7. Organic Chemistry

What are Alkanes?

Saturated Hydrocarbons

General formula CnH2n+2

What do hydrocarbons contain?

Only carbon and Hydrogen

What does saturated mean?

Contains only single bonds

What are the first four alkanes?

Methane, Ethane, Propane, Butane (Monkeys Eat Peanut Butter)

How can alkane molecules be represented?

1. Molecular Formula e.g Methane CH4

2. Displayed (structural) formula (picture)

Uses of fractions and trends

Small molecules - Low bpt, very volatile, low viscocity, flammable

Large molecules - high bpt, not very volatile, high viscocity, ignites poorly

Use of gas (LPG)

Fuel for domestic heating and cooking

Use for petrol

Fuel for cars

Use for kerosene

Fuel for aircraft

Use for diesel

Fuel for some cars and trains

Use for fuel oil

Fuel for ships and power stations

Use for bitumen

Material for roads and roofs

What is a homologous series?

Same:

General formula

Functional groups

Similar Chem. properties

What is crude oil?

Mixture of compounds; fossil fuel consisting of the remains of ancient biomass

Finite resource

What does incomplete/complete combustion of Hydrocarbons produce?

Complete combustion produces CO2 + H2O (carbon and hydrogen atoms are completely oxidised)

Incomplete combustion produces C or CO + H2O

Is combustion of hydrocarbons endo or exo

Exothermic and occurs when hydrocarbons are reacted with oxygen

How can we detect the products of complete combustion of hydrocarbon fuels/ alkanes?

Using this apparatus

Limewater turns cloudy - CO2 produced

Anydrous copper sulphate turns from white to blue & Cobalt chloride paper turns from blue to pink - H2O produced by fuel burning

Physical properties of alkanes - states

-First few = gases, then liquids, then solids

Physical properties of alkanes - BPTs and Vicsocity

increase as molecules get bigger

Physical properties of alkanes - tendency to change

Decreases as molecules get bigger

Physical properties of alkanes - reactivity

Poor reactivity

Fractional distillation of crude oil

-Heat the crude oil to vaporise most of the hydrocarbons

-Vapours rise up the column

-Column is cooler at the top

-Most vapours cool and condense at different heights due to different bpts

-V. Low boiling fractions removed as gases

-V. High boiling fractions removed as gases

What is cracking?

When large hydrocarbons are thermally broken down into smaller and useful molecules

Breaking down long alkane molecules into smaller alkanes and also alkenes

What type of reaction is cracking?

Thermal decomposition (evidence: one reactant forms two or more products)

What are the conditions for cracking?

Reactant heated to vapor

Passed over a hot catalyst (catalytic cracking) or heated to vapour, mixed with steam and heated to high temperatures (steam cracking)

How are the products of cracking used?

Products = Alkanes and Alkenes

Used as polymers

used as starting materials for synthesis

some products are useful as fuels since they have shorter chains than alkanes you started with = more flammable = better fuel

What is an alkene?

Unsaturated hydrocarbon

Contains a C=C bond

General formula = CnH2n

What is the test for alkenes?

Add bromine water

Colour change occurs from orange to colourless

Describe combustion of alkenes

burn with smoky flames due to incomplete combustion

Why does crude oil have limited uses?

It is a mixture of many different alkane hydrocarbons

Contains so many substances

How is crude oil formed?

Plankton buried and compressed in mud

Over millions of years

Under high temp and pressure

How do we make crude oil more useful?

It is separated into fractions (groups of hydrocarbon molecules of similar size and bpts)

Each fraction has a range of bpts because they contain a range of molecules

Seperated by fractional distillation

Why do bpts increase?

Molecules are larger

More energy needed to break

Stronger intermolecular forces

Why are fractions with smaller molecules (petrol, kerosene) good fuels?

All very flammable

Liquid flows easily

Why are fractions with big molecules (bitumen) bad fuels?

Very viscous (don’t flow well)

Not flammable

How is CO2 produced when burning fuels and what are it’s effects?

Complete combustion

Global Warming

How is CO produced when burning fuels and what are it’s effects?

Incomplete Combustion

Toxic / Killer - Stops red blood cells transporting oxygen

How is C produced when burning fuels and what are it’s effects?

Incomplete combustion

Global Dimming, Asthma/Lungs, Global Cooling

How is SO2 produced when burning fuels and what are it’s effects?

S impurities burn in oxygen

Acid Rain

How is NOx produced when burning fuels and what are it’s effects?

N2 + O2 increase in temp

Acid Rain

Conditions needed for industrial cat. cracking

High temp (to give molecules activation energy)

Catalyst (speeds up reaction without being used up)

Absence of air (prevent hydrocarbons burning in O2)

How to carry out industrial cat. cracking

Heat the alkane to vaporise it

And pass vapours over a hot catalyst (aluminium oxide)

Conditions for industrial steam cracking

High temp

Steam

Absence of air

How to carry out industrial steam cracking

Heat the alkane to vaporise it

And mix vapours with steam

Why is cracking done?

-meet demand for good fuels

-make polymers and plastics from alkenes

Cracking Equations

-Same no. of carbons and hydrogens on each side (same as any eqtn.)
-Bigger molecule to 2 smaller molecules

How + why are the products of cracking seperated?

seperated by fractional distillation because they have different bpts

Advantages of cracking

Provides fuels: to meet high demand

Makes alkenes: used to make polymers

Disadvantages of cracking

Uses fossil fuels to provide energy for cracking: they are non-renewable

Burning fuels: CO2 emissions global warming, SO2 + NOx emissions acid rain

Chemicals for cracking come from crude oil: non-renewable

Products of cracking require f.d which uses non-renewable fossil fuels

What are alkenes?

Unsaturated hydrocarbons (contains a double bond)

What is the general formula for alkenes?

CnH2n

Why is there no ‘methene’?

2 carbons are needed to make a double bond

‘meth’ means 1 C

Why are alkenes more reactive than alkanes?

They have a double bond which breaks open

What is alkenes functional group?

C=C

What is hydrogenation?

When alkenes react with hydrogen to form alkanes

Double bond breaks

What is halogenation?

When alkenes react with halogens to form alkenes

Double bond breaks

How do alkenes form alcohols?

React with steam (H2O)

Why are alkene reactions addition reactions?

Double bond breaks

Other atoms add on

What are polymers?

Very long molecules formed by combining many small molecules

What are addition polymers?

Formed from many alkene molecules (or alkene ‘type’ molecules)

What does ethene form when it’s an addition polymer?

Polyethene:

C=C breaks

Many molecules combine

To form a very long chain

What is needed in a repeat unit?

Bracket

^That cuts through lines

‘n’ to show repeating

What are polymers and plastics made from?

Alkenes

First four alkenes

ethene, propene, butene, pentene

How do alkenes react with oxygen?

In the same way as other hydrocarbons: in combustion reactions

However, they tend to burn in air with smoky flames because of incomplete combustion (carbon or carbon monoxide formed (CO))

Alkenes reaction with hydrogen, water and the halogens

Reaction by the addition of atoms across the carbon-carbon double bond so that double bond becomes single carbon-carbon bond

What happens in every alkene reaction with hydrogen, water and halogens?

every reaction works the same for all alkenes

C=C bond breaks to form C-C bond

Compound added splits into two groups and two groups added to 2 carbons in the C=C bond (each group added to either carbon)

e.g H2 Splits into 2 H’s, H2O splits into a H and an OH, Br2 splits into 2 Brs

Alcohol’s functional group

-OH

What are the first 4 members of the alcohol series?

Methanol (CH3OH)

Ethanol (C25OH)
Propanol (C3H7OH)

Butanol (C4H9OH)

Reactions of methanol, ethanol, propanol and butanol (alcohols)

-Burn in air: produces CO2 and H2O
-Dissolve in water: forms neutral solution (PH = 7)

-React with sodium to produce hydrogen and a salt (e.g C2H5ONa - H given off, Na added)

-React with oxidising agents to form carboxylic acids

Uses of methanol

Chemical feedstock, in anti freeze, to make biodiesel

Uses of ethanol

Main alcohol in alcoholic drinks, used as solvent and fuel

Uses of all 4 (methanol, ethanol, propanol, butanol)

Can be used as fuels

How to produce ethanol

Can be produced by fermentation of sugar with yeast, using renewable sources

Conditions of producing ethanol

about 35 degrees

anaerobic (without oxygen)

yeast enzyme catalyst

Equation of producing ethanol (written)

Sugar → Ethanol + Carbon Dioxide

What is ethanoic acid?

Member of the carboxylic acids

What is the functional group of carboxylic acids?

-COOH

First four members of carboxylic acids

Methanoic Acid (CHOOH)

Ethanoic Acid (CH3COOH)

Propanoic Acid (C2H5COOH)

Butanoic Acid (C3H7COOH)

Reactions of methanoic acid, ethanoic acid, propanoic acid, butanoic acid

Dissolve in water: produce acidic solutions (pH under 7)

React with metal carbonates: produce carbon dioxide (turns limewater cloudy), a salt and a water

Reacts with alcohols in presence of an acid catalyst: produce esters

Ester we need to know name of

Ethyl ethanoate

Why are carboxylic acids weak acids?

They do not ionise completely in solutions so do not release many H+ ions

This means they have higher pH (less acidic) than solutions of strong acids of the same conc.

What kind of polymers can alkenes be used to make?

Poly(ethene) and poly(propene) by addition polymerisation

What happens in addition polymerisation?

Many small molecules (monomers) join together to create very large molecules (polymers)

Example of addition polymerisation

Repeat unit has same atoms as monomer because no other molecule is formed in the reaction

What does condensation polymerisation involve?

Monomers with two functional groups

What happens in reaction of condensation polymerisation?

When monomers react, they join together and usually lose small molecules (water)

So reactions are called condensation reactions

How are simplest polymers produced? (condensation polymerisation)

From two different monomers with two of the same functional groups on each monomer

Example of condensation polymerisation

e.g polyester: 1 monomer with 2 carboxylic acids func groups

1 monomer with 2 alcohol func groups

How many functional groups do amino acids have?

Two different func. groups in a molecule (amine group and carboxylic acid group)

How do amino acids react?

By condensation polymerisation to produce polypeptides

How can different amino acids be combined in the same chain?

To produce proteins

What is DNA?

A large molecule essential for life - encodes genetic instructions for development and functioning of living organisms and viruses

What are most DNA molecules made up of?

two polymer chains made from four different monomers called nucleotides in the form of a doube helix

Other than DNA, what are other naturally occuring polymers important for life?

Proteins (monomer = amino acid)
Starch (monomer = glucose)

Cellulose (monomer = glucose)

What is a monomer?

Molecule that can react with other monomer molecules to form a larger polymer chain