Chapter 23

Question 1

What are alcohols?

Answer 1

A homologous series of organic compound which have the hydroxyl (-OH) functional group.

Question 2

What are carboxylic acids?

Answer 2

A homologous series of organic acids which have the carboxyl (-COOH) functional group.

Question 3

How is ethanol produced by fermentation?

Answer 3

1. Mix a glucose solution with yeast and keep mixture at 37 degrees celsius
2. During fermentation, carbon dioxide is released. Thus, frothing (formation of foam) can be observed in the flask. A white precipitate is formed in the limewater.
3. A dilute solution of ethanol is produced, up to only about 15% concentration. This is because when the alcohol content exceeds this amount, the yeast dies and fermentation stops. Ethanol can be obtained from this liquid mixture by fractional distillation

Question 4

What are the precautions when setting up the fermentation apparatus for producing ethanol and why?

Answer 4

1. Mixture should be kept at around 37 degrees celsius
   - the enzymes in yeast work best at this temperature. If the temperature is raised beyond 37 degrees celsius, the enzymes will be denatured and hence be unable to catalyse the reaction. Fermentation will stop. Too low a temperature will also render enzymes inactive.
2. Fermentation can only occur in the absence of oxygen. This is done by securing a rubber bung tightly to the flask and having limewater in the test tube to prevent air from entering the apparatus.
   - this is because in the presence of air, bacteria from the air oxidises ethanol to ethanoic acid. This is why an alcoholic drink turns sour if left exposed to air for a few days

Question 5

How is ethanoic acid produced by oxidation?

Answer 5

1. Oxidation by acidified potassium manganate(VII) (turns purple to colourless)
2. Oxidation by atmospheric oxygen in the presence of bacteria

Question 6

What is a possible catalyst for esterification?

Answer 6

Concentrated sulfuric acid