Chemical Properties and Interchange Between Homologous Series

2.3

Chemical Properties and Interconversion of Compounds between Homologous Series

Chemical Reactions of Alkanes

Combustion

Combustion of alkane involves the reaction of alkane with oxygen gas in the air.
Complete combustion of an alkane is when the oxygen gas is in excess.
The products of complete combustion of alkane are carbon dioxide gas and water.
Example of the complete combustion of methane:

\(CH_4(g) + 2O_2(g) \rightarrow CO_2(g) + 2H_2O(l)\)

In the case of insufficiency of oxygen gas, the incomplete combustion of alkane occurs.
The products such as carbon monoxide and carbon might be formed from incomplete combustion of alkane.
Example of the incomplete combustion of methane;

\(2CH_4(g) + 3O_2(g) \rightarrow C(s)+CO_2(g) + 4H_2O(l)\)

\(6CH_4(g) + 9O_2(g) \rightarrow 2C(s)+2CO(g)+2CO_2(g) + 12H_2O(l)\)

Susbtitution Reaction

A chemical reaction where another atom is substituting one or more atoms in a molecule.
The substitution reaction of alkane that involves halogen is also called a halogenation reaction.
The sunlight is needed in this reaction.
The energy from the sunlight is needed to break the covalent bond in the halogen compound to form bond with halogen atoms.
Example of substitution reaction of methane with chlorin:

\(CH_4(g) + Cl_2(g) \rightarrow CH_2Cl_2(l) + H_2(g)\)

Chemical Reactions of Alkene

Combustion

Combustion of alkene involves the reaction of an alkene with oxygen gas in the air.
Complete combustion of an alkene is when the oxygen gas is in excess.
The products of complete combustion of alkene are carbon dioxide gas and water.
Example of the complete combustion of ethene:

\(C_2H_4(g) + 3O_2(g) \rightarrow 2CO_2(g)+ 2H_2O(l)\)

In the case of insufficiency of oxygen gas, the incomplete combustion of alkene occurs.
The products such as carbon monoxide and carbon might be formed from incomplete combustion of the alkene.
Example of the incomplete combustion of ethene:

\(C_2H_4(g) + O_2(g) \rightarrow 2C(p)+ 2H_2O(l)\)

atau

\(C_2H_4(g) + 2O_2(g) \rightarrow 2CO(g)+ 2H_2O(l)\)

Addition Reaction

Definition: a reaction where other atoms are added to a molecule.
The double bond in the alkene makes the compound reactive.
The addition reaction occurs at the double bond of the compound.
Five addition reactions that occur on alkenes is as stated below:

1. Addition of Halogen (Halogenation)

Reaction with halogen (chlorine, bromine) at room condition.
This reaction is also called the halogenation reaction.
Product: Haloalkane.

\(C_2H_4(g) + Cl_2(g) \rightarrow C_2H_4Cl_2(g)\)

2. Addition of Hydrogen (Hydrogenation)

Alkenes react with hydrogen at a temperature of 180 °C in the presence of nickel /platinum as a catalyst to produce the corresponding alkanes.
Catalyst: platinum, Pt or nickel, Ni.
Temperature: 180°C.
This reaction is also called a hydrogenation reaction.
Product: Alkane.

\(\, \\C_2H_4(g) + H_2(g) \xrightarrow []{Pt\,or\, Ni}C_2H_6(g)\)

3. Addition of Water (Hydration)

Alkenes react with water (in the form of steam) at high temperature and pressure, in the presence of phosphoric acid, H3 PO4 as a catalyst to produce alcohol.
Catalyst: phosphoric acid.
Temperature: 300°C.
Pressure: 60 atm.
This reaction is also called the hydration reaction.
Product: Alcohol.

\(\,\\C_2H_4(g) + H_2O(ce) \xrightarrow []{H_3PO_4}C_2H_5OH(ce)\)

4. Acidified potassium manganate(VII) solution, KMnO4

Acidified potassium manganate(VII) solution is a very good oxidising agent.
This reaction is also called the oxidation reaction.
Product: Diol (Alcohol with two hydroxyl groups).

\(C_2H_4(g) + H_2O(l) \xrightarrow []{[O]} CH_2OHCH_2OH(l)\)

Polymerisation Reaction

The pair of electrons making up one of the double bonds is shared with the carbon atom of another alkene molecule in the polymerisation reaction.
Example: polymerisation of ethene:
- Polymer: polyethene.
- Monomer: ethene.
- Pressure: 2000 atm.
- Temperature: 100°C to 300°C.

Penyediaan Etanol

Production of Ethanol in the Indutry

Addition reaction with water (steam)
- Catalyst: phosphoric acid.
- Temperature: 300°C.
- Pressure: 60 atm.
\(C_2H_4(g) + H_2O(l) \xrightarrow[]{H_3PO_4} C_2H_5OH(l)\)

Production of Ethanol in the Laboratory

The fermentation process of carbohydrate or sugary substances like rice, barley or fruits
- These substances contain glucose.
- Zymase in yeast acts as a catalyst to convert glucose to ethanol.
- \(C_6H_{12}O_6(aq) \xrightarrow[]{yis} 2C_2H_5OH(l) + 2CO_2(g)\)

Chemical Properties of Ethanol

Combustion

Combustion of ethanol in excess oxygen produces carbon dioxide and water.
\(C_2H_5OH(l) + 3O_2 (g) \rightarrow 2CO_2(g) + 3H_2O(l)\)

Oxidation

Ethanol is oxidised by acidified potassium dichromate(VI) solution.
Product: ethanoic acid
Dichromate ion (orange) changes to chromium ion (green).
\(C_2H_5OH(l) \xrightarrow[]{[O]} CH_3COOH(l)\)

Dehydration

A water molecule is eliminated from the reaction.
Catalyst: sulphuric acid.
Temperature: 180°C.
Product: ethene.
\(C_2H_5OH(l) \xrightarrow[]{H_2SO_4, 180^\circ C} C_2H_4(g) + H_2O(l)\)

Preparation of Ethanoic Acid in the Laboratory

Oxidation of ethanol
- Ethanol is oxidised by acidified potassium dichromate(VI) solution.
- Dichromate ion (orange) changes to chromium ion (green).
\(C_2H_5OH(l) \xrightarrow[]{[O]} CH_3COOH (l)\)

Chemical Reactions of Ethanoic Acid as An Acid

Reaction with Base or Alkali

Product: salt and water
Also known as neutralisation reaction.
Example of reaction with sodium hydroxide:
\(CH_3COOH (aq) + NaOH(aq) \rightarrow CH_3COONa (aq) + H_2O(l)\)

Reaction with Reactive Metal

Product: salt and hydrogen gas
Example of reaction with magnesium:
\(2CH_3COOH (aq) + Mg(s) \rightarrow (CH_3COO)_2Mg (aq) + H_2(g)\)

Reaction with Metal Carbonate

Product: salt, carbon dioxide gas and water
Example of reaction with calcium carbonate:
\(2CH_3COOH (aq) + CaCO_3(s) \rightarrow (CH_3COO)_2Ca(aq) + H_2O(l) + CO_2(g)\)

The Chemical Reaction of Ethanoic Acid with An Alcohol

Product: ester.
Also known as an esterification reaction.
Catalyst: hydrogen ion.
\(CH_3COOH (aq) + C_2H_5OH(l) \xrightarrow []{H^+}CH_3COOC_2H_5(aq) + H_2O(l)\)

Ester

Functional group: carboxylate group, \(-COOC-\)
General formula: \(C_nH_{2n+1}COOC_mH_{2m+1}\), where n = 0,1,2,… and m = 1,2,3,…

Naming Ester

Ester is produced by combining alcohol with carboxylic acid.
There are two parts to naming an ester.
The first part is based on the name of the alcohol.
The second part is based on the name of the carboxylic acid.
Example: Ethyl butanoate.

The diagram shows the structural formula of ethyl butanoate.

Steps in Naming An Ester

Determine the alkyl group of the alcohol chain based on the structural formula or the molecular formula.
Determine the name of the carboxylic acid part.
Change the term ‘oic’ in carboxylic acid to ‘oate’.

Preparation of Ethyl Ethanoate in Laboratory

Mixing ethanoic acid with ethanol by reflux reaction.
Reflux is needed because ethanol is a volatile solution.
\(CH_3COOH(aq)+ C_2H_5OH(aq) \xrightarrow[]{ H_2SO_4} CH_3COOC_2H_5(aq)+H_2O(l)\)

Physical Properties of Ethyl Ethanoate

A colourless solution at room temperature.
Nice fruity smell.
Soluble in water.

Esterification Ester

Product: ester.
Also known as an esterification reaction.
Catalyst: hydrogen ion.
Example of esterification reaction of ethanoic acid with ethanol:
\(CH_3COOH(aq)+ C_2H_5OH(aq) \xrightarrow[]{ H_2SO_4} CH_3COOC_2H_5(aq)+H_2O(l)\)

Natural Sources of Ester
Flower or Fruit	Ester
Jasmie	Benzyl ethanoate
Pear	Propyl ethanoate
Apricot	Pentyl propanoate
Kiwi	Methyl benzoate
Pineapple	Ethyl butanoate
Banana	3-methylbutyl ethanoate