C6.2 Organic Chemistry Flashcards
Hydrocarbons
Compounds that only contain hydrogen atoms and carbon atoms
Release carbon dioxide when burnt
Example: coal
Alkanes
Hydrocarbons
Saturated - each carbon is bonded to another carbon by a single covalent bond
General formula CₙH₂ₙ₊₂
Names ending in “ane”
First 5 alkanes
. H
. |
Methane CH4 : H - C - H
. |
. H
. H H
. | |
Ethane C2H6 : H - C - C - H
. | |
. H H
Propane C3H8
Butane C4H10
Pentane C5H12
How many bonds can carbon atoms form
Up to 4
How many bonds can hydrogen atoms form
Only 1
How alkanes react
Combustion when alkanes react with oxygen in the air and burn
If plentiful supply of oxygen or air complete combustion happens:
carbon atoms oxidised to carbon dioxide, hydrogen atoms are oxidised to water
Example: propane + oxygen -> carbon dioxide + water
If poor supply of oxygen or air incomplete combustion happens instead
alkane + oxygen → carbon monoxide (CO) + water
problem because carbon monoxide is toxic gas and can cause suffocation
Some carbon atoms may not be oxidised at all and released as carbon particles.
CLEAN FLAME PRODUCED
Alkenes
Hydrocarbons
Unsaturated: Contain a carbon - carbon double covalent bond, C=C that can open up in reactions and bond
General formula CₙH₂ₙ
First 4 alkenes
METHENE DOES NOT EXIST!!!
. H H
. | |
Ethene: C2H4: C=C
. | |
. H H
Propene: C3H6
. H H H
. | | |
Butene: C4H8 : H-C-C-C=C
. | | | |
. H H H H
Pentene: C5H10
EACH CARBON ATOM MUST HAVE NO MORE THAN 4 ARMS
How alkenes react
alkenes can burn in oxygen or air, and the products of combustion are the same as alkanes
SMOKY DIRTY FLAME PRODUCED
alkenes have a functional group allowing them to take part in wider range of reactions
C=C is the functional group - lets alkenes undergo addition reactions where double carbon bond opens up
Addition reactions (polymerisation of alkene monomers)
atom or group of atoms combines with a molecule to form larger molecule, with no other product.
alkenes react with bromine in addition reactions forming colourless ‘dibromo’ compounds as they are unsaturated and C=C bond can open up but alkanes cannot as they are saturated with no C=C double bond
alkene + bromine → saturated, colourless dibromo-alkane compound
Example: Ethene + bromine -> dibromoethane The alkene decolourises bromine water that can be used
. to test for saturation
. C2H4 + Br2 -> C2H4Br2
. H H H H
. | | | |
H-C=C-H + Br-Br -> H-C-C-H
. | |
. Br Br
How can an alkene become an alkane
Hydrogenation - Undergo addition reactions with hydrogen in presence of nickel catalyst
Example: Ethene + hydrogen -> ethane
. C2H4 + H2 -> C2H6
C=C carbon double bond opens up to react
Alcohols in chemistry
Functional group: -OH (hydroxyl group)
General formula: CₙH₂ₙ₊₁OH
First 5 alcohols
. H
. |
Methanol: CH3OH: H-C-O-H
. |
. H
. HH
. | |
Ethanol: C2H5OH: H-C-C-O-H
. | |
. HH
Propanol: C3H7OH
Butanol: C4H9OH
Pentanol: C5H11OH
Oxidation of alcohols
(by potassium manganate)
alcohol + oxidising agent → carboxylic acid
Carboxylic acid
general formula CₙH₂ₙ₊₁COOH
functional group: -COOH (carboxyl)
Made by adding acidified (with H₂SO₄) potassium manganate solution to alcohol and warming with water bath
Colour change from purple to very pale pink as manganate ions are reduced to manganese atoms
reactions of carboxylic acids
same as any weak acid:
Carboxylic acid + metal -> salt + hydrogen
Carboxylic acid + base -> salt + water
Carboxylic acid + carbonates -> salt + water + carbon dioxide