Homologous Series Flashcards
Complete Combustion
React with excess air to give carbon dioxide and water
Incomplete Combustion
React with limited air to give carbon (soot), carbon monoxide and water
Cracking
Long chain/large alkane molecules are cracked to form smaller alkenes and alkanes/hydrogen gas
Substitution
React with halogens to replace 1 hydrogen atom with a halogen atom in presence of UV light
Uses of Cracking
- convert not so useful long chain alkanes to smaller and more useful short chain alkanes that are high in demand
- produce alkene molecules
- produce hydrogen gas
Addition of Hydrogen/Hydrogenation
Conditions: 200 degrees Celsius, Nickel catalyst, converts alkenes to alkanes
Application: Adding hydrogen to vegetable oil (polyunsaturated) to form margarine (polysaturated)
Alkanes
saturated with carbon-carbon single bonds
Alkenes
unsaturated with carbon-carbon double bonds
Addition of Bromine/Bromination
Test for unsaturated compound (alkene)
Observation: reddish-brown aqueous bromine decolourises
With alkanes: aqueous bromine remained reddish-brown
Addition of Steam/Hydration
Conditions: 300 degrees Celsius, 60 atm pressure, H3PO4/phosphoric (V) acid
Alkene + Water -> Alcohol
[Converts Alkene to Alcohol[
Oxidation
Reagent: Acidified potassium manganate (VII), KMnO4
Conditions: Heat
[Converts Alcohol to Carboxylic Acid]
Observation: Purple KMnO4 decolourises
Esterification
Reagent: Alcohol & Carboxylic Acid
Conditions: Heat, concentrated sulfuric acid/H2SO4 catalyst
[Converts alcohol and carboxylic acids to esters]
Ester name trend:
Alcohol + Acid
Properties of Esters
Colourless oily liquids with a sweet fruity smell, immiscible and less dense than water.
Addition of Steam to Ethene to produce Alcohol
Reagent: Ethene and H2O (g)
Conditions: 300 degrees Celsius, 60 atm pressure, phosphoric (V) acid
C2H4 (g) + H2O (g) -> C2H5OH (l)
Advantages:
1) High yield of ethanol
2) Shorter time to produce ethanol
Disadvantages:
1) Expensive process to maintain high temp & pressure
Fermentation of Glucose to produce Alcohol
Reagent: glucose
Conditions: 37 degrees Celsius, absence of air, yeast
C6H12O6 -> 2C2H5OH + 2CO2
Advantages:
1) Raw materials easily available
2) Conditions for fermentation easily achieved
Disadvantages:
1) Ethanol only produced after a few days
2) Low yield of reaction
3) Distillation required to separate ethanol from mixture
