7. Organic Chemistry Flashcards
What is crude oil?
Crude oil is a mixture of a very large number of compounds. Most of the compounds in crude oil are hydrocarbons
How is crude oil formed?
Crude oil is formed over millions of years from the remains of ancient biomass (plants and animals), mainly plankton, that was buried in mud, under layer upon layer of rocks - in high pressures and temperatures
Where is crude oil found?
Crude oil is found in rocks
Why is crude oil a finite resource
It is being used up much faster than it is being formed
What are hydrocarbons?
Hydrocarbons are compounds that contain hydrogen and carbon atoms only
What are most of the hydrocarbons found in crude oil called?
Alkanes
What are alkanes?
- Alkanes are saturated hydrocarbons, which means they contain as many hydrogen atoms as possible for each carbon / for each molecule
- As a result, they have no double carbon bonds
What is a homologous series?
A series of compounds with similar chemical properties, the same general formula and the same functional group
What is the general formula for homologous series of alkanes?
CnH2n+2
What are the first 4 members of the alkanes?
- Methane
- Ethane
- Propane
- Butane
How can the hydrocarbons in crude oil be separated?
The hydrocarbons in crude oil can be seperated into fractions, each of which contains molecules with a similar number of carbon atoms, by fractional distillation
What is the difference between each hydrocarbon?
Each type of hydrocarbon have different number of carbon atoms and different boiling points
Longer chain hydrocarbons have a ________ boiling point
Longer chain hydrocarbons have a higher boiling point
Explain how fractional distillation of crude oil works
- The mixture of crude oil is heated and boils, whilst it is being fed to the the bottom of the fractional distillation column
- The column is kept cool at the top and hot at the bottom, so temperature decreases going up
- The gases of hydrocarbons move up the column and condense when they reach the temperature of their boiling points
- Different fractions have different boiling points, depending on how big the hydrocarbons are
- The fractions containing smaller hydrocarbons are collected at the top of the fractionating column as gases
- The fractions containing bigger hydrocarbons are collected at the lower sections of the fractionating column
- The different fractions are collected as liquids at different levels, and the liquid fractions are then removed
- The fractions are collected from the column in a continuous process
Give 2 reasons why crude oil is fractionally distilled?
- To separate them into fractions, with molecules with a similar number of carbon atoms together and similar boiling points
- Crude oil straight from the ground does not have much use
What are the distilled fractions of crude oil used for?
The disctilled fractions of crude oils are used to produce:
- Fuels (such as petrol, diesel oil and kerosene)
- Feedstock for the petrochemical industry (which produces solvents, lubricants,
polymers and detergents)
Give a reason why a huge number of different natural and synthetic carbon compounds can occur
The vast array of natural and synthetic carbon compounds can occur due to the ability of carbon atoms to form families of similar compounds
What properties do the size of hydrocarbon molecules affect?
- boiling point
- viscosity
- flammability
What affects the properties of hydrocarbon molecules?
The size of the hydrocarbon molecules
What is viscosity?
Viscosity is a measure of how easily a substance flows and how thick it is
- High viscosity means the substance is thick and it does not flow easily
- Low viscosity means the substance is runny and it flows easily
What happens as the size of a hydrocarbon’s molecules increases (gets longer)?
- The boiling point increases
- The flammability decreases
- The viscosity increases
Why are short chain hydrocarbon molecules more useful?
They are easily flammable, so they make good fuels
Why properties influence how hydrocarbons are used as fuels?
- boiling point
- viscosity
- flammability
What does the combustion of hydrocarbon fuels release?
The combustion of hydrocarbon fuels releases energy, so it is exothermic
What is complete combustion?
Complete combustion is when the hydrocarbon is burned with excess oxygen so that it is completely oxidised
What are the products of a complete combustion of a hydrocarbon?
Carbon Dioxide + Water
What happens in terms of energy during the combustion of hydrocarbons?
The combustion of hydrocarbon fuels releases energy into the surroundings, mainly by heating
What is cracking?
Cracking is the process of breaking down larger, less useful hydrocarbon molecules into smaller, more useful molecules
Why do industries carry out cracking?
There is a high demand for fuels with small molecules (as they have high flammability), so some of the products of cracking are useful as fuels which can be sold
What are the 2 types of cracking?
- Catalytic cracking
- Steam cracking
Explain how cracking works
- The fractionally distilled crude oil is placed in steel vessels called crackers
- It is then heated to vaporise the hydrocarbons
- In catalyctic cracking, the vapour is then passed over a hot catalyst, inducing cracking
- In steam cracking, the vapourised hydrocarbons are mixed with steam and are heated to an even higher temperature which induces cracking
- The hydrocarbons are cracked as thermal decomposition reactions, and breaks down in a random way which produces a mixture of smaller alkanes and also alkenes
What type of reaction is cracking
Thermal decomposition reaction
What are alkenes?
Alkenes are unsaturated hydrocarbons that contain at least one double bond between their carbon atoms
Why are alkenes more reactive than alkanes?
Alkenes are more reactive than alkanes as they have a double carbon bond, which allows alkenes to react in ways that alkanes cannot, such as with bromine water
Explain how we can test for alkenes
We can test for alkenes by reacting it with bromine water, an orange liquid, which will become decolourised if alkenes are present
What are the 2 uses of alkenes?
Alkenes are used:
- To produce polymers
- As starting materials for the production of many other chemicals
What is the general formula for the homologous series of alkenes?
CnH2n
How many fewer hydrogen atoms to alkenes have compared to alkanes?
2
What is a functional group?
A functional group is an atom or group of atoms that gives a ‘family’ of organic compounds their characteristic reactions
What is a homologous series?
A series of compounds with similar chemical properties, the same general formula and the same functional group
What is the functional group of alkenes?
C=C
Can alkenes undergo complete combustion?
Yes
What are the products when alkenes react with excess oxygen?
Carbon Dioxide & Water
When does incomplete combustion generally occur?
Incomplete combustion occurs when there is insufficient oxygen to burn
Explain why alkenes go through incomplete combustion with oxygen more than alkanes?
Alkenes tend to undergo incomplete combustion with oxygen as there is a higher carbon to hydrogen ratio (higher number of carbons) compared to alkanes
What are the products of incomplete combustion?
Carbon Monoxide & Water
What do alkenes produce when they are burned in air?
Smoky yellow flames
Why do alkenes produce smoky yellow flames when burned in air?
Alkenes produce smoky yellow flames when burned in air because of incomplete combustion
What happens when alkenes react with hydrogen, water and the halogens
The double carbon bond opens up, forming a single bond between the carbons and allowing room for two more atoms to bond, one on each carbon
Explain which 3 substances alkenes react with in addition reactions
- Hydrogen
- Water
- Halogens
Describe the reactions and conditions for the addition reaction of alkenes with hydrogen
- Alkenes react with hydrogen to break the C=C bond and form a saturated hydrocarbon - an alkane
- Hydrogenation reactions only occur at 60°C in the presence of a nickel catalyst
Describe the reactions and conditions for the addition reaction of alkenes with halogens
- In a halogenation reaction, alkenes react with halogens to break the C=C bond and produce haloalkanes
- The reaction occurs at room temperature
Describe the reactions and conditions for the addition reaction of alkenes with water
- In a hydration reaction, alkenes react with steam to produce alcohols
- The reaction requires a high temperature of 300°C, a high pressure of 60 atmospheres and phosphoric acid catalyst
What is the functional group for alcohols?
-OH
What are the first four members of a homologous series of alcohols
& their molecular formulas
Methanol
Ethanol
Propanol
Butanol
Describe what happens when alcohols react with sodium?
Give an example with ethanol
Alcohols react with sodium to form Sodium Alkoxide + Hydrogen
The alcohol and sodium start bubbling as hydrogen gas is being given off
ethanol + sodium → sodium ethoxide + hydrogen
Describe the reactions of alcohols with water
Alcohols colourlessly dissolve in water to form neutral solutions
What happens when alcohols undergo combustion (react with oxygen)?
Alcohols undergo combustion to form carbon dioxide and water
What happens when alcohols react with an oxidising agent?
Use potassium dichromate as an example
Alcohols react with oxidising agents, such as potassium dichromate, to produce a carboxylic acid and water
Explain the oxidising of ethanol
What are the main uses of alcohols?
Ethanol is the main alcohol found in alcoholic drinks
It is also used as fuel for cars and as solvents (such as ink)
List the 2 ways ethanol can be produced
Ethanol can be produced through:
- Hydration
- Fermentation
Explain how fermentation works
- Fermentation is a biological process, where a sugar solution such as glucose is mixed with yeast, which is enzymes in microscopic fungi.
- The yeast respires anaerobically using the glucose, to form aqueous solutions of ethanol and carbon dioxide as a gas
- This happens at 30°C in anaerobic conditions (where there is no oxygen)
How are carboxylic acids formed?
Carboxylic acids are formed through the oxidising of alcohols with oxidising agents
What is the functional group of carboxylic acids?
–COOH
Draw the functional group of carboxylic acids?
What are the first four members of the homologous series of carboxylic acids?
- methanoic acid
- ethanoic acid
- propanoic acid
- butanoic acid
What are the structural formulas and displayed formulas of the first 4 carboxylic acids?
Methanoic Acid - HCOOH
Ethanoic Acid - CH3COOH
Propanoic Acid - CH3CH2COOH
Butanoic Acid - CH3CH2CH2COOH
Describe the reaction between carboxylic acids and (metal) carbonates
Carboxylic acids react with (metal) carbonates to form a salt, water and carbon dioxide
What do the salts formed by the reaction of carboxylic acids all end in?
-anoate
e.g. methanoate, ethanoate
What does ethanoic acid and sodium carbonate react to form?
Describe what happens when carboxylic acids react with water?
Carboxylic acids completely dissolve in water to form weakly acidic solutions
What happens when hydrochloric acid reacts with water?
It releases hydrogen ions (H+) as well as Cl-
Explain why carboxylic acids are weak acids?
- Most of the carboxylic acid molecules stay as they are, and only a small proportion ionise in aqueous solutions.
- Furthermore, the reaction of carboxylic acid with water is also reversible, where the equillibrium lies on the left of the equation due to the low proportion of carboxylic acids ionising
- This means that a carboxylic acid solution has a higher pH (low acidity) as there is a low concentration of H+ ions
Describe what happens when carboxylic acids react with alcohols?
Carboxylic acids react with alcohols to form esters and also water
Describe the reaction (and conditions) for ethanoic acid and ethanol
- Ethanoic acid and ethanol react to form the ester (ethyl ethanoate) and water
- An acid, usually sulfuric acid, is required as a catalyst
Describe the qualities of esters
- Esters have distinct smells and are volatile (they evaporate easily)
- This makes them useful for perfumes and food colourings
What are polymers?
Polymers are large molecules that are made by joining large numbers of smal, identical molecules called monomers
What is the difference between monomers and polymers?
Monomers have a double C=C bond, whereas polymers have C-C bond
Explain what happens in addition polymerisation?
- In addition polymerisation, the monomers, which are alkenes (with C=C bonds) join together with other alkene monomers to form polymers
- The double carbon bonds on monomers break to form a single carbon bond as they form bonds with the adjacent monomer
- Explain what happens when ethene monomers join up?
- Explain what happens when propene monomers join up?
- They form poly(ethene)
- They form poly(propene)
Show the shorthand way of drawing polyethene from ethene monomers
Tips:
- Must be a single bond
- Bonds must be drawn across the brackets
- add n
Why does the the repeating unit have the same atoms as the monomer?
The repeating unit has the same atoms as the monomer because no other product is formed in the reaction
How are polymers made in condensation polymerisation?
- Polymers are made in condensation polymerisation by two different monomers, each having two of the same functional group
- The functional group at the end of one monomer reacts with the functional group on the other, creating long chains of alternating monomers,
- A small molecule - most commonly water - is also produced, hence why they are called condensation reactions
What is a diol?
A diol is a molecule with two -OH groups
What is a dicarboxylic acid?
A dicarboxylic acid is a molecule with two -COOH groups
How are polyesters made?
Polyesters are condensation polymers, that are formed by reacting a diol and a dicarboxylic acid together to form an ester and water
We can continue to add monomers of diol or dicarboxylic acids to either end of the polymer to produce a longer chain of polyester
How else can we represent a monomer of ethane diol?
How else can we represent a monomer of ethane diol?
How else can we represent a monomer of
How else can we represent a monomer of hexanedioic acid?
How can we represent the polyester:
How can we represent the polyester:
What are the products of a diol and a dicarboxylic acid reacting?
A polyester and water (2nH20)
Describe the functional groups of amino acids?
Amino acids have two different functional groups in a molecule:
- The amine group -NH2
- The carboxylic group -COOH
Explain what happens when amino acids react by condensation polymerisation?
Amino acids react by condensation polymerisation to produce
polypeptides
What is the simplest amino acid and its structural formula?
The simplest amino acid is glycine
How can two same amino acid molecules react to form a condensation polymer?
Because they have two different functional groups
What is the other product of amino acids reacting through condensation polymerisation?
Water (nH20)
How can proteins be produced?
Proteins can be produces by combining different amino acids in the same chain
What does DNA stand for?
Deoxyribonucleic Acid
What does DNA consist of?
DNA consists of two polymer chains which are made from monomers called nucleotides
What do the two polymer chains in DNA form?
The two polymer chains in DNA wrap around each other in a double helix structure
What are the 4 different nucleotide monomers?
- G
- A
- T
- C
With the exception of DNA, what are other naturally occurring polymers important for life?
- Proteins
- Starch
- Cellulose
Name the types of monomers that proteins, starch and cellulose are made of?
- Protein is a polymer made from monomers of amino acids
- Starch is a polymer made from monomers of glucose
-
Cellulose is a polymer made from monomers of glucose
The monomers of glucose in starch and cellulose are arranged in slightly different ways
