
-when all mixtures reach the set temperature add 1 cm^3 of the ethanol, water, and silver nitrate solution.
-using a stopwatch, measure the time taken until the precipitate appears.

Question 19

What causes the different rates of hydrolysis of halogenoalkanes:

Answer 19

Polarity: C-F > C-Cl > C-Br > C-I, more polar bonds are more attractive to nucleophilic attack, but also have the highest bond enthalpies. We can therefore conclude that bond enthalpy is more important than bond polarity as the more polar haloalkanes have slower rates of hydrolysis.

Question 20

What are CFCs?

Answer 20

Non-toxic, inert organic compounds containing chlorine and fluorine. They were used in refrigerants, aerosol, and fire extinguishers.

Question 21

How does the ozone layer protect us?

Answer 21

Absorbs dangerous UV radiation which might otherwise cause genetic damage, cell mutations, skin cancers, and cataracts. And it stabilises temperatures.

Although, it is toxic when breathed in and contributes to photochemical smog.

Question 22

Mechanism of ozone destruction by CFCs and other radicals:

Answer 22

Initiation: homolytic fission due to UV light: C2F2Cl2 -> C2F2Cl• + Cl•
Propagation steps: Cl• + O3 -> ClO + O2, •ClO + O3 -> Cl• + 2O2
Overall: 2O3 -> 3O2

For other radicals, e.g. •ΝΟ:
R• + O3 -> •RO +O2
•RO2 + O -> •RO + O2
Overall: O3 + O -> 2O2

Question 23

Equipment in organic chemistry:

Answer 23

Condenser, heating mantel, pipette etc.
Separating funnel
Anhydrous salt e.g. MgSO4 or CaCl2
Redistillation

Question 24

Mass spectrometry:

Answer 24

The analysis of fragments ions.
The ion peak is the RFM.
A small M+ 1 peak from the small portion of carbon-13.

Question 25

What happens to bonds exposed to infrared radiation?

Answer 25

Covalent bonds vibrate more and absorb energy.
This absorption by atmospheric gases containing C=O, O-H, and C-H bonds causes global warming, with this acceptance of evidence leading to government policies on renewable energy supplies.

Question 26

Uses of infrared spectroscopy:

Answer 26

-monitor gases causing air pollution from car emissions.
-breathalysers to measure ethanol in breath.