C7 - organic chemistry Flashcards
What is cracking
cracking is the process by which longer chain hydrocarbons are split into shorter, more useful hydrocarbons. Cracking results in an alkane and alkene generally.
Why are the products of cracking useful?
(1) shorter hydrocarbons make better fuels
(2) shorter alkenes can also be used as feedstock to make polymers and detergents in petrochemical industry
What type of reaction is cracking an example of?
A thermal decomposition reaction - i.e breaking down molecules by heating them
What catalyst is used in catalytic cracking?
Hot powdered aluminium oxide
What is the process for catalytic cracking?
(1) First, some long chain alkanes are heated until they vaporise into a gas
(2) Then they’re passed over a hot, powdered aluminium oxide catalyst
(3)This breaks the long chain alkanes into a shorter chain alkane and an alkene
How is steam cracking different to catalytic cracking?
There is no catalyst involved. Instead the vaporised long chain alkane is mixed with steam at very high temperatures.
What are the first 4 alkenes?
2 carbons – ethene
3 carbons – propene
4 carbons – butene
5 carbons – pentene
What are alkenes?
Hydrocarbons with a double bond between the two carbon atoms.
Why is there not an alkene called methene?
Methene would indicate that there is only 1 carbon atom, and so there would not be a carbon - carbon double bond, which means the molecule wouldn’t be an alkene.
Are alkenes saturated?
No. They are unsaturated as they have a carbon - carbon double bond.
What is the general formula for alkenes?
C nH2n
What is the test for alkenes?
- add bromine water
- colour changes from orange —–>colourless if alkenes are present.
Why are alkenes more reactive than alkanes?
Alkenes have a carbon - carbon double bond, which is very reactive.
What is a functional group?
a group of atoms in a molecule which determine how the molecule reacts
What chemical test can we use to distinguish alkanes and alkenes?
(1) add orange bromine water and shake
(2) if it is a saturated compound like an alkane it will remain orange
(3) if its an unsaturated compound like an alkene is will go colourless.
What type of reaction can a alkene be a part of because of its double bond?
addition reactions
How do addition reactions work?
the carbon - carbon double bond breaks up and and opens up, then a new atom is added to each carbon
What are addition reactions?
when two molecules combine to form a single molecule
What is hydrogenation?
addition of hydrogen to an alkene in the presence of a catalyst. Forms an alkane
How does hydrogenation work?
(addition reaction between an alkene and hydrogen)
(1) an alkene reacts with hydrogen in the presence of a catalyst
(2) this gets rid of the double bond, and adds hydrogen to each carbon.
How do alkenes form alcohol?
(addition reaction between alkene and water)
(1) they react with steam (gaseous water at h.temp) in presence of catalyst
(2) this breaks the double bond, hydrogen goes on one side, OH goes on the other.
(3) then we separate the alcohol
What happens with alkenes react with a halogen?
The double bond will break, and each carbon will bond to a halogen atom, produce a halogenoalkane.
Do alkanes tend to undergo complete or incomplete combustion?
alkanes usually combust completely
Do alkenes tend to undergo complete or incomplete combustion?
alkenes often undergo incomplete combustion
What is incomplete combustion?
combustion without sufficient oxygen to react completely
What are the drawbacks of incomplete combustion?
(1) a smoky yellow flame
(2)less energy releases
(3) produces pollutants
What harmful products can be produced by the incomplete combustion of hydrocarbons?
(1) carbon
(2) carbon monoxide
(3) unburnt hydrocarbons.
What is a monomer?
one of the small repeating units that join together to form a larger molecule, known as a polymer.
What is a polymer?
a larger molecule formed from lots of smaller molecules (monomers)
What is polymerisation?
the process by which lots of small molecules(monomers) join together to form a larger molecule (a polymer)
What 2 conditions are usually necessary for polymerisation
(1) high pressure
(2) presence of a catalyst
What are addition polymers formed from?
Addition polymers are former from unsaturated monomers (monomers with double bonds), like alkenes.
How do you name polymers?
Place the same of the monomer in brackets and put the phrase ‘poly’ in front of it.
For example, the polymer of ethene would be ‘poly(ethene)’
What would the polymer of chloropentene be called?
Poly(chloropentene)
How do addition polymers form?
The carbon - carbon double bonds within the monomers break, and allow the two monomer molecules to bond to each other.
What are 3 things to remember when drawing monomers and repeating units?
(1) draw bonds of monomer vertically up and down
(2) have empty bonds go through the bracket in repeating unit
(3) have ‘n’ to signify large number of monomers and repeating units.
What is the general formula for alcohols?
CnH2n+1OH
What is alcohol’s functional group?
OH
Name the first 4 alcohols.
1 carbon - methanol
2 carbons - ethanol
3 carbons - propanol
4 carbons - butanol
(replace the alkanes’ ‘e’ with ‘ol’
What are the 4 properties of alcohols?
(1) they are flammable
(2) they are all soluble in water (with a neutral pH)
(3) they react with sodium to form hydrogen
(4) they oxidise to form carboxylic acids
What are 3 things alcohols are used for?
(1) alcoholic drinks
(2) solvents
(3) fuels
Which alcohol molecule is used in alcoholic drinks?
ethanol
Why are alcohols used as solvents?
They can dissolve lots of different substances, including hydrocarbons, oils and fats.
What are the products of the combustion of alcohols?
combustion of alcohols produces water and carbon dioxide
What is the general word equation for the complete combustion of an alcohol?
alcohol + oxygen –> carbon dioxide +water
What is ethanol?
ethanol is an alcohol with the formula CH3CH2OH
Give 3 uses of ethanol
(1) as chemical feedstock to produce other compounds
(2) as a biofuel (ethanol can be burned like petrol
(3) alcoholic drinks - beers, wines
How is ethanol made from ethene?
Ethanol can be produced by ethene and steam.
React ethene C2H4 with water (gaseous H2O)
- addition reaction
What is the word and symbol equation for the reaction of making ethanol from ethene?
ethene + steam –> ethanol
C2H4 + H2O –> C2H5OH
What are the pros and cons of making ethanol from ethene?
PROS: ethene is cheap and the reaction itself is cheap and efficient
CONS: ethene is made from crude oil which is a non- renewable resource
What does the term ‘fermentation’ mean with reference to ethanol?
Fermentation is the anaerobic respiration of sugars by yeast cells to produce ethanol and carbon dioxide.
What is the word and symbol equation for the reaction of making ethanol by fermentation?
glucose–> ethanol + carbon dioxide
C6H12O6 –> CH3CH2OH + CO2
What are the conditions for fermentation?
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.
What are the pros and cons of making ethanol by fermentation?
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.
Why are temperatures of 30 - 40 C used when making ethanol by fermentation?
This is the optimum temperature for the enzymes
What are the condition of making ethanol from ethene?
Conditions: High temperature (300 °C), high pressure (60-70 atm), phosphoric acid catalyst.
What is the functional group of a carboxylic acid?
-COOH
How are carboxylic acids names?
all end with ‘anoic acid’. eg. ‘propanoic acid’
Name the first 4 carboxylic acids
1 carbon - methanoic acid
2 carbons - ethanoic acid
3 carbons - propanoic acid
4 carbons - butanoic acid
Are carboxylic acids neutral, acidic or alkaline?
acidic
How do carboxylic acids react with water?
(1) they dissolve in water but they don’t completely ionise (release H+ ions)
(2) they form weak acidic solutions
(3) this gives them a high pH for an acid ( 5 or 6)
The ionisation of carboxylic acids in water can be shown as an equilibrium reaction like this:
C3H7COOH ⇌ C3H7COO- + H+
It is always the H+ attached to the OH group that ionises. The other hydrogen atoms are strongly bonded to the carbon atoms.
How do carboxylic acids react with carbonates?
They form salt, water and carbon dioxide.
(e.g. ethanoic acid + potassium carbonate —> potassium ethanoate + water + carbon dioxide)
Are carboxylic acids strong or weak acids?
weak acids
When carboxylic acids react with carbonates, how are alts named?
all end with ‘anoate’ e.g. ‘sodium ethanoate’
What type of substance reacts with an alcohol to form a carboxylic acid?
oxidising agent.
What is the functional group of an ester?
-COOH-
What are esters formed from?
An ester is made by reacting a carboxylic acid and an alcohol in the presence of an acid catalyst (such as sulfuric acid).
What are some uses of esters?
In perfumes and food flavourings - because they smell sweet and fruity
What are the properties of esters?
- pleasant smells
- volatile (evaporate easily)
What by-product is formed during the reaction which forms and ester and how?
Carboxylic acids react with alcohols to form esters.
In the reaction, the carboxylic acid loses its OH group, and the alcohol loses the H from its OH group. These then combine to form water (H2O).
Which names can be used for the functional group of an ester?
Ester link
Ester group
Ester bond
What do we call the aster that is formed from ethanol and ethanoic acid?
Ethanoic acid + ethanol ➔ Ethyl ethanoate
What is condensation polymerisation?
The process by which monomers combine to form a polymer, while releasing small by - products such as water.
What is the general formula for making a polyester?
dicarboxylic acid monomer +diol monomer –> polyester + water
For polyesters, how does condensation polymerisation work?
A dicarboxylic acid (carboxylic acid with 2 COOH groups) and a diol (alcohol with 2 OH groups) bond together.
As a part of this process, the diol and dicarboxylic acid lose hydrogen and oxygen, which bond together to form water.
Which two functional groups are involved in forming a polyester?
Carboxyl group (COOH) and alcohol group(OH)
What does biodegradable mean?
Biodegradable means that the substance can be broken down by naturally occurring organisms (i.e. it can decay)
Are both addition polymers and condensation polymers biodegradable?
Only condensation polymers are biodegradable.
What is important when making condensation polymers?
- each monomer has to have at least 2 functional groups
- at least 2 different functional groups overall
- small molecule given off in the process.
Which 2 different functional groups are present in all amino acids.
(1) amino group (NH2)
(2) Carboxyl group (COOH)
How are polypeptides made?
Condensation polymerisation between amino acids.
What are one (or more) long chains of polypeptides knows as?
Proteins - when a polypeptide folds up or combines with another.
What does DNA stand for?
Deoxyribonucleic acid
Which functional groups does an amino acid have?
Carboxylic acid
An ‘R’ group
An amino group
What type of reaction takes place when amino acids combine to form a polypeptide?
Condensation reaction
Which of the following names can be used to refer to the bond formed in a condensation reaction between amino acids?
Amide bond
Amide link
Peptide bond
What is DNA made of?
2 polymer chains (each made of monomers called nucleotides) wrapped around each other in the shape of a double helix to prevent damage.
Which letters do we use to represent the four nucleotides that make up DNA?
T A G C
What are sugars?
Sugars are small molecules containing:
(1) carbon
(2) oxygen
(3) hydrogen
What do multiple sugars form when combined together?
Sugars can form larger carbohydrate polymers (also knows as polysaccharides), via polymerisation reactions.
What are some examples of naturally occurring polymers?
(1) proteins
(2) DNA
(3) Polypeptides
Give examples of carbohydrate monomers:
Glucose
Fructose
Give examples of carbohydrate polymers:
Starch
Cellulose
Glycogen
