Organic Chemistry Flashcards
ALKANES
saturated with carbon-carbon single bonds
ALKENES
unsaturated with carbon-carbon double bonds
General formula of alkanes
CnH2n+2
General formula of alkenes
CnH2n
Alkane examples
Methane (CH4 when n=1)
Ethane (C2H6 when n=2)
Propane (C3H8 when n=3)
Alkene examples
Ethene (C2H4 when n=2)
Propene (C3H6 when n=3)
Chemical Properties of Alkanes
1) Combustion
(i) Complete combustion: presence of excess air to form
carbon dioxide and water
(ii) Incomplete combustion: presence of limited air to form
carbon monoxide & water are formed.
2) Substitution reaction
CH4 + Cl2 → CH3Cl ( chloromethane) + HCl
- only take place in the presence of ultraviolet light
3) Cracking
Large alkane molecules are cracked to form smaller alkenes and alkanes / hydrogen
Conditions: 600 °C & Al2O3 catalyst
C10H22 (alkane) → C4H8 (alkene) + C6H14 (alkane)
C10H22 (alkane) → 2C2H4 (ethene) + 2C3H6 (propene) + H2
Chemical properties of alkenes
1) Combustion
(i) Complete combustion: presence of excess air to form
carbon dioxide and water
(ii) Incomplete combustion: presence of limited air to form
carbon monoxide & water are formed.
2) Addition reaction
(i) with hydrogen (200 °C with nickel catalyst)
C2H4 (ethene) + H2 → C2H6 (ethane)
(ii) with aqueous bromine (test for unsaturated compounds)
C2H4 (ethene) + Br-Br C2H4Br2 (dibromoethane)
Aqueous bromine (reddish-brown) becomes colourless
3) Addition Polymerisation
Conditions: heat, high pressure & catalyst
C2H4 + C2H4 + … → ( C2H4) n (polyethene)
What is the functional group of alcohols?
-OH
What is the functional group of carboxylic acids?
-COOH
General formula of alcohols
CnH2n+1OH
General formula of carboxylic acids
CnH2n+1COOH
Examples of alcohols
Methanol (CH3OH when n=1)
Ethanol(C2H5OH when n=2)
Propanol (C3H7OH when n=3)
Examples of carboxylic acid
Ethanoic acid (CH3COOH when n=1)
How is alcohol made?
Fermentation of sugar/glucose to form ethanol
Sugar / glucose → (yeast) ethanol + carbon dioxide
C6H12O6 → 2C2H5OH + 2CO2
Conditions:
1. Yeast must be present as catalyst
2. Suitable warmth: Temp of 37ºC
(If too hot: yeast will be destroyed; if too cold: enzymes will be
inactive)
3. no O2 present in mixture
(If O2 is present: it will oxidised the ethanol to ethanoic acid)
How is carboxylic acid made?
Oxidation of ethanol to form ethanoic acid.
Oxidation by
(i) oxygen in air or
(ii) by acidified potassium manganate(VII)
(KMnO4 will change from purple to colourless. This is
a test for alcohols)
Chemical properties of alcohol
1) Combustion
2) Oxidation to form carboxylic acid
C2H5OH (ethanol) → [O] CH3COOH (ethanoic acid)
Oxidation by
(i) oxygen in air or
(ii) by acidified potassium manganate(VII)
(KMnO4 will change from purple to colourless. This is a test for
alcohols)
Chemical properties of carboxylic acid
1) Combustion
2) Reacts like (weak) acid
- reacts with alkali to form salt & water.
- reacts with carbonates to form salt, water & CO2
- reacts with reactive metals to from salt & H2
Using a named reagent, describe how you would be able to distinguish
unsaturated hydrocarbons from
saturated hydrocarbons.
Reagent used is aqueous bromine.
If saturated hydrocarbon is present,
aqueous bromine remained brown /
no visible change.
If unsaturated hydrocarbon is
present, brown aqueous bromine
will turn colourless / brown aqueous bromine will decolourise.
Briefly describe the
manufacture of alkenes from long-chain alkanes
Alkenes can be obtained from longchain alkanes by cracking.
Using heat, high pressure and
Al2O3 catalyst, large alkane molecules are cracked to form
smaller alkenes and alkanes and
hydrogen
For example:
C10H22 (alkane) → C4H8 (alkene) +
C6H14 (alkane)
Describe the importance
of cracking.
Cracking helps to meet the demands for smaller, more useful
alkene molecules like the petrol.
Cracking is also important to
produce hydrogen.
