Chapter 19 + 20 - Hydrocarbons + Alcohols, Carboxylic Acids and Ester

Homologous series

Family of organic compounds with the same functional group

1. Characteristics

   • Same general formula

   • Similar Chemical properties as they have the same functional group

   • Diff by CH2

   • Gradual change in physical properties

Alkanes

1.Functional Group

• Saturated hydrocarbons that contain only carbon-carbon single covalent bonds

• C_nH_2n+1

• As molecule increase, melting/boiling point , viscosity and flammability increases

  • As molecule size increases, there is a stronger intermolecular forces of attraction between molecules

  • Hence more energy need to overcome/flow less easily

2. Reaction of Alkanes

   • Combustion

     • Burning in excess oxygen to produce carbon dioxide and water

     • Is highly exothermic

   • Substitution reactions

     • Reaction with halogens in the present of ultraviolet light

     • A hydrogen atom is replaced/substituted by a halogen

Alkenes

1. Functional Group

   • Hydrocarbons that contain one or more carbon-carbon double bonds

   • Any molecule that contains carbon-carbon double bond (or triple) is describe as unsaturated

   • C_nH_2n

   • As molecule increase, melting/boiling point , viscosity and flammability increases

     • As molecule size increases, there is a stronger intermolecular forces of attraction between molecules

     • Hence more energy need to overcome/flow less easily

2. Reaction of Alkenes

   • Combustion

   • Addition reactions

     • with hydrogen (heat at 150,nickel catalyst)

       • Used to produce margarine from vegetable oil (polyunsaturated fat)

       • ethene → ethane

     • with aqueous bromine (room temp and pressure)

       • test for alkane/alkene

       • In alkene it will decolourize reddish-brown rapidly

     • with steam (heat at high pressure (300, 60atm) with concentrated H₃PO₄ (Phosphoric acid)

       • Alkenes → alcohol

   • Addition Polymerisation

     • High temp, high pressure and presence of catalyst

     • Forms a large molecule called a polymer

Cracking

Breaking down of long-chain hydrocarbons molecules into smaller hydrocarbons molecules

• High temp (600) and aluminium oxide or silicon dioxide as a catalyst

• Importance of cracking

  • Forms shorter-chain alkenes which are important materials for important industrial processes

  • Shorter-chain alkanes which are high in demand

Isomerism

Compounds that have the same molecular formula but different structural formula

1. Chain Isomerism

   • Straight chain (unbranched)

   • branched

2. Positional Isomerism

   • functional group is connected to a different carbon atom

3. Functional group isomerism

   • Same molecular formular but a different functional group

Alcohols

1. Functional Group

   • Organic compounds which have the hydroxyl (OH) functional group

   • C_nH_2n+1OH

2. Physical Properties

   • Volatile Liquids

   • Soluble in Water

     • Alcohols with a short hydrocarbon chain are very soluble

   • Increasing melting and boiling point

     • Size of molecule increases becomes larger. Hence, the strength of the intermolecular forces of attraction between the molecule increases, resulting in increasing melting and boiling points down the homologous series

3. Chemical Reactions

   • Combustion

     • Highly exothermic

     • Produces water

   • Oxidation by atmospheric oxygen

     • Alcohol + Oxygen → Acid + Water

   • Oxidation using oxidizing agent

     • Acidified KMno4

     • Heat under reflux

     • Produces water

     • Colour change of purple to colourless

   • Addition reaction with ethene

     • Steam, heated at high pressure and concentrated phosphoric(V) acid (H3PO4)

Fermentation

• Yeast act on carbohydrates(glucose) in the absence of oxygen 37°C

• Producing alcohol + carbon dioxide

• 37°C must be used as enzymes will denature and unable to catalyse the reaction

• The stopper ensures the absence of oxygen in order to prevent the oxidation of ethanol into ethanoic acid by bacteria from the air

• Limewater acts as an air lock to allow carbon dioxide to escape and to prevent oxygen from entering the set up

• It is impossible to make pure ethanol by fermentation as yeast is killed when the mixture contains more than 15% ethanol

• Ethanol can be extracted by fractional distillation allowing for higher concentration to be produced

Carboxyllic acids

1. Functional group

   • C_nH_2n+1COOH

2. Physical properties of Carboxylic acid

   • Very soluble in water

   • Melting point and boiling point increases down the group

   • Conducts electricity when dissolved in water due to mobile electrons

3. Chemical Reactions

   • Acid + Metal →Salt + Hydrogen

   • Acid + Metal Carbonate →Salt + Carbon Dioxide + Water

   • Acid + Base →Salt + Water

     • Acid + Alcohol ⇌ Ester + Water

Esters

1. What are they

   • Sweet-smelling, colourless liquid that are insoluble in water

   • Contains -COO- functional group

2. Esterification

   • Acid heated with alcohol in the presence of a few drops of concentrated sulfuric acid as a catalyst