Recently in Science, we have been studying Organic Chemistry. This consists of balancing equations, alkanes, alkenes, alcohols, carboxylic acids, esters, combustion reactions, addition reactions, reactions with hydrogen, functional groups/ homologous series, reactions with sodium and ways of making ethanol.
A functional group is what gives a family of organic molecules their characteristic reactions. A homologous series is organic compounds with the same functional group. Therefore, the functional groups for the following are as below: -an alkane is C-C
-an alkene is C=C
-an alcohol is -OH
-a carboxylic acid is -C
O-H
Alkane- the general formula for an alkane is C n H 2 n+2
Alkene- the general formula for an alkene is C n H 2 n

Questions:
Using the information above, answer the questions below
1. How many hydrogens would an alkane with 18 carbons have?
2. How many carbons would an alkene with 42 hydrogens have?
3. How many carbons would an alkane with 36 hydrogens have.
4. How many hydrogens would an alkene with 12 carbons have?

Answers:
1. 38 hydrogens
2. 21 carbons
3. 16 carbons
4. 24 hydrogens

-The first four alkanes are methane, ethane, propane, butane.
-The first three alkenes are ethene, propene and butene.
-The first four alcohols are methanol, ethanol, propanol, butanol.
-The first four carboxylic acids are methanoic acid, ethanoic acid, propanoic acid and butanoic acid

Tip!
Use the phrase “ Monkeys Eat Peanut Butter” to help to remember the prefixes for these molecules.

Combustion reactions
A combustion reaction is where a hydrogen reacts with oxygen to produce carbon dioxide and water.
For example:

Ethanol + oxygen → carbon dioxide + water
2C2H5OH + 6O2 → 4CO2 + 6H2O

Question:
Write a word and balanced symbol equation for the combustion reaction of propane.

Answer:
Propane + oxygen → carbon dioxide + water
C3H8 + 5O2 → 3CO2 + 4H2O

What makes a strong acid?
– All acids make H+ ions in water.
– Strong acids are fully ionised in water to form H+ ions, therefore more H+ ions are formed.

What makes a weak acid?
– Only partially ionised to form H+ ions, therefore less H+ ions are formed.

Esters
– Carboxylic acids react with alcohols to make esters.
The general equation is:

Carboxylic acid + alcohol —> ester + water

Alkanes are saturated because they only have single bonds whereas alkenes are unsaturated because they contain both single and double bonds.

Addition Reactions
In addition reactions, alkenes lose their double bonds to become alkanes. For example:
Ethene + bromine → dibromoethane
C2H4 + Br2 → C2H4Br2

Reaction with hydrogen
Example: Ethene + hydrogen → ethane
C2H4 + H2 → C2H6
Reactions with sodium
When ethanol reacts with sodium, it effervesces. This means that it gives off bubbles of gas. The gas given off in this reaction is hydrogen. It gets smaller and smaller as it forms a solution of sodium ethoxide with ethanol.
Example: Sodium + ethanol → sodium ethoxide + hydrogen
2Na + 2CH3OH → 2CH3ONa + H2
Ways of making ethanol
Hydration of ethene and steam – ethene + steam → ethanol
C2H4 + H2O → C2H5OH
Advantages:
– It is a continuous process.
– It is a fast reaction.
– It makes pure ethanol.
Disadvantages:
– The raw materials are non-renewable.
– Needs to be in an area with a high temperature and high pressure.
– Requires a lot of energy.
Fermentation of yeast – glucose → ethanol + carbon dioxide (C6H12O6 → 2C2H5OH + 2CO2
Advantages:
– Only a little amount of energy is needed.
– The raw materials are renewable.
– It only needs to be in a warm area with a normal pressure.
– It’s a carbon neutral process.
Disadvantages:
– It’s a batch process.
– Needs to be filtered as it is impure.
– It’s a slow reaction.