Organic Chemistry Flashcards
Describe what is Meant by a Hydrocarbon
-Hydrocarbons are compounds made of hydrogen and carbon only.
-They are used as plastics, including polyester, and as fuels, including petrol and diesel.
-Only a small percentage is used for chemical synthesis.
Describe how Crude Oil is Formed
-The remains of ancient biomass of plankton fall to the bottom of the sea.
-It is covered in layers of sediment.
-Over millions of years, the pressure and temperature greatly increases.
-The high pressure and temperature cause crude oil to be formed.
Describe how Coal is Formed
-The ancient biomass of trees die and decay.
-It is covered in layers of sediment.
-Over millions of years, the pressure and temperature greatly increases.
-The high pressure and temperature cause crude oil to be formed.
Describe what is Meant by an Alkane
-Alkanes are the simplest type of hydrocarbon.
-They are all saturated (each carbon forms four single covalent bonds).
-The general formula for alkanes is CnH2n+2.
Describe the First Four Alkanes
-Methane (CH4) has one carbon.
-Ethane (C2H6) has two carbons.
-Propane (C3H8) has three carbons.
-Butane (C4H10) has four carbons.
Describe the Trend in Viscosity in Hydrocarbons
As the chain length increases, it becomes more viscous (harder to pour).
Describe the Trend in Flammability in Hydrocarbons
As the chain length increases, it becomes less flammable.
Describe the Trend in Volatility in Hydrocarbons
As the chain length increases, it becomes less volatile (harder to become a gas).
Describe the Trend in Boiling Points in Hydrocarbons
As the chain length increases, the boiling point increases.
Explain why the Boiling Point of Hydrocarbons Increases as the Chain Gets Longer
-As the chain length increases, the intermolecular forces of attraction get stronger.
-Therefore, more energy is needed to overcome these forces so the boiling point increases.
Describe the Trend in Colour in Hydrocarbons
As the chain length increases, the chains become darker in colour.
Describe what is Meant by Combustion
Combustion involves burning in the presence of oxygen.
Describe the Complete Combustion of Hydrocarbons
-Complete combustion takes place when there is enough oxygen present.
-Complete combustion produces water and carbon dioxide.
Hydrocarbon + Oxygen → Carbon Dioxide + Water
Describe the Incomplete Combustion of Hydrocarbons
-Incomplete combustion takes place when there is not enough oxygen present.
-Incomplete combustion produces water and carbon monoxide or soot.
Explain why the Combustion of Hydrocarbons is an Example of a Redox Reaction
-The carbon and hydrogen atoms both gain oxygen (and lose electrons) so they are oxidised.
-The oxygen (from the air) gains electrons so is reduced.
Describe how Fractional Distillation Separates the Hydrocarbon Chains in Crude Oil
-Fractional distillation works by separating hydrocarbons with different chain lengths based on their boiling points.
-The longer the chain, the stronger the attraction between molecules.
-The fractional distillation column has a temperature gradient, it is cooler at the top and hotter at the bottom.
-The hydrocarbons are heated until they are gases.
-The vapours rise up the column until they reach the temperature of their boiling point.
-At this point, they condense into liquids and are piped off and used, mainly as fuels.
State Different Fractions by Decreasing Boiling Point
Highest Boiling Point: Bitumen
-Heavy Fuel Oil
-Diesel Oil
-Kerosene
-Petrol
Lowest Boiling Point: Liquified Petroleum Gas
State the Uses of Crude Oil
-Oil provides the fuel for most transport.
-Some of the hydrocarbons from crude oil are used as feedstock.
-This is to make new compounds for use in things like polymers, solvents, lubricants and detergents.
Explain why Short Chain Hydrocarbons are Removed From the Fractional Distillation Column as Gases Rather than Liquids
-Very short chain hydrocarbons have very low boiling points.
-The top of the fractionating column is not cool enough for these hydrocarbons to condense.
-This means that very short chain hydrocarbons are removed as gases.
Describe what is Meant by Cracking
Cracking is the process of turning long chain hydrocarbons (high supply, low demand) into shorter hydrocarbons (low supply, high demand).
Explain why Long Chain Hydrocarbons are Cracked.
-Long chain hydrocarbons are cracked because long chain hydrocarbons are less flammable than short chain hydrocarbons.
-This means that long chain hydrocarbons are not very useful as fuels.
-By cracking them, long chain hydrocarbons are converted into short chain hydrocarbons.
-These are more flammable and are therefore more useful as fuels.
Describe the Process of Cracking
-Heat the hydrocarbons to vaporise.
-Pass them over a hot catalyst (catalytic cracking).
-OR, Heat them to a high temperature with steam (thermal cracking).
-Thermal decomposition then occurs.
-Shorter alkanes and alkenes are produced. Alkenes may be used to make other molecules such as polymers.
Describe how to Test for the Presence of Alkanes and Alkenes
-To test for the presence of alkanes and alkenes, add bromine water.
-If an alkane is present, the substance will remain the colour of bromine (orange).
-If an alkene is present, the substance will turn colourless.
Explain why Bromine Turns Colourless When Added to an Alkene
-When bromine water is added to an alkane, no reaction will happen as the alkane is saturated so it will remain orange.
-When bromine water is added to an alkene, the bromine will add across the double bond, making a colourless dibromo compound- so the bromine water is decolourised.
Describe what is Meant by an Alkene
An alkene is an unsaturated hydrocarbon (has a carbon to carbon double bond) with the general formula CnH2n.
-Alkenes have a double covalent bond between two carbon atoms.
-Because methane only has a single carbon atom, there cannot be an alkene based on methane.
Describe the Reaction of Alkenes
-Alkenes undergo addition reactions because the carbon to carbon double bond opens up to form a carbon to carbon single bond.
-This allows a new covalent bond to be formed on each carbon.
-There are no additional products formed so there is a 100% atom economy.
Explain why Alkenes Produce a Smoky Flame
-When alkenes combust, they often undergo incomplete combustion.
-This means that as well as carbon dioxide and water, carbon particles are also produced.
-Carbon particles make the flame appear smoky.
Describe the Reaction of Alkenes With Hydrogen
-Reacting alkenes with hydrogen is called hydrogenation.
-The conditions for this reaction require a nickel catalyst and a temperature of around 150℃.
-Hydrogenation is useful because it can be used to turn unsaturated fat into saturated fat.
-It is also useful because ‘Hardening’ reactions can turn oil into margarine.
Describe the Reaction of Alkenes With Steam
-Reacting alkenes with steam is called hydration.
-The conditions for this reaction are 300℃ and 70 atmospheres pressure. The catalyst is phosphoric
acid.
-Water is added across the double bond and an alcohol is formed.
Explain why Hydration Takes Place at High Pressure
-In the hydration reaction, we have two reactant molecules (the alkene and the water) and one product molecule (the alcohol). All of the molecules are gases.
-If we increase the pressure of the system, the position of the equilibrium will shift to the side with the smaller number of molecules.
-In this case, if we increase the pressure, the position of the equilibrium shifts to the right so we make more product.
Describe the Reaction of Alkenes With Halogens
-Reacting alkenes with halogens is called halogenation.
-The molecules formed are saturated, with the carbons from the double bond each becoming bonded to a halogen atom.
Compare Ethane to Ethene
-Both are hydrocarbons
-Both contain two carbon atoms per molecule
-Ethane contains six hydrogen atoms per molecule but ethene contains four hydrogen atoms per molecule
-Both have covalent bonds
-Ethane contains a single C—C bond but ethene contains a double bond
-Both contain C—H bonds
-Both small molecules
Compare the Reactions of Ethane and Ethene
-Both react with oxygen in complete combustion reactions to produce water and carbon dioxide.
-Both also react with oxygen in incomplete combustion reactions to produce water, carbon monoxide and carbon
-Ethene is more reactive than ethane.
-Ethene decolourises bromine water whereas ethane does not.
-Ethene can react with water to produce ethanol and can react with hydrogen to produce ethane.
Describe what is Meant by a Functional Group and a Homologous Series
-A homologous series is a family of compounds with the same functional group and increasing length chain of carbons.
-A functional group is part of a molecule with characteristic reactions e.g. C=C is the functional group in the alkene homologous series.
Explain why Different Alkenes React in a Similar Way
-All of the alkenes have the same functional group.
-The functional group determines how a molecule reacts.
-Because the alkenes all have the same functional group, they all react in a similar way.
State the Main Uses of Alcohols
-Alcohols are mainly used as fuels, solvents and in alcoholic drinks (ethanol).
-The functional group of an alcohol is O-H
Describe the Properties of Alcohols
-All alcohols are soluble (dissolve in) water.
-All alcohols are neutral (have pH 7).
-All alcohols are very flammable (therefore we can combust them). When alcohols are completely combusted, carbon dioxide and water are the products.
-Alcohols are highly flammable because they already contain oxygen so require less to combust.
Describe the Reaction of Alcohols with Potassium Dichromate Solution
-There is a colour change from orange to green.
-It turns an alcohol into a carboxylic acid.
-This is an oxidation process.
Describe the Reactions of Alcohols with Group 1 Metals
-The substance fizzes.
-Hydrogen gas is produced.
Explain why the Ethanol Made Through the Industrial Process Cannot be Drank
-The industrial process to create ethanol produces 100% atom economy.
-However, the ethanol produced is difficult to purify so cannot be drank.
Describe the Process of Making Ethanol by Fermentation
-Boil water (to kill bacteria).
-Add sugar (food for the yeast).
-Allow to cool (over 50℃ will kill the yeast)
-Add yeast (this is the organism with the enzymes to make ethanol).
-Leave to respire (anaerobic respiration).
State the Conditions Required to Produce Ethanol From a Sugar Solution
-This process is called fermentation.
-Yeast needs to be added.
-Warm and anaerobic conditions are needed.
State the Advantages of Hydration
-The reaction produces a high yield of ethanol.
-The reaction can produce any alcohol, not just ethanol.
State the Disadvantages of Hydration
-This reaction requires a high temperature, needing a lot of energy.
-The starting material comes from crude oil which is non renewable.
State the Advantages of Fermentation
-This reaction requires a low temperature so not much energy is needed.
-The starting material comes from plants and is therefore renewable.
State the Disadvantages of Fermentation
-This reaction can only be used to make the alcohol ethanol.
-This makes an aqueous solution of ethanol. Distilling the ethanol requires energy.
Explain why the Reaction to Produce Carboxylic Acid is an Example of Oxidation
-Turning alcohol into a carboxylic acid is an example of oxidation because there is a gain of oxygen.
-An alcohol contains one oxygen whereas a carboxylic acid contains two.
-The functional group of carboxylic acids is H-O-C=O
Describe the Properties of Carboxylic Acids
-Carboxylic acids are weak acids. This means they partially ionise when dissolved in water.
-Because carboxylic acids are weak acids, they have a relatively low concentration of H+ which means that they have a relatively high pH value compared to strong acids.
Describe the Reactions of Carboxylic Acids
-A carboxylic acid reacts with a metal to produce a salt and hydrogen.
-A carboxylic acid reacts with a metal carbonate to produce a salt and water and carbon dioxide.
-A carboxylic acid reacts with alcohols to make an ester.
Describe how Esters are Made
-A carboxylic acid reacts with an alcohol via a condensation reaction to make an ester and water.
-It is a reversible reaction. An acid catalyst is usually used (e.g. sulfuric acid).
-The functional group of an ester is O=C-O
Describe the Uses of Esters
-Esters have strong, sweet smells. This means they are often used in food flavourings and perfumes.
-They are also good at dissolving organic compounds so are often used as solvents.
Describe how the Yield of Ethyl Ethanoate can be Increased
-We can force the position of the equilibrium to the right (products) by increasing the concentration of the reactants.
-This means the system increases the yield of the products.
Describe what is Meant by Polymerisation
-Polymerisation is the joining of many repeated units (monomers) to make long chain molecules (polymers).
-Plastics are an example of polymers.
Describe Addition Polymerisation
-In addition polymerisation, the monomer needs a carbon to carbon double bond. Therefore, alkenes are used.
-The long chain has the same atoms as the monomer because no other molecule is formed in the reaction.
-There is 100% atom economy.
-The double bond in the monomer breaks to add other monomers.
Describe Condensation Polymerisation
-Condensation polymerisation involves monomers which contain different functional groups.
-The monomers react together and bonds form between them, making polymer chains.
-Condensation polymers are made from diols and dicarboxylic acids.
-For each new bond that forms, a small molecule (e.g. water) is lost.
Explain why Polyester Melts When Heated
-Polyester is thermosoftening.
-It has no cross links.
-This means it can be reshaped into new products.
Compare Addition Polymerisation to Condensation Polymerisation
Addition Polymerisation:
-1 monomer is used
-Formed from alkenes
-No co-products are produced
-100% atom economy
Condensation Polymerisation:
-Formed from 2 monomers
-Formed from a diol and a dicarboxylic acid
-Water is produced
-The atom economy is less than 100%
Describe the Monomers Used to Make Polypeptides (Proteins)
-The monomer used to make a polypeptide is an amino acid.
-An amino acid contains two different functional groups- a basic amino group (NH2) and an acidic carboxyl group (COOH).
-The group underneath the carbon makes each amino acid unique.
-Polypeptides are made by condensation polymerisation (so water is also made).
Describe the Monomers Used to Make Polysaccharides
-The monomer used to make a polysaccharide is glucose. Examples include starch and cellulose.
-Starch is a linear form of glucose whereas cellulose is a branched form of glucose.
-Polysaccharides are made by condensation polymerisation (so water is also made).
Describe the Monomers Which Make up DNA
-DNA (Deoxyribonucleic Acid) is a polynucleotide made from nucleotide monomers.
-A nucleotide is made up of a phosphate group, a sugar (Ribose) and a base.
-DNA exists as two polynucleotide chains joined together to make a double helix.
Describe the Shape and Structure of DNA
-There are two polymer chains.
-These are made up of four different monomers.
-It is shaped as a double helix.
