What is a functional group ?
a group of atoms common in all molecules of a homologous series.
What is a homologous series ?
a ‘family’ of molecules with the same functional group that have characteristic reactions.
What is the general formula of alkenes ?
C(n)H(2n)
If there were 5 carbon atom in an alkene, how many hydrogen atoms would there be, and what would the name of the molecule be ?
- pentene
- 10 hydrogen atoms
What bond must an alkene have ?
carbon to carbon double bond (C=C)
What do the alkenes look like during combustion ?
burn incompletely with smoky, yellow, luminous flame.
What does ethene’s reaction with bromine water look like and why ?
- bromine water is orange
- ethene added then mixture shaken
- bromine water decolourised and dibromoethane is formed
- decolourised because ethene uses bromine to saturate itself and achieve a structure like an alkane
How do you make an alkane out of an alkene ?
- react alkene with hydrogen to saturate it
- reaction takes place at 60’C with nickel catalyst
How do you make an alcohol from an alkene ?
- react alkene with steam and a catalyst (reversible reaction)
What is the functional group of an alcohol ?
-OH
What is the functional group of a carboxylic acid ?
-COOH
What is the functional group of an ester ?
-COO-
Name two ways to make ethanol (give word equations as well).
REACTION WITH STEAM:
ethene + steam -(catalyst)-> ethanol
FERMENTATION:
glucose -(yeast)-> ethanol + carbon dioxide
How are alcohols used ?
- as solvents (perfumes, aftershaves, mouthwashes)
- as drinks
- as fuel (methylated spirits)
- to make carboxylic acids
How does ethanol burn ? (give word equation)
- with a clean blue flame
- ethanol + oxygen -(heat)-> carbon dioxide + water
How do alcohols react when sodium is added ? What is formed ?
- effervescence (not as vigorous as with water)
- produces hydrogen gas
- gets smaller as it dissolves in the alcohol
- sodium alkoxide solution is formed (eg. sodium ethoxide)
How is a carboxylic acid formed (2 ways) ?
BOILING WITH CHEMICAL OXIDISER:
ethanol + oxygen atoms from oxidising agent (potassium dichromate) -> ethanoic acid + water
LEAVING ALCOHOL OUT IN AIR:
- ethanol left out in air will be broken down by microbes in the air to ethanoic acid
Why are carboxylic acids weak acids ?
- H+ ions do not ionise fully in solution
- lower concentration of H+ ions than strong acids
How is an ester made ?
carboxylic acid + alcohol -(acid catalyst)-> ester + water
What are the properties of esters ?
- sweet/fruity smells (good for foods + perfumes)
- volatile
