[26] Organic Chemistry

what are organic compounds?

All carbon-containing compounds (except CO, CO₂, and carbonates) are organic compounds.

Hydrocarbon

A compound containing only hydrogen and carbon atoms.

Alkane

A saturated hydrocarbon with only single C–C bonds.

Homologous Series

A group of compounds with similar chemical properties, the same general formula, and each member differs by a CH₂ group.

General Formula of Alkanes

CₙH₂ₙ₊₂

Isomers

Compounds with the same molecular formula but different displayed formulae.

Effect of Isomer Shape

Fewer surface contact points → weaker intermolecular forces; more surface points → stronger intermolecular forces.

Crude Oil

A mixture of hydrocarbons of different chain lengths.

Fractional Distillation of Crude Oil

Separates hydrocarbons by boiling point. Small molecules (top) have low boiling points; large molecules (bottom) have high boiling points.

order of fractional distillation of crude oil from lowest bp to highest bp

refinery gases
gasoline
kerosene
diesel
fuel oil
bitumen

Trends in Fractional Distillation (small to large molecules)

Boiling point increases; viscosity increases; flammability decreases; flame gets smokier; colour gets darker.

Small Alkanes

Low boiling points, runny, easy to ignite, burn with a clean flame.

Large Alkanes

High boiling points, viscous, hard to ignite, burn with a smoky flame.

Cracking

Long-chain alkanes are broken into shorter alkanes and alkenes by heating. It is a thermal decomposition reaction.

Purpose of Cracking

To produce more short-chain hydrocarbons (like petrol) that are in higher demand.

Alkenes

A homologous series of hydrocarbons with at least one double C=C bond (unsaturated).

Difference Between Alkanes and Alkenes

Alkanes have single bonds (saturated); alkenes have double bonds (unsaturated).

General Formula of Alkenes

CₙH₂ₙ

Test for Alkenes

Add bromine water — it changes from orange to colourless.

Test for Alkanes what is this called

Add bromine water — no colour change unless UV light is present which will be a substitution reaction

complete combustion for hydrocarbons

hydrocarbon + oxygen → carbon dioxide + water.

Incomplete Combustion equation

hydrocarbon + oxygen → carbon monoxide + water / carbon + water

Signs of Incomplete Combustion

Yellow, smoky flame and formation of soot or CO.

Methane formula

CH₄

Definition of Saturated

A molecule with only single carbon-carbon bonds

Definition of Unsaturated

A molecule that contains at least one double carbon bond.

what is a suitable catalyst for cracking

aluminium oxide

what is a suitable temp for cracking

600-700 degrees

what type of reaction is cracking

thermal decomposition

what happens in an addition reaction in an alkene

double carbon bond turns into a single carbon bond

what does the addition reaction of a hydrogen with an alkene require?

150 degrees and a nickel catalyst

what does the structural formulae of ethene after addition reaction with water

how are alkenes made

by cracking

what is a monomer

alkene molecules

disadvantage of addition polymers

do not biodegrade

features of alcohols

burn well with oxygen and in the lab, alcohols can be oxidised slowly by mild oxidising agents to form carboxylic acids

what is it called when you leave alcohols in the open air

microbial oxidation

what is an example of an oxidizing agent that can be used to make carboxylic acids (reflux) and what is the colour change

acidified potassium dichromate it stars as orange and turns green

2 ways to make ethanol

fermentation and hydration of ethene

conditions for making ethanol with hydration of ethene method

300 degrees celcius, 60-70 atmospheres pressure and phosphoric acid catalyst

what is the process of the hydration of ethene

passing steam and ethene over a heated phosphoric acid catalyst

process of fermentation to make ethanol

raw materials are mixed with water and yeast at just above room temp which contains enzymes

the sugars in the raw materials react with the enzymes to form ethanol and carbon dioxide, the carbon dioxide is allowed to escape but air is prevented from entering the reaction vessel to stop oxidation of ethanol to ethanoic acid

when the reaction is over the ethanol is separated from the reaction mixture by fractional distillation

conditions needed for fermentation to make ethanol

30-40 degrees celcius, presence of water, sugar as glucose, absence of oxygen for anaerobic respiration to avoid anaerobic respiration where ethanol is oxidised to become ethanoic acid

pros and cons of hydration of ethene to make ethanol

is continuous and fast, the process gets you pure ethene but it uses fossil fuels which is a finite source

pros and cons of fermentation to make ethanol

does not use fossil fuels it uses crops that can be used again but the ethanol made is not pure so we have do distilled it so it has many steps and fermentation is a slow process and not continuous

features of carboxylic acids

• weak acid so they do not dissociate fully in water meaning they only partially donate protons

• react with alcohols to form esters

carboxylic acid + metal → ?

carboxylic acid + carbonates→ ?

carboxylic acid + alkalis → ?

salt+ hydrogen

salt + water + carbon dioxide

salt + water (neutralization)

what are salts formed by ethanoic acid called

ethanoates

functional group of carboxylic acids

COOH

molecular formula for propanoic acid ethanoic acid and methanooc acid

propanoic acid → CH₃CH₂COOH

ethanoic acid → CH₃COOH

methanoic acid→ HCOOH

displayed formula of methanoic ethanoic and propanoic acid

What is addition polymerisation?

A reaction where alkene monomers join to make a polymer without producing any by-products.

Why are addition polymers non-reactive?

Because they contain strong C–C single bonds and no reactive double bond.

Why are addition polymers a disposal problem?

They are non-biodegradable and persist for hundreds of years.

Name two problems caused by incineration of addition polymers.

1) Releases toxic gases, 2) Contributes to air pollution.

What is condensation polymerisation?

A reaction where monomers with two functional groups join, forming a polymer and a small molecule usually water

What two types of molecules form polyesters?

A diol and a dicarboxylic acid.

What functional group is formed in polyesters?

Ester links (–COO–)

Are condensation polymers biodegradable?

Some are, because ester links can be broken down easily

uses of alkenes

Alkenes are used to make plastics because their carbon–carbon double bond is reactive, allowing them to undergo polymerization and form long, strong polymer chains.

uses of short chain alkanes

used as petrol because they have lower boiling points, highly flammable and release alot of energy when burnt