11. Organic Chemistry Flashcards
What is produced when alkanes combust in oxygen?
Carbon Dioxide + Water
Combustion of ethanol
The combustion of ethanol is a reaction with oxygen that produces carbon dioxide and water.
Fuels
A chemical substance that when reacted (often by burning) releases energy
Three main types of fuels
Coal
Natural gas
Petroleum (generic name used to describe crude oil/ other hydroxarbons derived from crude oil)
Petroleum
The mixture of hydrocarbons found naturally formed by the decay of marine organisms. Also known as crude oil.
Combustion of methane
methane + oxygen → carbon dioxide + water
CH4(g) + 2O2(g) → CO2(g) + 2H2O(l)
Natural gas
Fuel extracted from underground.
(Main constituent = Methane)
Contains a mixture of hydrocarbons and impurities such as water.
Therefore has to be refined to make suitable for home use.
Fractions
The components in petroleum obtained after separation through fractional distillation.
Petroleum - Fractional distillation
1) Petroleum is heated to a high temperature + pumped into the bottom of the distillation tower.
2) Fractions with molecules with small no. of carbon atoms (eg. gasoline) –> have relatively low boiling point –> evporate first + rise up the tower.
3) As they rise up the tower they condense bc it becomes cooler. (Condense at different points to fractions collected at different temperatures)
Fractions - List
Small molecules with low boiling points.
Refinery gas
Bottled gas
Petrol (Gasoline)
Chemical feedstock
Jet fuel, paraffin
Diesel fuels
Lubricating oils + waxes/polishes
Fuel for ships/factories/central heating
Bitumen for roads + roofing
Large molecules with high boiling points
What is gasoline used for, and what are its properties?
- Fuel used in cars
- Very volatile (Low chain length)
- Very low viscosity (flows very easily)
- 5–6 carbon atoms
As the number of carbon atoms in the hydrocarbon increases…
- The boiling point increases
- The viscosity increases
- The volatility decreases.
What is kerosene used for, and what are its properties?
- Jet fuel
- Volatile
- Low viscosity
- 10–15 carbon atoms
What is lubricating oil used for, and what are its properties?
- Lubricating machinery + base for polishes and waxes.
- Low volatility
- High viscosity (thick liquid that flows slowly)
- 25–40 carbon atoms
What is bitumen used for, and what are its properties?
- Used for laying tarmac on roads (construction of roads)
- Very low volatility
- High viscosity (flows extremely slowly)
- 40+ carbon atoms
What is the use of refinery gas?
Used as bottled gas for heating and cooking (eg. in bunsen burner)
What is the use of naptha?
Used as a base for manufacturing many other chemicals.
eg. solvents used by painter decorators.
What is diesel oil used for?
Used as a fuel for trucks in diesel engines.
What is fuel oil used for?
Used as a fuel for ships or heating homes.
Organic compound
A substance consisting of carbon and one or more other elements, joined together by covalent bonds.
These compounds contain a functional group.
Functional group
An atom of a group of atoms in an organic compound that gives rise to the particular chemical reactions of that compound.
Eg. OH in alcohol or COOH in carboxylic acids.
Functional group defines the homologous series of a compound.
Homologous series
A family of compounds that will have the same general formula and similar properties but differ by the number of carbon atoms.
They all contain the same functional group which gives them similar chemical properties.
Eg. C-C functional group = Alkanes
General formula
A chemical formula that shows the ratio of atoms of each element for all members of a homologous series.
eg. CnH2n+2 = alkanes
General formula vs Structural formula
Eg. Ethene
The general formula shows the ratio
Ethene = C2H4
The structural formula shows how the atoms in a molecule are ACTUALLY arranged.
Ethene = CH2CH2
Alkanes - General formula
Cn H2n+2
Alkenes - General formula
Cn H2n
Alcohols - General formula
Cn H2n+1 OH
Carboxylic acids - General formula
Cn H2n+1 COOH
(n = number of carbons - 1)
Meth
C
Eth
C2
Prop
C3
But
C4
Displayed formula
A diagram that shows the symbols of the atoms in a compound and the covalent bonds between them.
(organic compounds)
Saturated compounds
Compounds that contain only C–C single bonds between the carbon atoms.
(organic compounds)
eg. Alkanes
Unsaturated compounds
Compounds that contain C=C double bonds between carbon atoms.
(organic compounds)
Eg. Alkenes
How many bonds do carbon atoms form in organic compounds?
Four
Structural formula
The displayed formula of a compound showing how the atoms in a molecule are arranged.
‘Increasing’ the compound in the homogolous series
Add a -CH2- unit when going from one molecule to the next —> the carbon chain becomes longer.
- Causes a trend in the physical properties of a homologous series.
- The intermolecular forces between molecules increase in strength as the carbon chain gets longer.
–> Melting point + Boiling point + viscosity (thickness) íncreases + volatility decreases (how easily vapour is formed.
Structural isomers
Compounds with the same molecular formula, but different structural formulae.
eg. But-1-ene vs But-2-ene
Writing the structural formula of an isomer…
CH3CH(CH3)CH3
The CH3 group that ‘sticks up’ from on carbon atom, is written in brackets.
–ane
Alkane
-ene
Alkene
-ol
Alcohol
-oic acid
Carboxylic acids
Methane
CH4
Ethane
Structural formula
CH3CH3
Molecular fomrula
C2H6
Ethene
Structural formula
CH2CH2
Molecular formula
C2H4
Ethanol
Structural formula
CH3CH2OH
Molecular formula
C2H5OH
Ethanoic acid
CH3COOH
Reactions of alkanes and chlorine
Alkanes react with chlorine to produce chloroalkanes.
In these reactions, one hydrogen atom is replaced by one chlorine atom.
Eg.
methane + chlorine → chloromethane + hydrogen chloride
CH4 + Cl2 –> CH3Cl + HCl
Reactions of alkenes and bromines
Alkenes react with bromine to produce dibromoalkanes.
In these reactions, two bromine atoms are added to the molecule, one to each carbon atom involved in the C=C bond.
Eg.
ethene + bromine → dibromoethane
C2H4 + Br2 –> C2H4Br2
Reaction producing esters
Alcohols react with carboxylic acids to produce esters and water.
Eg.
ethanol + ethanoic acid → ethyl ethanoate + water
C2H5OH + CH₃COOH –> CH3COOC2H5 + H2O
Esters
An organic compound, containing a –COO– group, that is produced when an alcohol reacts with a carboxylic acid.
Esters are fragrant so they are used as flavouring in food and in cosmetic products.
Propane
Structural formula
CH3CH2CH3
Molecular formula
C3H8
Butane
Structural formula
CH3CH2CH2CH3
Molecular Formula
C4H10
Propene
Structural formula
CH2CHCH3
Molecular formula
C3H6
But-1-ene
Structural formula
CH2CHCH2CH3
Molecular formula
C4H8
(Called but-1-ene because it is a chain and has an isomer)
But-2-ene
Structural formula
CH3CHCHCH3
Molecular formula
C4H8
Propan-1-ol
Structural formula
CH3CH2CH2OH
Molecular formula
C3H7OH
(Called propan-1-ol because the OH functional group is found on the first carbon atom)
Propan-2-ol
Structural formula
CH3CH(OH)CH3
Molecular formula
C3H7OH
(Called propan-2-ol because the OH functional group is found on the second carbon atom)
Butan-1-ol
Structural formula
CH3CH2CH2CH2OH
Molecular formula
C4H9OH
(Called butan-1-ol because the OH functional group is found on the first carbon atom)
Butan-2-ol
Structural formula
CH3CH2CH(OH)CH3
Molecular formula
C4H9OH
(Called butan-2-ol because the OH functional group is found on the second carbon atom)
Propanoic acid
Structural formula
CH3CH2COOH
Molecular formula
C3H6O2
Butanoic acid
Structural formula
CH3CH2CH2COOH
Molecular formula
C4H8O2
COOH
Carboxyl group
Incomplete combustion
If there is insufficient oxygen (the fuel may burn too quickly or use up the available oxygen), then the products will include carbon monoxide of carbon.
Smoke is an indicator of carbon.
Alkanes
Alkanes are saturated –> Therefore unreactive (because all electrons are occupied)
Atoms held together by strong covalent bonds.
Boiling point increases as the chain length (number of carbons) increases.
Alkanes are generally unreactive because their molecules do not contain a reactive functional group
(exception being combustion of fuels)
Reactions of alkanes
Alkanes combust in oxygen –> to form carbondioxide and water (this is bc they are fuels)
–> Its an exothermic reaction.
Incomplete combustion of alkanes leads to CO (toxic carbon monoxide) or C (soot).
Alkanes also react with chlorine.
These reactions are called substitution reactions (bc a hydrogen atom in the alkane molecule is replaced by a chlorine atom)
The reactions produce organic compounds called chloroalkanes.
Substitution reactions
A chemical reaction when an atom on a molecule is replaced by another.
This usually involves the functional group, but in alkanes it involves one of the hydrogen atoms.
How are chloroalkanes made?
Alkanes react with a Cl2 molecule. Hydrogen atom on an alkane gets substituted with a chlorine atom. (Could occur to any hydrogen atom on the carbon chain)
Ultraviolet light is needed to provide activation energy. (reaction won’t happen in the dark)
It is therefore a photochemical reaction.
(several hydrogen atoms could potentially be replaced however, it is not necessary knowledge for IGCSE chemistry –> We only need to know about monosubstitution.)
Monosubstitution
A substitution reaction in which only one hydrogen is replaced by another type of atom. For example, chloromethane.
Photochemical
A chemical reaction that needs light energy.
Cracking
The chemical reaction that breaks down larger alkane molecules to produce smaller alkane molecules and alkene molecules.
Occurs through heating and the use of a catalyst.
- Hydrogen is also produced in the reaction.
- Cracking needs high temperatures (typically about 500 °C) and a catalyst.
- Heated petroleum fractions are passed over the hot catalyst, and the products removed in a continuous process.
Ethane cracking
Ethane = C2H6
C2H4 + H2
Ethene + hydrogen
Reasons for cracking…
- Fractional distillation of petroleum –> used to produce useful mixtures of hydrocarbons.
- Fractions that contain smaller alkanes are more useful as fuels than fractions that contain larger alkanes.
- Bc alkanes consisting of smaller molecules flow more easily + are easier to ignite.
- Fractional distillation can’t produce enough of these.
–> Easier to crack large alkane molecules
Eg. Bitumen
- Cracking bitumen also produces alkenes –> useful as they are used to manufacture polymers (plastics).
Reactivity of Unsaturated vs Saturated molecules
Alkanes are saturated - Bc they contain single bonds (unreactive)
Alkenes are unsaturated - Bc they contain double bonds (reactive bc the double bonds can be broken to create single bonds with other atoms, eg. H or Cl)
Confirming the presence of unsaturated bonds in molecules
Unsaturated double bonds readily undergo a reaction with halogens such as bromine
Add a substance to a test tube of bromine water.
The bromine water changes from a brown colour to a colourless solution (Bc the C=C double bond breaks, allowing for the addition of bromine)
Reaction of alkenes with bromine. (Ethene + bromine)
The C=C double bond breaks, allowing for the addition of bromine.
CH²CH² + Br² –> CH²BrCH²Br
Ethene + Bromine –> Dibromoethene
Reactions of alkenes with hydrogen (Ethene + hydrogen)
- The addition reaction with hydrogen occurs at a temperature of approximately 200 °C in the presence of a nickel catalyst
- Reaction is sometimes referred to as hydrogenation.
- Hydrogenation is used in the production of margarines.
- By partially hydrogenating unsaturated oils that contain C=C bonds, it is possible to raise the melting point of vegetable oil so that it is solid at room temperature. Go too far with this reaction and you will actually make it less spreadable!
Ethene + Hydrogen –> Ethane
C²H⁴ + H² –> C²H⁶
Reaction of alkenes with steam (Ethene + water)
- Ethene is heated to 300 °C in the presence of steam and phosphoric acid (catalyst) –> produces ethanol.
- C=C double bond breaks, resulting in the addition of OH to produce an alcohol compound called ethanol.
- Water splits into an H atom and an –OH group.
- Both the hydrogen atom and the –OH group are added as the double bond is broken.
–> The hydrogen bonds with one of the carbons, the –OH group with the other.
Ethanol has multiple uses, eg. as a solvent and as a disinfectant that can kill bacteria.
Addition reaction
The chemical reaction when a double bond is broken in an alkene resulting in the addition of atoms to the molecule.
Two main methods of producing ethanol…
- Fermentation
- Catalytic addition of steam to ethene.
Fermentation - Production of ethanol
- Fermentation occurs in a closed system.
–> brewers must wait for the chemical reaction to be completed before they can extract the alcohol. - Fermentation to produce ethanol involves the breakdown of glucose (found in plants)
- Yeast (microorganism containing enzymes) needed for the process.
C⁶H¹2O⁶(aq) → 2C²H⁵OH(l) + 2CO²(g)
glucose → ethanol + carbon dioxide
- Enzymes in yeast breaks down sugar to produce ethanol and carbon dioxide.
This process happens in the absence of air (oxygen), and at moderate temperatures of 25–35 °C.
(Anaerobic respiration)
Addition of steam to ethene - Production of ethanol
- Ethanol = also made by addition reaction between water and ethene
–> Ethene gas obtained from cracking –> further reacted with steam to produce ethanol (process = hydration.
CH²CH² + H²O –> CH³CH²OH
- Happens at 300 °C
- Acid catalyst such as phosphoric acid.
- High pressure (60 atmospheres or 6000 kPa)
Properties of ethanol
- Liquid at room temperature
- Volatile (boiling point of 78 °C)
- Ethanol = highly flammable.
- Combustion in oxygen produces a clean blue flame (no production of soot + highly exothermic)
C²H⁵OH(l)+ 3O²(g) → 2CO²(g) + 3H²O(l)
ethanol + oxygen → carbon dioxide + water
Other substances dissolve easily in ethanol and other alcohols.
–> Bc it contains C-C bonds which is similar to other organic compounds.
–> Also it has an –OH funcitonal group –> Can be used as a solvent.
Uses of ethanol
Perfume - Volatile so evaporates easily and allows for the diffusion of the smell (also used as solvent for fragrance)
Cosmetics - Solvent + safe for human contact
Fuel - Combustion = exothermic. (If cost of obtaining ethene through cracking is too high –> ethanol is obtained through fermentation of sugars in crops/ waste plant materials (biofuel)
Hand santizer - Microorganisms can’t survive in ethanol (large amount thus found in sanitizer)
Biofuel
Fuels derived from plant based materials such as bioethanol and biodiesel. They have the advantage over conventional fossil fuels of being renewable.
Industrial scale fermentation (production of ethanol)
(Sustainability/Process/Cost/Product)
Sustainability
✔ Sustainable source.
✗ Use of crops could impact food supply.
Process
✗ Fermentation = produced in batches –> ‘One-off production / stop-start process’
Cost
✔ Inexpensive bc low temps needed.
Product
✗ Impure product –> needs to be refined by fractional distillation.
Industrial scale hydration (production of ethanol)
(Sustainability/Process/Cost/Product)
Sustainability
✗ Uses ethene obtained from fossil fuels (non-renewable resource)
Process
✔ Can produce ethanol continuously to meet market demands.
Cost
✗ Requires high temperatures + pressure –> expensive.
✔ Hydration can in an automated factory (barely any labour needed)
Product
✔ Creates pure ethanol –> no refinement.
Carboxylic acid
An organic compound containing a –COOH functional group.
Eg. CH³COOH (ethanoic acid –> Weak acid)
Methods of producing ethanoic acid
Using acid fermentation
Using acidified potassium manganate (VII)
(Both methods oxidise the ethanol - two different ways of oxidising)
Producing ethanoic acid through acid fermentation
Bacteria (eg. acetobacter) contain enzymes that catalyse the oxidation of ethanol.
Ethanol + Oxygen –> Ethanoic acid + Water
Producing ethanoic acid through acidified potassium manganate (VII)’
Potassium manganate (VII), is a strong oxidising agent (because the manganese has a +7 charge. Therefore it wants to gain electrons, which results in it losing the oxygen atoms)
It is used in the presence of sulfuric acid and heat to produce ethanoic acid
Ethanol + Oxygen –> Ethanoic acid + Water
Naming esters
Ethyl ethanoate
‘Ethyl’ –> Refers to alcohol
‘Ethanoate’ –> Refers to carbolyxic acid
How are esters formed?
Carbolyxic acid + Alcohol –> Ester + Water
Reacts in the presence of an acid catalyst (eg. sulfuric acid).
- C–O bond connecting the OH hydroxyl group in ethanoic acid breaks
- O–H bond in ethanol breaks
- The ethanol ( - H) and the ethanoic acid ( - OH), join.
- OH and H combines to form water (condensation reaction)
Polymers
Organic compounds that contain a long chain of monomer units.
Polymerisation reaction
Reaction in which monomers join to form polymers.
Addition polymerisation
When single units of an alkene (monomer) join together to form a very long chain (polymer).
How is polyethene formed?
It is an addition polymerisation reaction.
Several ethene molecules join together. The C=C bond becomes a C-C bond so it can bond with another carbon molecule.
Repeat units
Brackets around 1 or several repeating units of monomers in a sequence of monomers which becomes a polymer.
Condensation reactions
The reaction between two smaller molecules to form a larger molecule and a small molecule (eg. water).
Polyamides
Eg. Nylon
Monomers….
- A dicarboxylic acid, a molecule that contains two COOH groups
- A diamine, a molecule that contains two NH2 groups.
The OH functional group on the carboxylic acid bonds with the H atom on the NH² molecule to form water. The monomers then join to form an amide link (O=C–N–H)
What do rectangles represent in polymers?
They represent a carbon chain (easier to have that than writing out the entire carbon chain)
Polyester
Eg. PET (used in insulating fibres + plastic bottles)
Monomers…
- A dicarboxylic acid.
- A diol, a molecule containing two OH groups.
OH group on dicarboxylic acid and H atom on diol join to form a water molecule.
C atom in dicarboxylic atom joins with O atom on diol. Forms an ester link (O=C–O)
Amino acid monomer…
NH² – (R-C-R) – COOH
‘R’ - represents a unique group which defines the amino acid. Eg. CH³
Proteins
Made of amino acid monomers.
The OH of the COOH functional group and the H atom on the NH² group bond to form a water molecule.
The C atom and N atom then join between the two amino acids.
Polymer disposal
- Decomposition of plastics is slow.
- Biodegradable plastics have been invented (plastics broken down more easily by microorganisms in soil)
- Poly(ethene) plastic bags are also not sold as much due to new laws.
- Plastic is still too common and has to be disposed of somehow.
Polymer disposal in landfills
- Plastics buried in landfill + covered by soil.
- Finding land is difficult + existing sites fill up
- Plastic doesn’t actually go away
- As they break down some particles can leach into groundwater + contaminate streams/rivers
Polymer disposal through burning
- Incineration of plastics = disposal solution
- Toxic gases form
- PVC releases acidic hydrogen chloride which can’t enter the environment and has to be captured in the chimney.
