Alcohols And Haloalkanes

Question 1

Are alcohols polar or non-polar? Why?

Answer 1

Generally polar due to the electronegative hydroxyl group which pulls the electrons in the C-OH bond away from the carbon atom. The -OH group is also polar with a delta negative charge on the oxygen atom and a delta positive charge on the hydrogen atom

Question 2

How does the size of an alcohol affect its solubility? Why?

Answer 2

As alcohols increase in size their solubility in water decreases.
When alcohols are mixed with water, hydrogen bonds are formed between the OH group and H2O.
If it’s a small alcohol hydrogen bonding let’s it mix freely with water.
In larger alcohols, most of the molecule is a non-polar chain, so there is less attraction for the polar H2O molecules.

Question 3

What is the boiling point and volatility of alcohols like?

Answer 3

Relatively low volatility and relatively high BP compared to non-polar compounds of similar sizes because alcohols can form hydrogen bonds with each other &hydrogen bonding is the strongest type of intermolecular force.

Question 4

What does a substitution reaction of an alcohol become? What catalyst is needed?

Answer 4

Alcohols react with compounds containing halide ions in a substitution reaction to become a haloalkane. Requires an acid catalyst such as H2SO4

Question 5

What does an elimination reaction of an alcohol form? What catalyst is required?

Answer 5

Eliminating water from an alcohol forms an alkene. Can form an E/Z isomer as the OH group is removed but also an H, the H will be removed from a carbon adjacent to the carbon with the OH attached. Different isomers can form depending on which H is removed. (Pg248) Acid catalyst needed (concentrated H2SO4 or concentrated H3PO4. The mixture is then heated.

Question 6

What oxidising agent is needed to mildly oxidise an alcohol?

Answer 6

Acidified potassium dichromate(VI). (K2Cr2O7/H2SO4)

Question 7

What are primary alcohols oxidised to? What method is used to get the products?

Answer 7

Aldehydes and the carboxylic acids. Distillation to get aldehyde, reflux to get carboxylic acid

Question 8

What are secondary alcohols oxidised to? What method is used?

Answer 8

Ketones. Using reflux

Question 9

What is the colour change when oxidising an alcohol with acidified potassium dichromate?

Answer 9

Orange dichromate(VI) ion, is reduced to the green chromium(III) ion

Question 10

What is the functional group of an aldehyde and a ketone?

Answer 10

CnH2nO

Question 11

What is the suffix of an aldehyde?

Answer 11

-al (e.g. propanal)

Question 12

What is the suffix for a ketone?

Answer 12

-one (e.g. propanone)

Question 13

What is the difference between an aldehyde and a ketone?

Answer 13

Aldehyde has =O on end of chain, ketone has =O in middle of chain

Question 14

What is a haloalkane?

Answer 14

An alkane with at least 1 halogen atom in place of a hydrogen

Question 15

Are haloalkanes polar?

Answer 15

Yes - halogens generally much more electronegative than carbon, so the carbon-halogen bond is polar

Question 16

What mechanism do haloalkanes react in?

Answer 16

Nucleophilic substitution reactions

Question 17

What are haloalkanes hydrolysed to make? How?

Answer 17

Alcohols:
1. Hydrolysis with aqueous alkali
2. Hydrolysis with water

Question 18

What does the speed of haloalkanes being hydrolysed depend on? How can this be measured?

Answer 18

Bond enthalpy - weaker carbon-halogen bonds break more easily. Iodoalkanes have the weakest bonds so hydrolyse fastest, fluroalkanes have strongest bonds, so are slowest at hydrolysing.
Can be measured by adding silver nitrate solution and timing how quickly a precipitate forms and a cross disappears

Question 19

How can you identify a haloalkane?

Answer 19

React sample with water, silver nitrate solution and ethanol. Colour if precipitate formed tells you which halogen is present. Yellow = iodoalkane, cream = bromoalkane, white = chloroalkane

Question 20

What are features of chlorofluorocarbons?

Answer 20

Very stable, volatile, non-flammable, non toxic

Question 21

What is the issue with CFCs?

Answer 21

Destroys ozone layer. Ozone molecules absorb a lot of ultraviolet radiation which can cause sunburn and skin cancer

Question 22

What is the mechanism for ozone depletion?

Answer 22

CF2Cl2 + UV -> CF2Cl radical + Cl radical
Cl radical + O3 -> O2 + ClO radical
ClO radical + O -> O2 +Cl radical (regeneration of Cl radical)
Overall reaction: O3 + O2 -> 2O2 (Cl radical is catalyst)

Question 23

Other than CFCs what also breaks down ozone?

Answer 23

NO radicals from nitrogen oxides

Question 24

What are alternatives to CFCs

Answer 24

HCFCs & HFCs used for now
HCFCs still damage ozone but much less
HFCs don’t contain Cl so don’t damage ozone
Both HCFCs and HFCs are greenhouse gases
Some hydrocarbons used in fridges, most aerosols use pump spray systems or nitrogen as propellant, industrial fridges & freezers use ammonia

Question 25

What is the greenhouse effect?

Answer 25

The absorption and re-emission of infrared radiation by greenhouse gases in the troposphere

Question 26

What are the main greenhouse gases?

Answer 26

Water vapour, carbon dioxide, methane

Question 27

How do greenhouse gases cause global warming?

Answer 27

The C=O, O-H and C-H bonds in these molecules absorb IR radiation which makes the bonds vibrate more, extra energy is passed on to other molecules in the air by collisions giving other molecules more kinetic energy and raising overall temperature.

Question 28

What does the contribution of a greenhouse gas on the greenhouse effect depend on?

Answer 28

1. How much IR radiation one molecule of the gas absorbs
2. How much of that gas there is in the atmosphere
3. How long the gas stays in the atmosphere for

Question 29

What is global warming?

Answer 29

The warming if the planet due to increased concentrations of greenhouse gases in the troposphere, which enhance the greenhouse effect

Question 30

What are the consequences of global warming?

Answer 30

1. Warmer oceans will expand & ice sheets could melt causing sea levels to rise and more flooding
2. Stormier less predictable weather
3. Less rainfall in some places leading to droughts & crop failures
4. Increased rainfall in some places could bring diseases such as cholera