Introduction to Organic Chemistry and Alkanes Flashcards
What is the empirical formula?
The simplest whole number ratio of atoms in a compound or molecule
What is the molecular formula?
The actual number of atoms in a molecule or element
What is the general formula?
i.e alkanes = CnH2n+2
alkenes= CnH2n
alcohols= CnH2n + 1 OH
What is the structural formula?
The arrangement of atoms in a molecule without showing all the bonds (CH3 CH2 CH2 CH2 OH)
What does the skeletal formula show?
The bonds of the carbon skeleton only. Hydrogen and carbon atoms aren’t shown, but functional groups are.
What does the displayed formula show?
The arrangement of atoms and shows all the bonds and atoms in a molecule
What is a homologous series?
A group of compounds that has the same functional group and the same general formula.
What is a functional group?
an atom or group of atoms within a molecule that has similar chemical properties
What are structural isomers?
Molecules that have the same molecular formula, but a different arrangement of atoms in space.
What are the 3 types of structural isomer?
Chain, positional, functional group
What is a chain isomer?
A molecule that has the same molecular formula, but a different arrangement of carbon atoms i.e is branched.
What is a positional isomer?
A molecule that has the same molecular formula, but a different position of the functional group
What is a functional group isomer?
A molecule that has the same molecular formula, but a different functional group
What is the functional group isomer of an aldehyde?
A ketone
What is the functional group isomer of a ketone?
An aldehyde
Where is the carbonyl group located in an aldehyde?
At the end of the molecule
Where is the carbonyl group located in a ketone?
In the middle of the molecule
What is the functional group isomer of an alcohol?
An ether
What is the functional group isomer of a carboxylic acid?
An ester
Give 3 examples of an ester?
Ethyl ethanoate , methyl propanoate, propyl methanoate
Give an example of an ether
1-ethoxy ethane
Stereoisomerism
chem vid
What is the general formula of an alkene?
CnH2n
Are alkanes and cycloalkanes saturated hydrocarbons?
Yes
What 3 ways are alkane fuels formed?
Through the fractional distillation, cracking and reforming of crude oil
What is the functional group isomer of an alkene?
A cycloalkane
What is reforming?
the processing of straight-chain hydrocarbons into branched-chain alkanes and cyclic hydrocarbons for efficient combustion.
Describe the process of fractional distillation?
1) The crude oil is vaporised in a blast furnace at about 350 degrees celcius.
2) The vaporised crude oil enters the fractioning column and rises. The longer chained hydrocarbons don’t vaporise and just run to the bottom.
3) The fractioning column has a temperature gradient, it’s cooler at the top and hotter at the bottom. As each hydrocarbon has a different boiling point, they will each cool and condense at different temperatures.
4) The hydrocarbons with the lowest boiling points don’t condense. They’re drawn off as gases at the top of the column.
What is an addition reaction?
Where 2 or more molecules are joined together to form a larger molecule
What is a polymerisation reaction?
Where lots of simple molecules are joined together to form a giant molecule
What is an elimination reaction?
Where a small group of atoms breaks away from a larger molecule
What is a substitution reaction?
Where one species is replaced by another species
What is a hydrolysis reaction?
Where a molecule is split into 2 new molecules by adding water
What is an oxidation reaction?
Where a species loses electrons in a reaction
What is a reduction reaction?
Where a species gains electrons in a reaction
Nucleophiles ……
contain a lone pair of electrons and are attracted to areas of positive charge
Electrophiles….
are electron deficient and so are attracted to areas of high electron density
Radicals….
have an unpaired electron ad are very reactive and so basically react with anything
What is gas used for?
Liquified petroleum gas (LPG) and camping gas
What is petrol used for?
What is Naptha used for?
What is Kerosene(parrafin) used for?
What is gas oil (diesel) used for?
What is mineral oil (Lubricating) used for?
What’s in greater demand- heavier fractions or lighter fractions?
Lighter fractios
What is cracking?
Breaking long chained hydrocarbons (alkanes) into shorter chained hydrocarbons (alkenes and alkanes) . It involves breaking a C-C bond
What are the 2 type of cracking?
Thermal cracking and catalytic cracking
What temperature and pressure does thermal cracking take place at?
- At high temperatures of up to 1000 degrees Celsius
- At a high pressure of up to 70 atm
What are the main products of thermal cracking?
Alkenes and hydrogen (which can be used in the haber process)
What can the alkenes produced by thermal cracking be used to make?
Polymers (plastics)
What conditions are needed for catalytic cracking?
- a zeolite catalyst
- a slight pressure
- a high temperature of around 450 degrees celcius
What compounds does catalytic cracking mostly produce?
Aromatic hydrocarbons, cyclic alkanes, branched alkanes, motor fuels
What are aromatic hydrocarbons?
compounds containing benzene rings. benzene rings contain a ring of 6 carbon atoms with a delocalised ring of electrons
How can you convert straight chained hydrocarbons into branched alkanes and cyclic hydrocarbons?
By reforming via the use of a catalyst. Hydrogen is produced as the by product of the reactions
What conditions are needed for reforming?
high pressure and high temperature in the presence of a platinum catalyst
Why does reforming hydrocarbons allow for more efficient combustion?
-Because reformed hydrocarbons have lower boiling points and so combust easier and quicker
-Reforming hydrocarbons also reduces the knocking effect, which is where alkanes explode when the fuel or air mixture in the engine is compressed.
Which pollutants are formed during the combustion of alkane fuels?
- Carbon Monoxide
- Oxides of Nitrogen
- Oxides of Sulfur
- Carbon particulates
- Unburned hydrocarbons
What happens when you burn alkanes with oxygen?
you get carbon dioxide and water
What is the possible combination of products when incomplete combustion occurs?
- Carbon monoxide, water, carbon, carbon dioxide
Why is carbon monoxide toxic?
Because the carbon monoxide binds to the haemoglobin in our blood and makes it difficult for oxygen to be transported around the body
How can carbon monoxide be removed?
By using a catalytic converter
Why are oxides of nitrogen formed?
Due to the high temperatures and pressures in the car engine
What happens when nitrogen oxides react with water?
nitric acid can be produced, which can then fall as acid rain
How is sulfur dioxide produced?
By burning fuels with sulfur impurities
What happens when sulfur dioxide is produced?
It reacts with water to form sulfuric acid and this then falls as acid rain
What problems does acid rain cause?
- Destroys plants
- Corrodes buildings and statues
- Kills fish and aquatic life living in bodies of water
How are particulates formed?
From the incomplete combustion of fuels
What problems do particulates cause?
- they can damage the lungs and cause respiratory problems
- They can cover buildings and statues, making them look unclean and accelerating corrosion
- They can reflect sunlight back into space reducing the amount of light reaching the earth, this is called global dimming
What do Catalytic converters do?
They use a platinum catalyst to convert pollutants into harmless gases, hence limiting the amount of pollutants that enter the atmosphere
What are the main fossil fuels?
Coal, oil, and natural gas
Is there a finite or infinite amount of fossil fuels?
There’s a finite amount of fossil fuels
Which fossil fuel will be the first to run out?
Oil
Are fossil fuels renewable or non-renewable?
They’re non-renewable
What are some alternatives to fossil fuels?
Biofuels and alcohol
What are the 3 main biofuels?
Bioethanol. biodiesel, biogas
What is bioethanol?
A biofuel made from the fermentation of sugar from crops such as maize
What is biodisel?
a biofuel made by refining renewable fats and oils, such as vegetable oil
What is biogas?
a biofuel produced by the breakdown of organic waste matter
Why are biofuels describes as being carbon neutral?
- This is because as the plants grow they absorb carbon dioxide which is equivalent to the amount of carbon dioxide that will be released when they are burnt.
- However, this is not completely true, as carbon dioxide will also be produced in the refining and transport of the plants
Can biodiesel and biogas also be made from waste that would otherwise go to landfill?
Yes
What is one problem with free radical substitution?
You often get a mixture of products, not just the desired product
What’s the problem with trying to use biofuels in car engines?
car engines would have to be modified and this could cost a lot of money
In alkane what does the first example of structural isomerism begin at?
Butane (C4H10)
Why do branched molecules have a lower boiling point than straight chains?
Because branched molecules are more compact and so have less London forces. This means a lesser amount if energy is required for them to boil
Are alkanes very reactive?
No, they’re fairly unreactive
What’s a trick for balancing complete combustion Equations?
- In complete combustion, every carbon in the original hydrocarbon gives a carbon dioxide.
- Every 2 hydrogens give a water molecules.
- Then all you need to do is balance the oxygen
What can SO2 be reacted with to limit its polluting effects?
So2 can be reacted with effluent gases with a suitable base compound e.g CaO
What is Carbon monoxide converted into in catalytic convertors?
To carbon dioxide
What is NOx converted into in catalytic convertors?
N2
What are unburnt hydrocarbons converted to in catalytic convertors?
C02 and H20
Which metals are usually used in catalytic convertors?
Platinum, palladium, and rhodium
Why is the catalyst in catalytic convertors used in a finely divided form?
To increase the surface area that the reaction can take place over. This increases the rate of reaction
Are alkanes aliphatic?
Yes
The greater the branching….
The lower the boiling point
Why can’t leaded petrol pass through the catalyst?
Because the lead deposit on the catalysts surface and “poisons” it. Hence blocking sites for the reaction to take place
What does heterolytic fission produce?
Ions (one gets both of the 2 electrons from the bond)
What does homylitic fission produce?
Radicals (each getting an electron each)
Can free radicals be formed during thermal cracking ?
Yes
Give the overall reaction, the initiation steps, the propagation steps, and the termination steps for the reaction of CH4 with CL2
Show the mechanism and overall equation of CH3CL reacting with Cl2
Show the mechanism and overall equation of CH2CL2 reacting with Cl2
Show the mechanism and overall equation of CHCL3 reacting with Cl2
Alkene + Halogen ->
Dihalogenoalkane
Alkene + Hydrogen ->
Alkane
Alkene + Hydrogen Halide ->
Halogenoalkane
Alkene + Potassium Mangate ->
Diol
Alkene + Steam ->
Alcohol
Why is a tertiary carbocation more likely to form?
Because it is more stable than both a primary and secondary carbocation
How many R groups is a primary carbocation bonded to ?
1
How many R groups is a secondary carbocation bonded to?
2
How many R groups is a tertiary carbocation bonded to?
3
Do symmetrical or unsymmetrical alkenes form carbocations?
Unsymmetrical
What is Markownikoff’s rule?
The major product from the addition of a hydrogen halide to an unsymmetrical alkene is the one where hydrogen adds to the carbon with the most hydrognes already attached
Thre can be a major product and a what product?
A minor product
What happens when you add an alkene to acidified potassium manganate (VII)?
The purple solution decolourises as the alkene has been oxidised and a diol has been produced.
What is an electrophile?
something attracted to areas of high electron density
What is an nucleophile?
something attracted to areas of positive charge
What conditions are needed for the hydrogenation of an alkene?
A nickel catalyst and a temperature of 150 degrees celcius
What conditions are needed for the reaction of an alkene with steam to form an alcohol?
a temperature of 300 degrees celsius; a pressure of 60-70 atm, and a solid phosphoric(V) acid catalyst
What is H3P04?
Phosphoric acid
What is KMn04?
Potassium Manganate
Why are all the reactions with alkenes examples of electrophilic addition reactions?
Because alkenes have double bonds with high electron densities that attract positively charged molecules
What type of reactions usually take place with halogenoalkanes?
Nucleophilic substitution reactions
Halogenoalkane + Aqueous Potassium Hydroxide ->
Alcohol
What conditions are needed for the reaction between a halogenoalkane and aqueous potassium hydroxide to form an alcohol?
The potassium hydroxide has to be warm and the reaction usually takes place under reflux
What happens when you react a halogeonalkane with aqueous silver nitrate in ethanol?
You get an alcohol, a hydrogen ion, and a halide ion
What can the halide ion formed from the reaction between a halogenoalkane and aqueous silver nitrate consequently react with?
The silver ions in silver nitrate to form silver precipitates. Thr colour of the precipitate allows you to identify the halide ion present.
Cl- + Ag+ ->
AgCl
Br- + Ag+ ->
AgBr
I- + Ag+ ->
AgI
What colour precipitate is AgCl?
White precipitate
What colour precipitate is AgBr?
Cream precipitate
What colour precipitate is AgI?
A yellow precipitate
Halogenoalkane + Potassium Cynaide(in ethanol) ->
Nitrile
What condition is needed for the reaction between a halogenoalkane and potassium cyanide to form a nitrile ?
Reflux
What is reflux?
Heating with a condenser placed vertically in the flask to prevent the loss of volatile substances from the mixture
What’s the benefit of the reaction between a halogeinalkane and potassium cyanide to form a nitrile?
This reaction helps lengthen the carbon chain
Halogenoalkane + Ammonia(in ethanol) ->
Amine
Halogenoalkane + Ethanolic Potassium Hydroxide ->
Alkene
What conditions are needed for the reaction of a halogenoalkane and ethanolic potassium hydroxide to form an alkene?
- The alkali potassium hydroxide must be warmed
- The mixture must be heated under reflux
- The Potassium Hydroxide must be dissolved in ethanol
What sort of reaction is the reaction between a halogenoalkane and ethanol potassium hydroxide to form an alkene ?
Elimination
Alcohol + Concentrated Phosphoric acid ->
Alkene
What type of reaction is the reaction between alcohol and concentrated phosphoric acid to form an alkene ?
An elimination reaction
What reaction conditions are needed for the reaction between an alcohol and concentrated phosphoric acid to form an alkene?
- Alcohol must be heated under reflux
- Phosphoric acid catalyst
- Alkene can be purified by distillation
What type of reaction is a dehydration reaction ?
An elimination reaction
What do alcohols combust with oxygen to give ?
Carbon dioxide and water
C2H5OH + 3O2 ->
2CO2 + 3H20
What is PCL5?
Phosphorous Pentachloride
Alcohol + PCL5 ->
Chloroalkane
Alcohol + HCl ->
Chloroalkane
Ethanol + Phosphorous Chloride ->
Chloroethane + Phosphoryl trichloride + Hydrogen Chloride
ROH + PCl5 ->
RCl + POCl3 + HCl
Alcohol + Potassium Bromide + Sulfurinc acid ->
Bromoethane + water + Potassium Hydrogen Sulfate
C2H5OH + KBr + H2SO4 ->
C2H5Br + H2O + KHSO4
What conditions are needed for the reaction of Alcohol and Potassium Bromide and Sulfuric acid ?
- Reflux
- 50% concentrated sulfuric acid
Alcohol + Red Phosphorous + Iodine ->
Iodoalkane
Oxidation of Primary alcohols….
Primary alcohols are oxidised by potassium dichromate(VI) in dilute sulfuric acid to form aldehyde and carboxylic acids
Oxidation of Secondary Alcohols…
Secondary alcohols are oxidised by Potassium Dichromate(VI) in dilute sulfuric acid to form ketones
Oxidation of tertiary alcohols….
Tertiary alcohols aren’t oxidised
Cr2O72-/H+ come from K2Cr2O7/ H2SO4
How can you get only the aldehyde product from the oxidation of primary alcohols?
Via fractional distillation
How can you test for aldehydes/ketones using Benedicts solution ?
- If benedicts is heated with an aldehyde, a red precipitate will form.
- If Benedicts is heated with a ketone, no precipitate will form
How can you test for an aldehyde/ketone using Fehlings solution?
- Red precipitate will form in the presence of an aldehyde.
- No precipitate will form in the presence of a ketone
What colour change is observed when an alcohol is oxidised with Potassium Dichromate(VI)?
A colour change from orange to green
