C7: Organic chemistry Flashcards
What makes something “organic” in the chemical sense?
It contains carbon.
What is crude oil?
- A finite resource found in rocks: the remains of an ancient biomass, consisting mainly of plankton that was buried in mud.
- Is a mixture of a large number of compounds, mostly hydrocarbons.
What are hydrocarbons?
Molecules made only of hydrogen and carbon.
Most of the hydrocarbons in crude oil are what?
Alkanes.
What is the general formula for alkanes?
CnH2n + 2
What is meant by the term “homologous series”?
A series of compounds with the same functional group and similar chemical properties.
What are the names of the first four members of the alkanes?
- Methane
- Ethane
- Propane
- Butane
What is fractional distillation and what is its purpose?
- The process by which hydrocarbons in crude oil are separated into fractions.
- The fractions can be processed to produce fuels and feedstock for the petrochemical industry.
Explain how the process of fractional distillation works.
- Crude oil is heated until the hydrocarbons evaporate.
- The hydrocarbons rise through the column.
- The hydrocarbons condense and different fractions are extracted in different parts of the column.
- Longer hydrocarbons condense in the lower parts of the column; shorter ones in the upper parts.
Name 5 fuels produced by fractional distillation from crude oil.
- Petrol
- Diesel oil
- Kerosene
- Heavy fuel oil
- Liquefied petroleum gases
Name 4 useful materials produced by the petrochemical industry.
- Solvents
- Lubricants
- Polymers
- Detergents
Why is there such a vast array of natural and synthetic carbon compounds?
Carbon atoms have the ability to form families of similar compounds (homologous series).
What 3 properties of hydrocarbons depend on the size of molecules?
- volatility (boiling points)
- viscosity (runniness)
- flammability
For hydrocarbons, how does boiling point change with increasing molecular size?
- Longer hydrocarbon chains have more cumulative intermolecular forces which require more energy to overcome
- So their boiling points are higher
- Shorter chains have less cumulative intermolecular forces, so it takes less energy to separate molecules
- So they are more volatile
For hydrocarbons, how does viscosity change with increasing molecular size?
- Longer hydrocarbon chains have more cumulative intermolecular forces which require more energy to overcome
- So they are more viscous
- Shorter chains have less cumulative intermolecular forces, so it takes less energy to separate molecules
- So they are less viscous
For hydrocarbons, how does flammability change with increasing molecular size?
- Longer hydrocarbon chains have more cumulative intermolecular forces which require more energy to overcome
- So they are less flammable
- Shorter chains have less cumulative intermolecular forces, so it takes less energy to separate molecules
- So they are more flammable
What happens during the combustion of hydrocarbons?
- The carbon and hydrogen in the fuels are oxidised
- Energy is released
Write the general equation for the complete combustion of a hydrocarbon.
Hydrocarbon + oxygen → carbon dioxide + water
What are alkenes?
Hydrocarbons with the functional group C=C (with a double carbon-carbon bond).
What is cracking and what is its purpose?
- The process by which long-chain hydrocarbons are broken down to produce smaller, more useful molecules by thermal decomposition
- The products of cracking are alkanes and alkenes
- Some of the products of cracking - the small ones - are used for fuels because they are flammable
How are alkenes (produced by cracking) useful?
- Used to produce polymers
- Used as starting materials for the production of many chemicals
Name 2 types of cracking.
- Catalytic cracking
- Steam cracking
Describe the conditions used for catalytic cracking.
- It is a thermal decomposition reaction
- Long-chain hydrocarbons are heated and vaporised
- Vapour is passed over a powdered aluminium oxide catalyst
- The molecules split apart on the surface of the specks of catalyst
Describe the conditions used for steam cracking.
- It is a thermal decomposition reaction
- Long-chain hydrocarbons are heated and vaporised
- Vapour is mixed with steam and heated to a very high temperature
- The molecules split apart
Which are more reactive: alkanes or alkenes?
Alkenes.
How would you test for alkenes?
- Add bromine water, which is bright orange
- Positive result: solution goes colourless
What is the general formula for alkenes?
CnH2n
Which out of alkanes and alkenes are saturated and unsaturated? Explain why.
- Alkanes are saturated because all C-C bonds are single.
- Alkenes are unsaturated because they contain a double C-C bond (C=C).
What are the names of the first four alkenes?
- Ethene
- Propene
- Butene
- Pentene
How do alkenes combust?
- Alkenes can react completely with oxygen in the same way as all hydrocarbons.
- But they tend to react incompletely, burning with a smoky flame.
How do alkenes react with hydrogen?
Addition reactions:
- Hydrogen is added across the C=C bond
- The C=C bond then becomes a C-C bond
- Each of the carbons in that bond is bonded to one hydrogen atom
- The molecule becomes saturated
How do alkenes react with the halogens?
Addition reactions:
- The halogen is added across the C=C bond
- The C=C bond then becomes a C-C bond
- Each of the carbons in that bond is bonded to one halogen atom
- The molecule becomes saturated
How do alkenes react with water?
Addition reactions:
- When alkenes are reacted with steam, alcohols are formed
- Water is added across the C=C bond
- The C=C bond then becomes a C-C bond
- Each of the carbons in that bond is bonded to one hydrogen atom. One carbon also bonds like this: C-O-H
- The molecule becomes saturated
What is the functional group of alcohols?
-O-H
What is the general formula of alcohols?
CnH2n+1OH
What are the names of the first four alcohols?
- Methanol
- Ethanol
- Propanol
- Butanol
Describe what happens when one of the first 4 alcohols burns in air.
- They are flammable so combust completely in air
- This produces carbon dioxide and water
Describe what happens when one of the first four alcohols is added to water.
They dissolve, forming neutral pH solutions.
Describe what happens when one of the first four alcohols reacts with an oxidising agent.
They react with oxygen to produce carboxylic acids.
Describe what happens when one of the first four alcohols reacts with sodium.
- This produces sodium []oxide and hydrogen gas.
- Ethanol reacts to produce sodium ethoxide and hydrogen gas.
What happens when sugar solutions are fermented using yeast? What should the conditions be for fermentation?
- Happens fastest at 37°C, in a slightly acidic solution and under anaerobic conditions
- An aqueous solution of ethanol is produced (an enzyme in yeast converts the sugar to ethanol)
Name 2 uses of alcohols.
- Solvents
- Fuels
Why are alcohols used in solvents?
They can dissolve most things that water can, but also things that water cannot (hydrocarbons, oils, fats).
How are alcohols used as fuels?
The first 4 are used as fuels, because they are flammable.
What is the functional group of carboxylic acids?
-C-O-O-H
What are the names of the first 4 carboxylic acids?
- Methanoic acid
- Ethanoic acid
- Propanoic acid
- Butanoic acid
What is the general formula of carboxylic acids?
CnH2n+1COOH
Describe what happens when any of the first 4 carboxylic acids reacts with carbonates.
They react to produce a salt (ending in “anoate”), water and carbon dioxide.
ethanoic acid + sodium carbonate →
sodium ethanoate + water + carbon dioxide
Describe what happens when one of the first 4 carboxylic acids are placed in water.
They dissolve, then ionise (but not completely), resulting in a weakly acidic solution.
Why are carboxylic acids weak?
- When placed in water, they dissolve, then ionise, resulting in an acidic solution
- But they don’t ionise completely (not all acid molecules release H+ ions)
- So they only form weak acidic solutions
- This means they have a higher pH than that of solutions, of the same concentration, of strong acids
Describe what happens when alcohols react with carboxylic acids.
They react to produce esters.
What is the functional group of esters?
-C-O-O
ethanoic acid + ethanol →
ethyl ethanoate + water
Name 2 types of polymerisation.
- Addition polymerisation
- Condensation polymerisation
What happens during addition polymerisation?
Many small molecules (monomers: alkenes) join together to form very large molecules (polymers).
Draw a diagrame to represent poly(ethene).
What happens during condensation polymerisation?
Monomers with 2 different functional groups join together, usually losing small molecules such as water. The polymers formed contain 2 monomer types.
Name 5 naturally occuring polymers.
- Amino acids
- Proteins
- DNA
- Starch
- Cellulose
How do amino acids polymerise?
- Amino acids have 2 different functional groups within a molecule
- So they react by condensation polymerisation, producing polypeptides
- Different amino acids are combined in chains to produce proteins, which are also polymers
What is DNA?
DNA (deoxyribonucleic acid) is a large molecule, essential for life, which encodes genetic instructions for the development and function of living organisms and viruses.
DNA is a polymer. Describe its structure.
Most DNA molecules are two polymer chains, made from four different monomers called nucleotides, in the form of a double helix.
Name the monomer which the polymers proteins are made from.
Amino acids.
Name the monomer which the polymer starch is made from.
Glucose.
Name the monomer which the polymer cellulose is made from.
Glucose.
