Alkanes

- Most hydrocarbons obtained from petroleum are alkanes.
- Alkanes are saturated hydrocarbons, which only contain single C-C bonds and are compounds that contain carbon and hydrogen.
- Naming alkanes:
1. meth - Monkeys
2. eth - eat
3. prop - peanut
4. but - butter
5. pent - poorly

e.g. C₂H₆ = ethane

HOMOLOGOUS SERIES:

- Alkanes are an example of a homologous series.
- Homologous series members have:
    1. Similar chemical properties
    2. Same functional group
    3. Same general formula

FORMULAE: (organic molecules only)

- Molecular formula: Gives the exact number of atom(s) of each element present in a molecule.
- Displayed formula: Shows arrangement of atoms—uses lines to represent covalent bonds between atoms.
- Structural formula: Shows arrangement of atoms without using lines to represent covalent bonds between atoms.
- General formula: Shows the simplest algebraic formula of a member of a homologous series.

E.g. Propane:
- Molecular formula - C₃H₈
- Displayed formula -

- Structural formula - CH₃CH₂CH₃

GENERAL FORMULA:
- For all alkanes = C_nH_2n+2

PHYSICAL PROPERTIES:
- The boiling point is the temperature at which an alkane transitions from a liquid to a gas.
- As the chain of alkane increases, so does the boiling point: the strength of the intermolecular forces increases between alkane molecules. 
- Volatility: The ease with which a substance transforms into a gas (a lower boiling point indicates greater volatility).
As the alkane chain gets longer, volatility decreases.
Flammability: How easily something ignites.
Flammability decreases as the alkane chain grows longer. 
- Viscosity: The degree to which something flows easily (higher viscosity = more difficult to flow).
The value increases as the chain lengthens.

PROPERTIES:
- Methane = Colourless gas 
- Propane = Colourless gas
- Pentane = Colourless liquid 
- Diesel oil = Yellow liquid

The colour becomes dull as the chain lengthens.

Note: The bigger the Mr, the stronger the IM forces.

Crude Oil 

- Crude oil/petroleum is a fossil fuel—it's remains of an ancient biomass consisting mainly of plankton buried in mud.
- Crude oil is still forming very slowly under the oceans, but we're using it up much faster than it can form—it may run out.
→ Oil is a non-renewable, finite resource.
- Crude oil = A mixture of hydrocarbons
→ Two or more substances are not chemically bonded.

- Geologists and geophysicists use seismic surveys to find crude oil under the ground.
- The process involves using an air gun.
- Then a rig is placed in the hole.
- A steel pipe is placed in the hole. 
→ There is a very high pressure and flammability of the oil; this can be very dangerous.

REFINING PETROLEUM OIL

- Petroleum contains 100s of different hydrocarbon compounds, which are made of molecules that vary in size from those that contain 1/2 carbon atoms to those that contain 100 carbon atoms.
- Petroleum is separated into groups of compounds that have molecules of similar size.
→ The liquids are separated by fractional distillation, as each compound has a different boiling point.

REFINING AND SEPARATING OIL

When the mixture is heated, the compounds. start to evaporate.
The shortest-chain alkane evaporates first because it has the lowest boiling point.
The cold water is to turn the gas back to a liquid condensation.

The obtained liquid, known as the distillate, represents one fraction of the crude oil.
The temperature will rise once all of this compound has boiled off, allowing for the extraction of further fractions.

Fraction → One component/hydrocarbon from crude oil

FRACTIONAL DISTILLATION:

1. Crude oil enters the fractionating column as a vapour.
2. The fractionating column is hotter at the bottom and cooler at the top.
3. Hydrocarbons condense when the temperature drops below their boiling point.
4. Long chain hydrocarbons condense at the bottom.
5. Short chain hydrocarbons condense at the top.

Types of Combustion

Complete Combustion:
- In plentiful supply of oxygen
- Fuel + Oxygen → Carbon dioxide + Water
- Problem = Release of CO₂ greenhouse gases are increasing global warming. 

- E.g., Combustion of propane + Butane:
- C₃H₈ + 5O₂ → 3CO₂ + 4H₂O
- C₄H₁₀ + 6.5O₂ → 4CO₂ + 5H₂O

Incomplete Combustion:
- When fuel burns in an insufficient supply of oxygen.
→ Two reactions can occur. 
1. Fuel + Oxygen → Carbon monoxide + Water
- Carbon monoxide is a toxic gas that reduces the oxygen-carrying capacity of the blood.
- You can prevent CO from forming by ensuring there's a good supply of O₂ + lots of ventilation anywhere you burn fuels.

2. Fuel + Oxygen → Carbon + Water
- Carbon particulates/soot are formed. 
→ Black powder causing respiratory problems (and global dimming).

1. C₂H₄ + 2O₂ → 2CO + 2H₂O
- C₄H₈ + 4O₂ → 4CO + 4H₂O

2. C₂H₄ + O2 → 2C + 2H₂O
- C₄H₈ + 2O₂ → 4C + 4H₂O

Combustion of Alkanes:

- Alkanes, a substance that burns to release energy, are FLAMMABLE. FUEL is alkane, and if you burn it, it'll react with oxygen.

Combustion Equation
- Hydrocarbon + Oxygen → Carbon dioxide + Water 
in the air → as a gas 
- Wax is also a hydrocarbon - C₂₁H₆₄

In alkanes, each carbon atom contains four single covalent bonds: alkanes are fairly inert, and there are a few reactions they readily undergo.

- The reaction being shown is highly flammable, which means it will release energy.
- Combustion reaction = A reaction that releases heat. Burns to release energy = An exothermic reaction. Chain alkanes are good as a fuel. When a hydrocarbon fuel burns, it reacts with oxygen in the air to form CO₂ + H₂O.

- In the U-tube, we condense coming.
- The formed liquid turns the blue cobalt chloride paper pink.
- The limewater turns cloudy and milky. 
- Alkanes flammability → Reliance on alkanes as fuel:
E.g., Easy and cheap to get hold of, as methane and propane gases are easily transported, and solid fuels can be transported relatively easily, diesel and kerosene are used as vehicle fuels.

Problems from Burning Fuel 

- There are sometimes sulphur impurities in fuel.
→ When you burn the fuel, sulphur will also burn.
- Sulphur + Oxygen → Sulphur dioxide
- SO₂ gas rises in the air and reacts with water vapour in the clouds to form sulphurous acid.
- Sulphur dioxide + Water → Sulphurous acid
- SO₂ + H₂O → H₂SO₃

The temperatures in an engine get very high. When you burn the fuel, the high temperature causes nitrogen in the air to react with oxygen.
- Nitrogen + Oxygen → Nitrogen oxides
- N₂ + O₂ → NOx
- Nitrogen oxides are gases that rise in the air, then dissolve in the water vapour in the clouds to form nitric acid, leading to acid rain.

Cracking Hydrocarbons

Cracking: The breaking down of long-chain alkanes into shorter, more useful alkanes and alkenes. (fuel) (plastic)

Cracking in the lab:

- The mineral wool holds the long-chain alkane at the end of the test tube.
- The tube is heated gently at the alkane so it doesn't combust but turns into a gas.
- The test tube is heated strongly at the catalyst so it can react with alkane gas → The reaction happens here.
- Pottery fragments before the catalyst and cracks the alkane.
- Stop the heating and collect the bung to prevent suckback.

The oil refinery uses the same process for cracking. Long chain heat the hydrocarbon until it vapourises, then pass the vapour over a hot catalyst. Catalytic cracking when a catalyst is used.

EQUATIONS:

Alkenes 

- Alkenes, also known as unsaturated hydrocarbons, only contain carbon and hydrogen.
- Alkenes are compounds that contain at least one C=C bond.

- Simplest alkene = ethene
→ There's no 'methene', only 1 carbon atom cannot have a double bond. 

- EXAMPLE - Propene
- Molecular formula - C₃H₆
- Displayed formula:

- Structural formula - CH₂= CHCH₃

Functional group: C=C

- General formula for alkenes = C_nH_2n
- Alkenes are another example of a homologous series.
- As you go down the series, the melting point and boiling point increase as there are stronger weak intermolecular series in between molecules. The molecules get bigger.
(as chain length ↑)

COMPARING COMBUSTION

Testing for Alkenes 

- We can use the difference in reactivity to distinguish between alkanes and alkenes.

- METHOD
1. Set up 3 test tubes—1 with 5cm³ cyclohexane, 1 with 5cm³ cyclohexene + 5cm³ of unknown c_n.
2. Put bungs on test tubes.
3. Add bromine water drop by drop to each test tube and put the bung back on. 
4. Shake from side to side and record observations in a table.

- RESULTS
- Cyclohexane (i.e., alkanes) stayed orange.
- Cyclohexene (i.e., alkenes) went from orange → colourless.

Alkenes and Bromine

- These are addition reactions.

Alkanes and Bromine 

- Alkanes are extremely unreactive and won't react with bromine at room temperature, but they will react with bromine when exposed to UV light.
- A substitution reaction occurs (in the presence of UV light) as a bromine atom takes the place of a hydrogen atom.
→ If there's enough bromine, all 4 hydrogen atoms in methane will be replaced one by one.

Isomers 

Structural isomers - Molecules with the same molecular formula but different structural formulas.

- EXAMPLES
- Butane + Methylpropane
  One carbon coming off.

2. But-1-ene + But-2-ene
Numbers tell us position.

Naming Alkanes 

STEPS
1. Find the longest chain—this is the root name (e.g., methane).
2. Identify any branches and count carbons and end in -yl (e.g., methyl)
3. Number the longest chain so branches are attached to the lowest number carbon.
4. Put branches plus their numbers in alphabetical order.

Note: Place a comma(s) between the numbers and a hyphen between them and the letter.

EXAMPLES

Alcohols 

- Alcohols are another homologous series.
→ All contain alcohol/hydroxyl groups.
→ This OH group, a functional group, means all alcohols react in a similar way.
- METHANOL - CH₃OH

CH₃OH

General formula: 
C_nH_2n+1 + OH

- ETHANOL - C₂H₅OH

CH₃CH₂OH

- PROPANOL - C₃H₇OH

CH₃CH₂CH₂OH

OR

CH₃CH(OH) CH₃

- BUTANOL - C₄H₉OH

CH₃CH₂CH₂CH₂OH

OR (one more option)

CH₃CH(OH)CH₂CH₃

 

Ethanol 

- Ethanol is part of a homologous series: Alcohols

USES OF ETHANOL
- As a solvent: Dissolve things in it to make solutions for chemical reactions and as a disinfectant.
- As a fuel, ethanol is highly flammable.
→ C₂H₅OH + 3O₂ → 2CO2 + 3H2O 
 - As an alcoholic drink.

MAKING ETHANOL—FERMENTATION

- Ethanol can be produced by the fermentation of sugar. 
- The raw materials are mixed with water and yeast. 
- Yeast contains zymase (an enzyme), which are biological catalysts.
- The sugars react to form ethanol + CO₂.

3 conditions for fermentation:
1. Yeast
2. ≥ 30°C (normal pressure)
3. Anaerobic conditions: Yeast respires anaerobically.

- Raw (plant) material contains glucose.
           - e.g., grapes/maize
- Fermentation cannot produce solutions containing ≥ 15% ethanol: The higher concentration becomes toxic to the yeast—it dies.
- Fermentation = batch process + slower reaction rate

EXPERIMENT

- The limewater turns cloudy as CO₂ is formed.
- Ethanol is impure, so separate it by filtering and then distilling. (from yeast)

- C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂
Glucose → Ethanol + Carbon Dioxide

- In the production of ethanol, it's important to allow CO₂ to escape and prevent air from entering the reaction vessel.
→ Is often achieved using an airlock.
- If the product is wine/beer, the yeast will be removed after fermentation, and the drink is bottled at this stage.

- To make spirits, ethanol conc. is higher, or to get pure ethanol—for solvent/fuel, ethanol is separated from the reaction mixture by filtering and then distilling.
- The CO₂ is allowed to escape to prevent pressure build-up.

Hydration of Ethene

Raw material—from crude oil → Ethene is obtained by cracking and fractional distillation.
 
→ C₂H₅OH

CONDITIONS

- 300°C 
- 60-70 atm → high pressure
- H₃PO₄ (phosphoric acid-concentrated) → as a catalyst
- Is distilled out after.
- pure(r) ethand made.
- The process is continuous and has a faster reaction rate.

COMPARISON

Carboxylic Acids 

- Another homologous series
→ functional group = COOH
- All carboxylic acids end their name with '-oic acid'. 

MEATHANOIC ACID

→ HCOOH

ETHANOIC ACID
→ CH₃COOH

PROPANOIC ACID
→ CH₃CH₂COOH

BUTANOIC ACID
→ CH₃CH₂CH₂COOH

Making Carboxylic Acids

- The process involves the oxidation of ethane, which includes all alcohols.

- If left standing in air, ethanol will slowly oxidise with the help of bacteria, forming ethanoic acid.
→ Microbial oxidation 
→ Sour taste (vinegar-like); why wine left in open air goes sour. 

EQUATION

-Warming ethanol with an oxidising agent, such as an acidified potassium dichromate solution, speeds up the oxidation process to produce ethanoic acid.
oxidising agent symbol: k₂cr₂O₇ → [o]

Ethanol + Potassium dichromate → Ethanoic acid + Water 

- Colour change when acidified k₂cr₂O₇ solution is used to oxidise ethanol: Orange to green 
- Conc. H₂SO₄ Sulphuric acid serves as a catalyst and is also present.

Chemical Properties

Carboxylic acids = Weak acids

- CH₃COOH partially ionises, so there's a lower conc. of H⁺ ions → weaker acid.

Weak vs. Strong Acids

- e.g., HCL vs. H⁺CL^-
→ HCl completely ionises, so there's a higher concentration of H⁺ ions; it's a strong acid.
- This means carboxylic acid reactions will be less vigorous compared to strong acids like HCl + H₂SO₄.

ETHANOIC ACID

- Appearance/Smell: Colourless + Vinegar smell 
- Turns orange/red with UI paper. 
- Add magnesium ribbon; the solid would disappear and the effervescence would increase.

ACIDS RECAP

- Acid + Metal → Salt + Hydrogen
- Acid + Metal oxide → Salt + Water
- Acid + Metal hydroxide → Salt + Water
- Acid + Metal carbonate → Salt + Water + Carbon dioxide
- Ethanoic acid + Sodium hydroxide → Sodium ethanoate + Water

Carboxylate Salts 

- Methanoic acid = Methanoate
- Ethanoic acid = Ethanoate
- Propanoic acid = Propanoate
- Butanoic acid = Butanoate

E.g., Carboxylate salt = Sodium butanoate
CH₃ CH₂CH₂COONa

EXAMPLES

1. Ethanoic acid + Sodium carbonate reaction:
- Ethanoic acid + Sodium carbonate → Sodium ethanoate + Water + Carbon dioxide
- CH₃COOH + Na₂CO₃ → CH₃COONa + H₂O + CO₂

2. Propanoic acid + Lithium reaction:
- Propanoic acid + Lithium → Lithium propanoate + Hydrogen 
- 2CH₃CH₂COOH + Li → 2CH₃CH₂COOL + H₂

3. Ethanoic acid + Calcium reaction:
- Ethanoic acid + Calcium → Calcium ethanoate + Hydrogen 
- 2CH₃COOH + Ca → (CH₃COO)₂Ca + H₂

Esters

- Another type of homologous series.

USES

- Volatile and sweet-smelling ingredients are often used in perfumes.
→ Easily turn into vapour: Distinctive smells can easily travel through the air to our noses.
- As artificial flavours in food.

HOW THEY ARE MADE?

- Add an alcohol to a carboxylic acid.
- Reaction catalysed by sulphuric acid.
- Reaction is reversible =

∴ For example, above: Ethyl ethanoate

Continued 

- When adding an alcohol + Carboxylic acid, this reaction = condensation reaction (:: water is made).

EXAMPLES
1. Propanol + Methanoic acid
→ Propyl methanoate

2. Butanoic acid + Ethanol
→ Ethyl butanoate

- Pentanoic acid + Pentanol
→ Pentyl pentanoate

Word equation:
Ethanoic acid + Propanol Propyl ethanoate + Water

Preparing a Sample of an Ester 

PROCEDURE
1. Add 10 drops of glacial ethanoic acid to the test tube containing concentrated H₂SO₄ acid. This is corrosive, so wear gloves and exercise caution.
2. Add 10 drops of methanol, ethanol, or but-1-ol. 
3. Add ≈ 50 cm³ of hot water from the kettle into 100 cm³ beaker.
4. Place the test tube in hot water and leave it for around 1 minute.
5. Add ≈ 20 cm³ sodium carbonate to another 100 cm³ beaker.
6. Carefully remove the test tube from the hot water bath and pour the contents into a beaker with Na₂CO₃.
→ Mixture effervesces as excess acids neutralise; you might also see ester floating on top as a separate layer.
7. Carefully smell the beaker's contents, using techniques such as wafting.

Polymers 

- POLYMER: Several monomers combine to form long-chain molecules.
- MONOMER: Molecule used to make a polymer.
- POLYMERISATION: The process in which numerous monomers react to form a polymer.

- The polymerisation of alkenes = Addition polymerisation
- Polymers are named after the monomers they're formed from.

NAMING POLYMERS EXAMPLES
- Propene → poly(propene) 
- Chloroethene → poly(chloroethene) 
- Ethanol → poly(ethanol)

DRAWING ADDITION POLYMERS

1. Propene:

2. Tetrafluoroethene:

3. Chloroethene:

- For example, we cannot write an exact formula for poly(ethene), so we instead display the polymer's repeating unit.
- The reaction occurs when the double bonds in ethene break, enabling molecules to stack on top of each other, a process known as addition polymerisation.

Condensation Polymerisation 

- In addition polymerisation, there's only one monomer; double bonds break, allowing monomer molecules to join together.
- However, in condensation polymerisation, different monomers join, resulting in the loss of a small molecule. 

- In condensation polymerisation, two monomers used are: 
1. Dicarboxylic acids (2-COOH groups at the end of each molecule).
2. Diols—2 alcohol (OH) groups at the end of each molecule.

- Polyester is made.
- Double bonds, such as those of oxygen, do not break.

Polyesters

- Polyesters are used for clothing.
→ Strong and resistant to most chemicals.

- The reaction of 100s of ethanediol and ethanedioic acid molecules needed to make a single fibre of polyester can be represented by this equation (also shown on the side before):

- Polyesters are very resistant to chemical and microbial attack; they're environmentally hazardous as they're difficult to biodegrade. 
→ Chemists have designed biopolyesters.
- Biopolyesters are polyesters that, on prolonged contact with oxygen, break down into CO₂ + H₂O.
→ Residue from the polyester is non-toxic and can be subject to the natural decay process.