3.4 Alcohols and Carboxylic Acids

Question 1

alcohol general formula

Answer 1

Question 2

When naming alcohols, we:

Answer 2

identify the longest chain of carbons

identify if it is an alkane or alkene then drop the last ‘e’ and add the suffix –ol

identify the position of the alcohol group in the chain and place the number before the –ol

Question 3

If the –OH group is not the main functional group in the chain

Answer 3

it is referred to as a ‘hydroxy-’ group and this appears as a prefix in the name, for example:

Question 4

alcohols Physical Properties
Solubility

Answer 4

Alcohols are liquids so we talk about miscibility (how easily a liquid mixes with water). Smaller chain alcohols are miscible in water due to their ability to hydrogen bond with water molecules.

When mixed, the alcohol-alcohol hydrogen bonds, and water-water hydrogen bonds break and new water-alcohol hydrogen bonds form. This is possible as there is no significant difference (gain or loss) in energy when this happens.

Methanol and ethanol are completely miscible in water, but miscibility decreases as the hydrocarbon chain length increases. Hydrogen bonding still occurs between water and the hydroxyl group, but the hydrocarbon chain disrupts bonding between other water molecules. These chains can only interact with the water molecules via Van der Waals forces.

Question 5

Answer 5

Question 5

alcohols Physical Properties

volatility

Answer 5

Question 6

Industrial Production of Ethanol

Answer 6

Industrial ethanol is made by the addition reaction of steam with ethene in the presence of a phosphoric acid, H3PO4, catalyst. It is a continuous process and ethanol with a concentration of up to 96% alcohol by volume can be produced on an extremely large scale.

Question 7

Fermentation - Ethanol

Answer 7

Ethanol is made by the anaerobic fermentation of sugars found in plant-based materials such as wheat and grapes. It is a batch process with anywhere between 2500 dm3 and 210000 dm3 of alcohol being produced at a time depending in the size of the brewery. However, the concentration of alcohol produced may only be around 12% - 15% alcohol by volume.

Question 8

Uses of Alcohols

Answer 8

Question 9

Bioethanol is produced by

Answer 9

the fermentation of sugars in plants and biodiesel is produced from the oils and fats present in the seeds of some plants.

Question 10

Advantages - Biofuels

Answer 10

Question 11

Disadvantages - Biofuels

Answer 11

Question 12

Answer 12

Question 13

The alcohol can be dehydrated to form an alkene when reacted with either:

Answer 13

hot, concentrated sulfuric acid (H2SO4, >150°C)

hot pumice (Al2O3, >300°C)

phosphoric acid (H3PO4, >300°C)

Question 14

With secondary alcohols (containing four or more carbons atoms), dehydration can form two different alkenes:

The C=C bond is formed by an elimination reaction, in this case as water is lost. It can also be called a dehydration reaction.

Answer 14

Question 15

Answer 15

Question 16

Aliphatic alcohols can be oxidised

Answer 16

Question 17

Oxidation of Alcohols
Primary alcohols: Mild oxidation

Answer 17

Question 18

Primary alcohols: Further oxidation

Answer 18

Question 19

Secondary alcohols: Mild oxidation

Answer 19

Question 20

Tertiary alcohols

Answer 20

Tertiary alcohols do not undergo oxidation under these conditions using acidified dichromate(VI).

Question 21

Oxidation Colour Change

Answer 21

During the process of oxidation the orange colour of the dichromate(VI) ion Cr2O72-(aq) changes to the green colour of the chromium(III) ion, Cr3+(aq). This is a reduction. This colour change can therefore be used as a laboratory test for a 1° or 2° alcohol (or aldehyde).

Question 22

🔥 Oxidation of Alcohols using Acidified Dichromate(VI)

Answer 22

Question 23

🧪 Alcohol Types and Oxidation

Answer 23

Question 24

A combination of two chemical tests can be carried out to determine the classification of an unknown alcohol. Firstly carry out an oxidation reaction using acidified aqueous dichromate(VI) under reflux conditions. Secondly test any product with blue litmus paper:

Answer 24

Question 25

Carboxylic acids can be formed by

Answer 25

the oxidation of alcohols using acidified dichromate(VI) H+/Cr2O7

Question 26

Solubility of carboxylic acids

Answer 26

As a result, the group will undergo hydrogen bonding with water molecules. Carboxylic acids with chains of 4 carbons or less are very soluble in water. Chains of five carbons and longer become progressively less soluble. This is due to the fact that the hydrocarbon chain is non-polar and can only undergo Van der Waals interactions so cannot break the hydrogen bonding that exists between water molecules.

Question 27

Carboxylic acids can form dimers:

Answer 27

Question 28

Answer 28

Question 29

Reactions of carboxylic acids

Answer 29

The proton from the carboxyl group can be donated (Brønsted-Lowry acid). This is because the negative charge that results from the loss of a proton can be delocalised over the carbon and oxygen of the carbonyl group. This delocalisation of charge stabilises the carboxylate ion and the following equilibrium occurs. The equilibrium that forms means that complete dissociation does not occur. As a result, they are weaker acids than hydrochloric or sulfuric acid, which dissociate fully. Carboxylic acids will undergo the typical reactions of an acid to form carboxylate salts.

Question 30

carboxylic acids Reactions with metals

Answer 30

A carboxylic acid will react with a metal, forming a salt and hydrogen gas. This will be seen as effervescence in the solution. In the example below the salt formed is called magnesium propanoate and has the formula (CH3CH2COO)2Mg:

Question 31

carboxylic acids Reactions with bases

Answer 31

A carboxylic acid will react with a base, forming a salt and water: Most salt solutions formed in this way will be colourless so no visible change will be seen. In a reaction involving transition metal bases, a coloured solution could be formed, e.g. copper(II) oxide, a blue solution due to the formation of the copper(II)carboxylate salt will be seen.

Question 32

carboxylic acids Reactions with carbonates and hydrogen carbonates

Answer 32

Question 33

Write ionic equations for each of the carboxylic acid reactions above.

Answer 33

Question 34

When a carboxylic acid reacts with an alcohol

Answer 34

in the presence of an acid catalyst (usually conc. sulfuric acid, H2SO4), an ester forms. In the reaction, the OH bond in the alcohol is broken. Conditions: warm the reactants under reflux with an acid catalyst (usually sulfuric acid).

Question 35

🌸 Esterification Reaction (Condensation Reaction)

Answer 35

Question 36

Esterification Reaction ⚖️ Improving Yield Using Le Chatelier’s Principle

Answer 36

Question 37

Naming esters

Answer 37

Question 38

equations for the formation of the ester

Answer 38

Question 39

Separation of the ester

Answer 39