Organic Chemistry - GCSE Chemistry AQA

Specification 4.7

Hydrocarbons

Any compound formed only from carbon and hydrogen atoms

How many bonds do Carbon atoms form

4 strong bonds - commonly hydrogen

Alkanes

Alkanes are the most simple and common type of hydrocarbon

Homologous series; Methane CH4, Ethane C2H6, Propane C3H8, Butane C4H10

General formula: CnH2n+2

Saturated compounds meaning each carbon atom has 4 single covalent bonds - no double bonds

Properties of Alkanes 

Boiling point increases with chain length 

Shorter alkanes are more volatile (evaporate easily)

Longer are more viscous - thick and sticky

Shorter alkanes are more flammable 

Uses of Alkanes

One of main uses is fuel as they release energy when burnt with oxygen - combustion
Complete combustion happens when enough oxygen is present

Hydrocarbon + Oxygen ——> Carbon Dioxide + Water

Hydrocarbon is oxidised

Lots of energy released as it is an exothermic reaction

Crude Oil

Non renewable fuel

• Finite resource - formed over millions of years from the remains of ancient sea creatures (mainly plankton) - buried in mud

• High pressure and high temperature in absence of oxygen makes crude oil 

• Mixture of hydrocarbons - each with different properties + boiling points and uses 

• Petrochemicals (substances from crude oil) - used as feedstock - Solvents, polymers, lubricants and detergents

Fractional Distillation 

Used to separate hydrocarbons in crude oil, each with different properties and are used for different things 

Crude oil is heated up until it turns to gas then it is fed into fractionating column (hot at the bottom and cool at the top)

• Gas rises up column and each hydrocarbon condenses at boiling point

• Different fractions are collected as liquids at different levels 

• Long chain hydrocarbons condense near bottom as they have higher boiling points

• Shorter chain hydrocarbons condense nearer the top as they have lower boiling points 

Long Chain Hydrocarbons

• Bitumen (used for roads)

• Heavy fuel oil (used for lubricating, fuel and heating oil) 

• Are bad fuels - Can be broken down into shorter chain hydrocarbons which are more useful through cracking

Short chain Hydrocarbons

• Burn with cleaner flames - most flammable best fuels

• Diesel + Petrol (used in cars)

• Kerosene (used in jet engines)

• Some hydrocarbons never liquify and stay gas at room temperature - E.g: LPG

Cracking - Catalytic Cracking 

Thermal decomposition reaction 

Catalytic Cracking - Heat and vaporise long chain hydrocarbons - The vapour is passed over hot powdered aluminium oxide - The catalyst split apart long chain hydrocarbon into shorter, more useful ones

Cracking - Steam Cracking

Long chain hydrocarbon vapour is mixed with steam and heated at a high temperature causing chain to split

Equation for Cracking

Long chain Alkane ——> Shorter Alkane + Alkene
Same amount of hydrogen and carbon on each side

Alkenes

C=C Functional group 

• Used to produce polymers 

• Homologous series (like alkanes)

• Doubles bonds + unsaturated

• More reactive as they are unsaturated

• Can be added together to make polymers - double bonds can break to form 2 or more bonds in addition reactions

• General Formula: Cn2n

Test for Alkenes 

React with Bromine 

• mix bromine water with solution of alkenes - bromine water turns from orange to colourless 

3 Types of Addition reactions

Hydrogenation

Hydration

Halogenation

Hydrogenation

Alkene + Hydrogen ——> Alkane

Presence of catalyst 

Double bond in Alkene breaks apart and Hydrogen atoms bonds to carbons to make saturated alkanes (no double bonds)

E.g: Propene + H2 ---> Propane

Hydration 

Water heated up to make water vapour 
Alkene + Water ---> Alcohol 

Presence of  (phosphoric acid) catalyst, high temperature and pressure

 H + OH bond to carbon atoms as double bonds break apart E.g: Ethene + Water ----> Ethanol (used for alcoholic drinks + industrial processes)

-  Needs to be separated from unreacted ethene (which has lower boiling point) and Water  

Therefore cool down mixture as ethene will stay as gas and water + ethanol will condense - Fractional distillation used to separate water from ethanol to get pure ethanol 

Halogenation 

Alkene + Halogen ——> Alkane

Presence of Catalyst 

Double bond in Alkene breaks apart and Hydrogen atoms bonds to carbons to make saturated alkanes (no double bonds)
Halogen usually Bromine 

Combustion with Alkenes

Alkenes burn with smokier yellow flame as there is INCOMPLETE COMBUSTION - when ethene gas is tested with lighted spill

Release less energy

Burning Crude oil fractions

Burning crude oil fractions can release sulphur dioxide (SO₂) because crude oil contains sulphur impurities that react with oxygen during combustion, forming SO₂ gas

Nitrogen oxides (NOx) are released when high combustion temperatures cause nitrogen from the air to react with oxygen. 

Incomplete Combustion 

When fossil fuels are burnt but there is not enough oxygen - Carbon monoxide CO is formed - Toxic colourless + odourless - red blood cells pick it up in place of oxygen and carry in blood around body

Carboxylic acids

homologous series of organic compounds
Functional group: COOH (always at the end): Methanoic acid, Ethanoic acid, Propanoic acid, Butanoic acid

• Order: HCOOH, CH3COOH, C2H5COOH, C3H7COOH

• All weak acids - don’t fully ionise  in water - Carboxylic acids don’t release all their hydrogen ions

• C2H5COOH ------> <------ C2H5COO- + H+ : Reversible reaction- negative ions: anoate ending (e.g: propanoate ion) 

• Carboxylic acid + Metal carbonate -----> salt + water + carbon dioxide - e.g: ethanoic acid + potassium carbonate -----> potassium ethanoate + water 

• Carboxylic acids made by oxidising alcohol - Alcohol ------> (oxidising agent) carboxylic acid + water - e.g: butanol ---> butanoic acid + water

Esters

Functional Group: -COO- always in the middle of the molecules 

• Have pleasant (sweet or fruity) smells 

• Volatile and evaporate easily

• For this reason found in perfume and food flavourings 

• To make esters: Carboxylic acid + alcohol -----> (acid catalyst- usually concentrated sulfuric acid)  Ester + water molecule - e.g: ethanoic acid (loses OH) + ethanol (loses Hydrogen from OH group) -----> ethyl ethanoate + water molecule (byproduct) (together the OH from ethanoic acid and the Hydrogen from Ethanol makes a water molecule)

• Ethyl ethanoate (CH3COOC2H5) - COO is ester link linking acid and alcohol

Alcohols

Another homologous series of organic compounds 

• Look almost the same as alkanes expect have an OH functional group in place of one the hydrogens 

• Methanol, ethanol, propanol, butanol

• Formulas: CH3OH, C2H5OH, C3H7OH, C4H9OH

• General formula: CnH2n+1OH

• These four have similar properties; they are flammable - can undergo complete combustion in the air therefore can be used as fuels as when burnt they release lots of energy - alcohol + O2 -----> CO2 + H2O (then balance equation)

• They are soluble - have a neutral pH so when they are dissolved in a solution, the pH is neutral - used as solvents in industry as they can dissolve things that water can’t: For example, hydrocarbons + lipid compounds like fats and oils 

Ethanol 3 Uses

• Chemical feedstock to produce other organic  compounds (feedstock - raw materials used to provide reactants for an industrial reaction)

• Used as a biofuel (can be burned like petrol) + used in spirit burners - burns with clean blue flame 

• Used in alcoholic drinks: beer + wine + spirits 

Production of Ethanol 1

Ethanol can be produced from ethene and steam: addition reaction as water molecules are being added to ethene molecules 

• Conditions: Higher temperature (300C) and high pressure and phosphoric acid catalyst 

• C2H4 + H20 ------> C2H5OH 

• Advantages: Ethene is cheap and reaction itself is cheap and efficient 

• Disadvantages: Ethene is made from crude oil which is a non-renewable resource therefore if cruise oil begins to run out, ethene will become expensive

Production of Ethanol 2 

Ethanol can also be produced by fermentation: anaerobic respiration of sugars by yeast cells to produce ethanol and carbon dioxide 

• Carried out in fermentation tanks - requires yeast cells which have naturally occurring enzymes to catalyse the reaction 

• Conditions: Temperature - no higher or lower than 30 - 40 degrees Celsius as that temperature is optimum for enzymes.

• Should be carried out in anaerobic conditions so that ethanol isn’t oxidised to ethanoic acid 

• Advantages: Sugar + glucose used is a renewable resource, yeast are easy to grow 

• Disadvantages: process can be slow: ethanol produced isn't pure - must be distilled by fractional distillation

Sodium Reaction with Alcohol

When sodium reacts with ethanol (can react with other alcohols) - sodium gives off bubbles of gas and produces hydrogen 

• Sodium gets smaller as it dissolves in alcohol producing sodium alkoxide solution 

• E.g; sodium + ethanol -----> sodium ethoxide + hydrogen 

Polymers 

Long chain molecule made of smaller chain monomers 

Addition Polymerisation

• An alkene has carbon carbon double bond therefore is unsaturated 

• Double bond can break into single bond - allowing 2 carbons to form new bonds 

• Alkene bonds can bond to each other if double bond breaks - forming long chain polymers 

• E.g: 3 etc Ethene monomers double bond breaks -------> (Catalyst and pressure) ethene monomers bond to each other to make polymer 

• These reactions sometimes involve 100s of monomers therefore drawing them out would take a long time 

• Represented with brackets (see sheet diagram) - poly in front of monomer name poly(ethene)

Condensation polymerisation

Made up of many individual polymers

• 2 Products formed - the condensation polymer and small molecule (water or hcl)

• Small molecule always formed 

• 2 Water molecules formed when forming polyester 

• Each monomers must have at least 2 functional groups 

• 2 Different functional groups overall

Forming Polyesters

• Polyester - commonly use 2 different monomers 

• Dicarboxylic acid monomer + diol monomer 

• Dicarboxylic acid contains 2 carboxylic acid groups 

• Diol monomer contains 2 alcohol groups 

• Dicarboxylic acid gives up OH group from one of the carboxylic acid groups and diol monomer gives up one H from OH group from one of the alcohol groups

• These bond together to form water molecule - and leaves the Carbon (from dicarboxylic acid) and Oxygen (from diol) to bond together to form a polyester (bond via ester link - COO - ) - This forms a dimer (only 2 monomers) - to show repeat unit the H and OH on the ends are removed and form another water molecule 

• Process often happens with 100s or 100s of monomers - n represents amount of monomers  - N goes before both reactants and after condensation polymer repeat unit and in 2nH2o 

• Polyesters - generally biodegradable as bacteria can break down ester links - big difference to non-biodegradable additions polymers, like plastics

Nylon

condensation polymer - small molecule: hydrogen chloride 

• High tensile strength - strong intermolecular forces between its polymer chains

Naturally occurring polymers: 3 Types 

aren’t man made

DNA

Polypeptides 

Carbohydrates 

DNA

Made up of nucleotides (Polynucleotides)

Contain different orders of nucleotides which code for different genes

2 polymer chains in a double helix shape to prevent them from getting damaged

4 types of nucleotides as there are 4 types of Bases (TACG)

Polypeptides/Protein

• Polypeptides are lots of different amino acids that combine in many different combinations - many different proteins 

• Proteins catalyse chemical reactions as enzymes 

• Provide structure + Strength to tissue 

Amino acids: 2 functional groups: Amino group and Carboxyl group and R group (changes depending on each amino acid as each amino acid is different)

Allow adjacent amino acids to join together through condensation reactions - producing small water molecules (OH from carboxyl and H from amino group remove (water molecule)) allowing carbon and nitrogen to bond - bond is called amide bond, amide link or peptide bond

Carbohydrates 

Carbohydrates

• Many different polymers and monomers - used to get energy in our body

• Made of carbon, oxygen and hydrogen

• Polymers (polysaccharides) - starch, cellulose, glycogen 

• Monomers (monosaccharides) - glucose, fructose - by combining together polymer starch is made