GCSE Chemistry- Organic Chemistry

What is meant by hydrocarbons?

What is meant by hydrocarbons?

Any compound that is formed from carbon and hydrogen only

First four alkanes

Methane CH4 Ethane C2H6 Propane C3H8 Butane C4H10

Homologous series

A homologous series is a group of organic compounds that have similar chemical properties, due to them having the same functional group, same general formula and differ by CH2.

Alkanes general formula

Alkanes

• Saturated compounds, meaning every carbon atom has 4 single covalent bonds

• Homologous series of molecules that contain only hydrogen and carbon atoms

How many hydrogen atoms are there in an alkane with 5 carbon atoms?

12 hydrogen atoms

Isomers

Molecules that have the same molecular formula, but different structural formulas. Made of the same atoms, but the atoms are arranged differently.

eg. pentane and methylbutane both have the formula C5H12 but the atoms are arranged differently

As the chain length (number of carbon atoms) of alkanes increases, they become:

• Boiling point/Melting point increases with chain length (first four alkanes are gases at room temp, longer alkanes with more than 4 carbons are liquids at room temp and some are even solid)

• Longer alkanes are less volatile as they have a higher bp so don't evaporate easily

• Longer alkanes are more viscous (thick, sticky)

• Longer alkanes are less flammable

Complete combustion

hydrocarbon + oxygen --> carbon dioxide + water

• Carbon and hydrogen in the fuels are oxidised (exothermic as it releases energy)

Balanced equation for the combustion of propane

C3H8 + 5O2 --> 3CO2 + 4H2O

Balanced equation for the combustion of nonane

C9H20 + 14O2 --> 9CO2 + 10H2O

What is meant by crude oil?

Crude oil is a mixture of many different compounds. Most of the compounds are hydrocarbons, which are molecules made up of hydrogen and carbon atoms only. Crude oil is a finite resource found in rocks.

How crude oil was made?

1. Crude oil is formed from the remains of dead plants and animals, particularly plankton.

2. These organic remains were covered by mud and sand, and buried in the earth.

3. Over millions of years, these organic remains were compressed under a lot of heat and pressure.

4. The heat and pressure chemically changed the organic remains into crude oil.

How to separate the hydrocarbons in crude oil?

May be separated into fractions, each of which contains molecules with a similar number of carbon atoms, by fractional distillation.

How fractional distillation of crude oil works?

1. Crude oil is a mixture of hydrocarbons with different boiling points.

2. The first step is to heat the crude oil to a very high temperature so that all of the compounds are evaporated from liquid to gas.

3. The hot gaseous hydrocarbons then rise up the fractionating column (because hot gas rises).

4. As they rise, they cool down, because the top of the column is cooler than the bottom.

5. The hydrocarbons will condense when they become cooler than their boiling point, and the liquid hydrocarbons then collect in trays and drain out.

6. The longer chain hydrocarbons condense at the bottom of the fractionating column because they have high boiling points.

7. Meanwhile the shorter chain hydrocarbons condense at the top of the column because they have much lower boiling points.

Feedstocks and petrochemicals

Feedstock: is a raw material used to provide reactants for an industrial reaction.

Petrochemical: is a substance made from crude oil, via chemical reactions.

• fractions can be processed to produce fuels and feedstock for the petrochemical industry

Different hydrocarbons in crude oil are all feedstocks, but the useful things we then make from those hydrocarbons (polymers, solvents, lubricants, detergents etc.), are all petrochemicals.

What is produced by the petrochemical industry?

Solvents, lubricants, polymers and detergents

Order of hydrocarbons in crude oil

LPG (liquefied petroleum gases)- short hydrocarbon so stays as a gas contains mainly propane and butane used as a fuel Petrol- cars Kerosine - aeroplane fuels Diesel - cars/lorry's Heavy fuel oil - can be separated further used for heating oil, fuel oil or lubricating oil (ships) Bitumen - surface roads + roofing

• Diesel, Kerosine, Petrol and LPG are the most flammable and tend to make the best fuels

• Bitumen and Heavy Fuel Oil are either used for something else or can be broken down into smaller hydrocarbons by cracking.

Why is carbon able to form a vast array of compounds?

The vast array of natural and synthetic carbon compounds occur due to the ability of carbon atoms to form families of similar compounds.

What is meant by cracking?

Hydrocarbons can be broken down (cracked) to produce smaller, more useful molecules. A thermal decomposition reaction as it involves using heat to break something apart.

Cracking can be done by various methods including:

• catalytic cracking and steam cracking.

Catalyctic cracking

1. First heat the hydrocarbon molecules to around 470 - 550°C to vaporise them

2. The vapours then pass over a hot powdered catalyst of aluminium oxide. This process breaks covalent bonds in the molecules as they come into contact with the surface of the catalyst, causing thermal decomposition reactions

3. This breaks the long chain alkanes into a small chain alkane and an alkene

Hydrogen and a higher proportion of alkenes are formed at higher temperatures and higher pressure

Steam cracking

1. vaporise hydrocarbon

2. mix with steam

3. heat to a very high temperature

Process is carried out at slightly higher temperatures and produces more ring structures and unsaturated compounds The vaporised hydrocarbons are mixed with steam and heated to a high temperature which induces cracking.

Describe in general terms the conditions used for stream cracking?

• higher temperature over 800 degrees celsius

• no catalyst

Products of cracking

Shorter chain alkanes and alkenes Longer Alkane --> Shorter Alkane + Alkene

• alkenes can be used to produce polymers and used as starting materials to produce other chemicals

Why are alkenes produced in cracking?

• When a long chain alkane is cracked, there aren't enough hydrogen atoms to make two alkanes.

• Hence, cracking will always produce one alkane and one alkene. (Alkenes are hydrocarbons with a double bond between two carbon atoms).

An unknown alkane was cracked to produce propene (C3H6) and pentane (C5H12).

? ➔ C3H6 + C5H12

Octane C8H18

(number of hydrogens and carbons have to be equal on both sides)

C9H20 ➔ C2H4 + C?H?

Nonane (C9H20) is cracked to produce ethene (C2H4) and one other product. What is the other product?

Heptane C7H16

Alkanes vs Alkenes

Alkenes are...

• also hydrocarbons and also an example of a homologous series

• unsaturated as they have a double bond

• more reactive than alkanes and react with bromine water, which is used as a test for alkenes

• can be added together to make polymers as double bonds can break to form 2 or more bonds so they can bonds to adjacent molecules

Test for alkenes

bromine water orange to colourless

Explain how modern life depends on the uses of hydrocarbons.

Many useful materials on which modern life depends are produced by the petrochemical industry, such as solvents, lubricants, polymers, detergent.

Demand for fuels with smaller molecules as that is what most appliances, cars run on so cracking is important for daily life.

Alkenes

Are hydrocarbons with a double carbon-carbon bond.

• Molecules are unsaturated because they contain two fewer hydrogen atoms than the alkane with the same number of carbon atoms

Alkenes general formula

First four alkenes

Ethene C2H4 Propene C3H6 Butene C4H8 Pentene C5H10

Addition reaction between an alkene and hydrogen

Reacting an alkene with hydrogen gas, and a catalyst, will produce an alkane. C3H6 + H2 ➔ C3H8

• Double bond is broken (saturated) and there is an addition of 2 hydrogens

Addition reaction between an alkene and water

• Requires a catalyst and high temperatures (300C) so the water is in the form of water vapour. C2H4 + H2O ➔ C2H5OH\

• Have to separate the ethanol from the unreacted water and unreacted ethene.

how to separate ethanol and water

fractional distillation:

1. Take the mixture of ethanol and water and placing it in a round bottom heating flask, heat it up with a bunsen burner.

2. Ethanol will boil first as it has a slightly lower bp than water.

3. It will evaporate up through the fractionating column and then condense into a separate beaker. Whereas our water will remain in the heating flask.

Addition reaction between an alkene and halogen

• No catalyst required and will produce a halogenoalkane. C2H4 + Br2 ➔ C2H4Br2 (Dibromoethane) Ethene + iodine → diiodoethane Ethene + chlorine → dichloroethane

If bromine water is used it will turn the solution colourless as

C4H8 + Br2 ➔ ?

Butene (C4H8) can react with Bromine (Br2) to produce a halogenoalkane.

What halogenoalkane is produced in the reaction?

Dibromobutane C4H8Br2

Addition polymerisation

Formation of a very long molecular chain, by repeated addition reactions of many unsaturated alkene molecules (monomers).

Alkenes can be used to make polymers such as poly(ethene) and poly(propene) by addition polymerisation. In addition polymerisation reactions, many small molecules (monomers) join together to form very large molecules (polymers).

How to draw addition polymerisation

poly(alkene)

• number, monomer (catalyst) (pressure) --> repeating unit, number

• Draw the bonds of the monomer facing up and down rather than at angles

• On the repeating unit, you need to draw empty bonds pointing out to the left and right through the brackets

• Have the 'n' to signify a large number of monomers and repeating units.

How to name polymers?

Take the alkene name Put brackets around it Add 'poly' to the front of the name, before the first bracket.

eg. ethene would become poly(ethene) chloroethene would become poly(chloroethene)

Polymer meaning

a large molecule that is made from multiple smaller monomers.

Which of these could not be used as a monomer in addition polymerisation? Ethene Butane Butene Propene

Butane is an alkane and doesn't have any double bonds, which are required for addition polymerisation.

Alcohol

A homologous series, with a functional group of OH.

• Replace the final 'e' with an 'ol' when naming (ethane --> ethanol)

Alcohol general formula

first four alcohols in the homologous series

Methanol - CH3OH Ethanol - C2H5OH Propanol - C3H7OH Butanol - C4H9OH

First four alcohols are all flammable, soluble and can be oxidised to form carboxylic acids.

describe what happens when any of the first four alcohols react with sodium

If a small piece of sodium is dropped into ethanol, bubbles of hydrogen gas are produced and the liquid contains sodium ethoxide (salt).

describe what happens when any of the first four alcohols: burn in air

Flammable: can undergo complete combustion in air. They react with oxygen to form carbon dioxide and water. alcohol + oxygen --> carbon dioxide + water

describe what happens when any of the first four alcohols: are added to water

Soluble: dissolve in water to form a solution. As alcohol isn't acidic or alkaline their solutions will have a neutral pH.

describe what happens when any of the first four alcohols: react with an oxidising agent

Carboxylic Acids: forms when you oxidise an alcohol and has a functional group of -COOH.

Uses of alcohol

• Use as fuels as it is flammable and undergoes combustion, it is able to release lots of energy

• Use as solvents in industry (often instead of water) as alcohols can dissolve things that water can't particularly hydrocarbons and lipid compounds (fats and oils)

What is the displayed formula of butanol?

What is ethanol and what is its uses?

Ethanol is an alcohol with the formula CH3CH2OH

• It is used as a chemical feedstock to produce other organic compounds

• It can be burned to be used as biofuel

• It can be used to make alcoholic drinks such as beer and wine

Ethanol can be produced from steam

Type of reaction: Addition reaction because the water molecule is being added to the ethene molecule.

Conditions: High temperature (300 °C), high pressure (60-70 atm), phosphoric acid catalyst.

Advantages: Ethene is cheap and the reaction itself is cheap and efficient.

Disadvantages: Ethene is made from crude oil which is a non-renewable resource, so if it starts to run out it will become expensive.

Ethanol can be produced by fermentation

Fermentation is the anaerobic respiration of sugars by yeast cells to produce ethanol and carbon dioxide.

glucose --> ethanol + carbon dioxide Type of reaction: Anaerobic respiration (respiration without oxygen).

Conditions: Carried out in fermentation tanks. Requires yeast cells which have naturally occurring enzymes to catalyse the reaction. Temperatures of 30-40 °C (this is optimum temperature for the enzymes). Must be anaerobic conditions (no oxygen), so that the ethanol isn't oxidised to ethanoic acid.

Advantages: The sugar/glucose used is a renewable resource so can't run out. Yeast are easy to grow.

Disadvantages: The process can be relatively slow. The ethanol produced isn't pure so must be distilled by fractional distillation.

Carboxylic Acid

• Are a homologous series and are basically alkane chains.

• Have a functional group -COOH

• Names end in 'anoic acid'

Carboxylic Acid general formula

First four members of a homologous series of carboxylic acids

Methanoic acid- HCOOH Ethanoic acid- CH3COOH Propanoic acid- C2H5COOH Butanoic acid- C3H7COOH

What type of acids are carboxylic acids?

Weak acids, meaning they don't fully ionise completely in water.

• Ionisation equation has an equilibrium arrow between the full acid on left and the ionised version on the right

• Negative ions they firm on the right have names that end in 'anoate' eg. C2H5COOH --> <-- C2H5COO- + H+

Carboxylic acids partially dissociate in water to form a negative ion and a hydrogen ion. The negative ion has a name ending with 'anoate ion'. Butanoic acid will ionise into a...

butanoate ion and a hydrogen ion

describe what happens when any of the first four carboxylic acids: react with carbonates

carboxylic acid + metal carbonate --> salt + water + carbon dioxide

describe what happens when any of the first four carboxylic acids: dissolve in water

dissolve in water to form acidic solutions with pH values less than 7

describe what happens when any of the first four carboxylic acids: react with alcohols

Carboxylic acids can react with alcohols to form esters. Esterification reaction, involves the removal of the acidic hydrogen from the carboxylic acid and its replacement with an alcohol molecule.

explain why carboxylic acids are weak acids in terms of ionisation and pH

• Carboxylic acids are weak acids because they only partially ionise in solution.

• Their solutions do not contain many hydrogen ions compared to a solution of a strong acid at the same concentration.

• A weak acid's pH will be higher than a strong acid's pH at the same concentration.

Carboxylic acids react just like any other acid. Therefore, they have the same acid / base reactions as other acids:

1. Carboxylic acid + metal ➔ salt + hydrogen

2. Carboxylic acid + metal oxide ➔ salt + water

3. Carboxylic acid + metal hydroxide ➔ salt + water

4. Carboxylic acid + metal carbonate ➔ salt + water + carbon dioxide

how carboxylic acids are made

Carboxylic acids are made from oxidising an alcohol with an oxidising agent. alcohol --> (oxidising agent) carboxylic acid

Esters

• -COO functional group in the middle of the molecule

• Distinctive property is that they have pleasant smells (sweet or fruity)

• Are volatile, which means they evaporate easily

• Used in perfumes and food flavourings

How to make esters?

Made by reacting a carboxylic acid and an alcohol in the presence of an acid catalyst (such as sulfuric acid).

eg. ethanoic acid + ethanol --> ethyl ethanoate use an acid catalyst, normally concentrated sulfuric acid

When they combine...

• Carboxylic acid loses its -OH group

• Alcohol loses the -H from its OH group

• Together these 3 atoms form a water molecule, a by product of the reaction

Draw the structure of ethyl ethanoate

Condensation Polymerisation

Involves monomers with two functional groups. When these types of monomers react they join together, usually losing small molecules such as water, and so the reactions are called condensation reactions.

What does the coloured box represent in condensation polymerisation?

The rest of the molecule in simplified form

Polyesters

Polymers formed by linking together monomers that have carboxylic acid groups with those that have alcohol groups.

2 different monomers: dicarboxylic acid monomer & diol monomer In order to combine...

• Dicarboxylic acid has to give up its OH group (right)

• Diol gives up a H atom from its OH group (left) When these 3 atoms combine they form a water molecule

This leads the carbon on the right of the dicarboxylic acid to bond directly to this oxygen from the diol. This bond is the ester link. Two monomers combined is a dimer.

To show its a repeating unit you remove the OH from the dicarboxylic acid on the left and the diol removes the H on the right. Put empty bonds out to the sides.

As we've removed another OH and H another water molecule is formed. Add brackets at either end that cut through the bonds.

reult: dicarboxylic acid monomer + diol monomer --> condensation polymer (polyester in eg as there is an ester link) + water

Use the letter n in front of each reactant and at the end of the product to represent the number. Don't forget the water molecule (2nH2O)

What do molecules need to have in order to combine in condensation polymers?

1. Each of the monomers has to have at least 2 functional groups eg. Dicarboxylic has 2 carboxyl groups and Diol has 2 alkyl group

2. Two different functional groups overall eg. carboxyl and alcohol group

3. Small molecules given off in the process eg. water

To make a polyester condensation polymerisation, the monomers need to have enough carboxylic acid and alcohol functional groups to form a long continuous chain. This means that each monomer needs to have at least two functional groups.

Example of a condensation polymer

ethanedioic acid + ethanediol --> poly(ethyl ethanoate) + water

polyesters vs addition polymers

Polyesters:

• Generally biodegradable which means they can break down naturally because bacteria and other microorganisms can break down the ester links Addition Polymers:

• Generally aren't biodegradable so stay in the environment for a long time

Polypeptide

A polymer (chain) of many amino acids linked together by peptide bonds.

• When a polypeptide folds up or combines with other polypeptides we call it a protein because there are loads of different amino acids which can combine in many combinations

Amino Acid Structure

Carboxyl group, Amino group, R group at the bottom (changes depending on which amino acid it is, therefore makes each amino acid different). Joined together by a central carbon.

To form a polymer these 2 functional groups (carboxyl and amino) allow adjacent amino acids to join together through condensation reactions. Occurs when the OH from the carboxyl group and the H from the amino group react together producing water.

Carbon and nitrogen then bond together amide/peptide bond.

For repeat units you need to put n, draw the end bonds and brackets.

complete the equation for the condensation reaction between amino acids.

(-HNCH2CO-)n + nH2O

DNA

Is a large molecule essential for life. DNA encodes genetic instructions for the development and functioning of living organisms and viruses.

DNA Structure

Monomers are structures called nucleotides and all contain a small molecule called a base.

4 different bases:T, A, G, C and the rest of the nucelotide stay the same. 4 different types of nucleotides one for each of the four base.

By combining these nucleotides in different orders our cells can effectively make different codes, which we call genes.

• To keep these codes intact and prevent them from getting damaged. DNA is made of 2 polymer chains that are linked together, forms a double helix.

Carbohydrates

(refers to a number of different polymers and monomers) We derive energy from are all made of only carbon, oxygen and hydrogen.

• Polymers called 'polysaccharides' are starch, cellulose and glycogen.

• Monomers called 'monosaccharides' (sugars) include glucose and fructose By combining monomers (glucose) we can form polymers like (starch).

naturally occurring polymers important for life

starch, proteins, and cellulose