Topic 6-Organic Chemistry

Question 1

1.

what is the homolous series

Answer 1

the homologous series of a group of compounds have the same functional group and general formula

Question 2

what do you use the general formula of alkenes to work out

Answer 2

molecular formula of a compound- Alkenes have the general Formula CnH2n (where ‘n’ is the number of carbon atoms)
the molecular formula of an alkene with 23 carbon- C23 H(2X23)= C23H46

Question 3

what do sucessive members of the same homologous series increase by?

Answer 3

CH2
methanol- CH3OH
Ethanol- CH3CH2OH
Propanol- CH3CH2CH2OH
Butanol- CH3CH2CH2CH2OH

Question 4

general formula of alcohols

Answer 4

CnH2n+1OH

Question 5

nomenclature

IUPAC STEPS

Answer 5

1.Find the length of the stem by counting the longest continuous chain of carbons
2. the functional groups on the molecule normally tells you the ending of the name (suffix)
3. number the carbon chain so that the functional group sits on the lowest possible number carbon.
4. make a notes of the carbon number the-OH is attached to. Place this number before the suffix.
5. any side chains and less important functional groups are written as prefixes in alphabetical order
6. if there is more than one 1 identical functional group or side chain put di(2) tri-(3) or tetra-(4)

look on notes for example

Question 6

classifying reactions

polymerisation

Answer 6

joining smaller monomers together to form very long chain

Question 7

addition

Answer 7

joining moleules together to form longer ones

Question 8

substitution

Answer 8

replacing one atom with another on amolecule

Question 9

elimination

Answer 9

some atoms break away from larger molecules

Question 10

what do mechanisms show

Answer 10

a chemical mechanism shows the movement of electrons during a chemical reaction.
we use curly arrows to show the movement of a pair of electrons. they always start from an area with electrons eg a double bond or lone pair
and they end where you are moving the electrons to or the formation of a new bond.f

Question 11

Types of mechanisms

Answer 11

nucleophilic subsitution- used in primary halogenoalkanes and aqeous potassium hydroxide to make alcohols. amines are made by reacting halogenealkenes with ammonia

radical substitution- used in reactig halogens to alkanes (alkanes are quite unreactive) to make halogenoalkenes.

electrophilic addition- used in adding halogens and hydrogen halides to alkenes to make halogenoalkanes.

Question 12

structural isomers- chain isomerism

Answer 12

structural isomers have the same molecular formula but a different strcutural formula but a different structural formula. there are three types of structural isomers
1. chain
2. 2.positional
3. 3.functional group

Question 13

positional isomers

Answer 13

same molecular formula but different position of the functional group on the carbon skeleton
eg pentan-1-ol, and pentan-2-ol, alcohol group is sitting in different positions

Question 14

functional group isomers-same molecular forrmula but different functional group

Answer 14

eg penr-1-ene
and cyclopentane
looped carbons together

Question 15

spotting isomer

Answer 15

you must draw an isomer and not the same molecule just drawn in adifferent shape
fid the longest continuous chain of carbons irrespective of shape

Question 16

alkanes

Answer 16

alkanes are saturated hydrocarbons with the general formula CnH2n+2
alkanes are hydrocarbons which means they contains hydogen and carbon only
they are saturates which means each carbon is bonded 4 times with the maximum number of hydrogen possible
cycloalkenes are slightly different they have the general formula of CnH2n which 2 hydrogens per carbon. see diagram
cycloalkenes have a different general formula to a normal alkene- they are still saturated and they are a functional group isomer of alkenes

Question 17

bond fission
2 types of bond fission exist- homolyctic and heterolytic

Answer 17

bond fission is the breaking of a covalent bond. the electron pair in the bond can be distrubuted in 2 ways
heterolytic fission- the bond breaks but the electrons are distributed unequally to form 2 different ions ( a cation and an anion)
the double headed arrow shows the movement of a pair of electrons
‘hetero’ means ‘different’
SEE DIAGRAM
homolyctic fission- the bond breaks with the pair of electrons in the bond being shared equally to form 2 uncharged radicals
the dot means there is an unpaired electron on the atom.
‘Homo’ means ‘same’

Question 18

free radical chain reactions
radicals are highly reactive
alkanes are not similar electronegativity c and H, hand have strong bonds.

Answer 18

chain reactions involve 3 main stages- initiation, propagation and termination
intiation- the bond breaks producing 2 radicals
propagation- radical reacts with a non radical. new radigals are created which then go on to react with other non-radicals. - hence chain reaction
termination- when 2 radicals react they form a non-radical molecule. this ends the chain reaction. ths why its called termination.
see example

Question 19

fractional distillation

Answer 19

the vaporised oil enters the column and rises through the trays. the lomgest hydrocarbons dont vaporise and run down to the bottom

the column has a temperature gradient. it is cooler on top. as the vapour rises parts of the mixture condenses at different temperatures.
this is because there are different chain lengths hence different boiling poits
the fractions are drawn off at different levels
shortest hydrocarbons such as butanes and methanes wont even condense at 20C and so comes off as a gas at the top of the column.

Question 20

uses fractional distillation

Answer 20

Gas- used in LPG and stove gas
Kerosine-used as jet fuel and heating
diesel oil- used as diesel fuel
fuel oil- used in ships and power stations
bitumen- roofing and tarmac
petrol- used in petrol cars

Question 21

cracking

Answer 21

fractional distillation produces a variety of fractions however demand for each fraction varies
we can take the heavier fractions and crack them. cracking is breaking a longer chain alkane to shorter hydrocarbons
heavier fractions like fuel oil are in lower demand than lighter fractions such as petrol which are more valuable.
C12H26 – c2h4 + c10h22
dodecane ethene decane

Question 22

Thermal cracking

Answer 22

High temperature and pressure used 1000C, 70atm of pressure
Products of thermal cracking are mainly Alkenes
Alkenes are used to make polymers such as plastics eg propane is used to make poly(propene)

Question 23

Catalytic cracking

Answer 23

High temperature and slight pressures
used 450C
A zeolite catalyst is used which helps lower the temperature needed
Using a zeolite catalyst lowers the temperature and pressure needed for cracking to occur. This lowers costs and speeds up the process
Products of catalytic cracking are mainly aromatic hydrocarbons useful in fuels for vehicles. (Aromatic compounds contain benzene rings which is 6 carbons in ring with a delocalised electron system.)

Question 24

Reforming alkanes

Answer 24

Alkanes can be reformed into cycle Alkenes and aromatic molecules
Petrol and diesel are made of a mixture of hydrocarbons some of which are straight chain hydrocarbons
The problem is straight chain alkanes create knocking in a car engine. Knocking is where straight chain alkanes explode upon compression.
Adding branched cyclic alkanes reduces knocking and increases engine efficiency .
Cyclic and branched alkanes can be made using straight chain alkanes and a platinum catalyst in a process called reforming.

Question 25

Complete combustion of alkanes

Answer 25

Alkanes burn is oxygen completely (plentiful supply of O2) to form co2 and water H20 Alkanes are good fuels as most burn readily to produce large amounts of energy. The longer the alkane the more energy produces The complete combustion of butane C4H10 +6.5O2 —> 4O2 + 5H2O

Question 26

Incomplete combustion of alkanes

Answer 26

Soot is pure , produces by longer hydrocarbons When alkanes burn with a limited oxygen supply we produce carbon monoxide (CO) and carbon (soot). Incomplete combustion occurs The incomplete combustion of butane producing Co and/or Co2: C4H10 (g)+ 4.5O2(g) —> 4CO (g)+5H20(g) C4H10(g) +5.5O2(g) —> 2CO2(g) +5H20(g) Carbon monoxide is poisonous as it bonds to haemoglobin in the blood and prevents oxygen bonding. Carbon monoxide can be removed using a catalytic converter. The incomplete combustion of butane producing C (soot) C4H10(g) + 2.5O2(g) —> 4C(s) + 5H2O(g) Soot can cause breathing problems, making buildings dirty and clog up engines.

Question 27

Acid rain

Answer 27

Burning fossil fuels can release sulphur dioxide and oxides of nitrogen which contribute to acid rain Some fossil fuels contain sulfur based impurities. When burned the sulfur reacts with oxygen producing sulfur dioxide (SO2) Oxides of nitrogen (NOx) These are produced when nitrogen and oxygen (from the air) are heated in the engine and react. Oxides of nitrogen dissolve in water in the atmosphere to form nitric acid which contribute to acid rain.

Question 28

Catalytic converters ( are found mainly in vehicles and help reduce harmful pollutants entering the atmosphere

Answer 28

Catalytic converters help to reduce the amount of unburnt hydrocarbons and oxides of nitrogen going into the atmosphere Catalytic converters normally contain platinum, rhodium and iridium metals. They convert harmful gases like carbon monoxide, oxides of nitrogen, unburnt hydrocarbons —-> to less harmful products like water vapour, nitrogen, carbon dioxide Eg nitrogen monoxide is being converted to nitrogen and oxygen 2NO(g) —> N2(g) +O2(g)

Question 29

Unlike fossil fuels, Biofuels (Bioethanol, biodiesel and biogas are all renewable sources of energy).

Answer 29

Ethanol is being used as a fuel in countries where there is a good supply of sugar cane. Brazil is one of the biggest users of biofuels (bioethanol). This is added to petrol Sugar is fermented to produce the alcohol. Advantages Biofuels are renewable Biofuels produce Co2 but the Co2 gets absorbed by plants- so is carbon neutral Disadvantages Expensive to convert existing petrol engines to take fuels with a higher concentration of ethanol. Land that could have been used to grow food is being used to make fuel. This could cause food shortages in countries that grow sugar cane eg Brazil.

Question 30

Introduction to alkenes

Answer 30

Alkenes are unsaturated hydrocarbons with the general formula CnH2n They are unsaturated - double bond, high electron density Alkenes where double bonds are

Question 31

what are steroisomers

Answer 31

have the same structural formula but a different arrangement of atoms in space. An example is E/Z isomers

Question 32

What does E mean what does Z mean

Answer 32

E- Entgagen (opposite)- same groups opposite the double bond Z-Zusammen(together)- same groups on the same side of the double group.

Question 33

what is an eletrophile

Answer 33

any positive ion or molecule, which is attracted to a region of high electron density. eg H¬Br, positive hydrogen atom is acting as an eletrophile.

Question 34

hydration of alkenes

Answer 34

water + alkenes ---> alcohols which is known as a hydration reaction ethene+ water makes ethanol - water is in the form of steam - phosphoric acid is used as a catalyst - temperature is 300 degrees C, Pressure 60 atm learn mechanism see notes

Question 35

Test if substance in unsaturated

Answer 35

add drops bromine water (orange) gently shake the test tube substance is unsaturated, product colourless substance is saturated, product is orange

Question 36

Uses of polymers

Answer 36

Polymers are unreactive hydrocarbon chains with multiple strong, non-polar covalent bonds. This makes them useful for manufacturing many everyday plastic products such as poly(ethene) shopping pags. However, the unreactive nature of the bonds in addition polymers means they are not biodegradable and cannot be broken down by species in nature.

Question 37

Disposal of polymers

Answer 37

Addition polymers are non-biodegradable which means disposal of them can be difficult. Waste polymers can be processed in different ways. Some can be recycled, some are used as feedstock for cracking and some are incinerated to produce energy for other industrial processes. Incineration can release toxic gases which must be removed to reduce the impact on the environment. As well as this, scientists are developing biodegradable polymers to overcome these waste issues.

Question 38

Primary, secondary and teritary Alcohols

Answer 38

Naming alcohols- CH3OH- methanol When there is more than one C it’s you can say position of OH, eg Propan-1-ol When there is two OH you use ‘di’ and you don’t drop the ‘e’ eg ethane-1,2-diol When there is three OH you use ‘tri’ eg propane-1,2,3-triol Certain functional groups have naming priority over the alcohol functional group eg aldehydes, ketones, and carboxhylic acids eg eg 3-hydroxypropanal Primary alcohols - OH is bonded to Carbon is bonded to one other carbon Secondary alcohols- OH is bonded to carbon is bonded to 2 other carbons Teritary alcohols - OH is bonded to carbon is bonded to 3 other carbons

Question 39

Haloalkanes, with one halogen have general formula, CnH2n+1X, X is halogen

Answer 39

Same primary, secondary teritary rule as alcohols The carbon to halogen bond is polar, halogen atoms are electronegative slight negative halogen Haloalkanes have higher boiling points than their equivalent alkanes Alkanes are non polar molecules so intermolecular forces are London forces, London forces are relatively weak and require little energy to break so alkanes have relatively low boiling points In haloalkanes, we also find London forces, because of polarity between the carbon and halogen bond so we find permant dipole which are stronger than London forces. Haloalkanes are insoluble in water- they can’t form hydrogen bonds, haloalkanes are soluble in non polar solvents such as cyclohexane

Question 40

Electrophilic

Answer 40

Alkene + Halogen —-> Dihalogenalkane

Question 41

Nucleophiles

Answer 41

All nucleophiles have a lone pair of electrons. This lone pair of electrons is attracted to an electron deficient carbon atom. Electron deficient carbon atoms have a positive charge, either a full positive charge or a partial positive charge The nucleophile donates the lone pair of electrons to form a covalent bond between the nucleophile and the carbon atom

Question 42

To measure rate of hydrolysis (haloalkanes nucleophilicsubstitution)

Answer 42

We use aqueous silver nitrate Each test tube you place 1cm3 of ethanol 0.1 c,3 of haloalkanes to each test tube Then place each test tube in water bath at 60c At cooler temperatures hydrolysis is very slow In separate test tube we add aqueous silver nitrate and place this tube into the same water bath Wait 10minutes for all the solutions to reach same temperature Then we add 1cm3 of silver nitrate to each test tube and start timing Water is nucleophile and is solvent Water molecule reacts with haloalkanes by nucleophilic substitution Cl-(aqueous) + Ag+(aqueous) ——> AgCl(s) silver chloride (white precipitate) very slowly Br-(aqueous) + Ag+(aqueous) ——> AgBr(s) silverbromine (cream precipitate) slowly I-(aqueous) + Ag+(aqueous) ——> AgCl(s) silveriodine (yellow precipitate) Rapid Fastest to slowest :Iodoalkane > bromoalkane > chloroalkane Chloroine is most electronegative requires a lot of energy to overcome electrostatic forces of attraction C-Cl