Organic chemistry

Question 1

What is a homologous series?

Give two examples of a homologous series.

Answer 1

It is a series of molecules that have a general formula.

The alkanes and alkenes.

Question 2

Alcohols contain which functional group?

If one hydrogen molecule from each alkane is replaced with this functional group, what do we get?

Answer 2

-O-H

A homologous series of alcohols

Question 3

What is the structural formula of…
Methanol?
Ethanol?
Propanol?

Answer 3

Methanol - CH3OH
Ethanol - CH3CH2OH
Propanol - CH3CH2CH2OH

Question 4

Carboxylic acids contain which functional group?

Answer 4

-COOH

Question 5

What is the structural formula of…
Methanoic acid?
Ethanoic acid?
Propanoic acid?

Answer 5

Methanoic acid - HCOOH
Ethanoic acid - CH3OOH
Propanoic acid - CH3CH2COOH

Question 6

Esters contain which functional group?

An ester is formed if the H atom in the -COOH- group of a carboxylic acid is replaced by what?

Answer 6

-COO-

A hydrocarbon group

Question 7

What is the structural formula of ethyl ethanoate?

Answer 7

CH3COOCH2CH3

Question 8

When an alcohol burns completely in air what are the products?

Answer 8

Carbon dioxide and water

Question 9

Give four uses of alcohols.

Answer 9

1) Alcohols with smaller molecules mix well with water and produce neutral solutions.
2) Solvents - many organic substance dissolve in alcohols.
3) Alcoholic beverages - ethanol is the main alcohol in wine, beer an other alcoholic drinks.
4) Used a s fuels in spirit burners or combustion engines, the can be mixed with petrol.

Question 10

When sodium reacts with an alcohol, what gas is produced?

How does this reaction compare to the reaction between sodium and water?

Answer 10

Hydrogen

It is lees vigorous

Question 11

How can alcohols be oxidised and what is the product of this reaction?

Answer 11

They can be oxidised by oxidising agents such as potassium dichromate to produce carboxylic acids and ethanol can be oxidised by some microbes in air to produce ethanoic acid.

Question 12

What will ethanoic acid do to alcoholic drinks and in which substance is it the main acid?

Answer 12

It will turn alcoholic drinks sour

Vinegar

Question 13

What happens when a carboxylic acid is added to water?

Answer 13

They dissolve in water to produce solutions with a pH of less than 7.

Question 14

What are the products when carboxylic acids are reacted with alcohols and what substance must be used as a catalyst in this reaction?

Answer 14

The products are an ester and water.

The reaction is conducted in the presence of an acid catalyst.

Question 15

What term is used to describe esters, what makes them appropriate to use as flavourings and in perfumes.

Answer 15

Volatile compounds

They have distinctive smells

Question 16

Why are carboxylic acids weak acids?

In aqueous solutions of equal concentration how are weak acids different from strong acids?

Answer 16

When carboxylic acids dissolve in water the do not ionise completely and some of the carboxylic acid molecules remain as molecules in the solution.
Acids that do not ionise completely are known as weak acids.

Weak acids have a higher pH and react more slowly than strong acids.

Question 17

Give advantages and disadvantages of the use of organic molecules?

Answer 17

Advantages:
1) Carboxylic acids and esters are important organic chemicals that have many uses, in foods, in drinks, as solvents and as fuels for the benefit of society.
2) Biofuels offer an alternative to fossil fuels and may help to solve problems with diminishing resources and climate change.
Disadvantages
1) Alcoholic drinks and solvents can be abused which can lead to health and social problems.
2) Some of the crops used in the production of biofuels require the use of agricultural land which could be used to grow food.