DF - organic reactions *02

Question 1

Complete combustion

Answer 1

When an organic compound is burnt completely in oxygen
-alkanes, cycloalkanes, alkenes, alcohols

produce carbon dioxide and water

very exothermic
- so make great fuels

Question 2

equation for complete combustion of alkanes

Answer 2

CH4 (g) + 2O2 (g) –> CO2 (g) + H2O (g)

Question 3

equation for complete combustion of cycloalkanes

Answer 3

C4H8 (g) + 6O2 (g) –> 4CO2 (g) + 4H2O (g)

Question 4

equation for complete combustion of alkenes

Answer 4

C4H8 (g) + 6O2 (g) –> 4CO2 (g) + 4H2O (g)

Question 5

equation for complete combustion of alcohols

Answer 5

CH3OH (l) + 1,1/2 O2 (g) –> CO2 (g) + 2H2O (g)

Question 6

Incomplete combustion

Answer 6

when there is not enough oxygen organic compounds cannot burn completely

produce carbon monoxide and water

Question 7

equation for incomplete combustion of alkanes

Answer 7

CH4 (g) + 1/2O2 (g) –> CO (g) + 2H2O

Question 8

equation for incomplete combustion of cycloalkanes

Answer 8

C4H8 (g) + 4O2 (g) –> 4CO (g) + 4H2O (g)

Question 9

equation for incomplete combustion of alkenes

Answer 9

C4H8 (g) + 4O2 (g) –> 4CO (g) + 4H2O (g)

Question 10

equation for incomplete combustion of alcohols

Answer 10

CH3OH (l) + O2 (g) –> CO (g) + 2H2O (g)

Question 11

addition reactions of alkenes - w/ bromine

Answer 11

DRAW THIS
Electrophilic additon
1. the double bond repels the electrons in Br2, polarising Br-Br
2. heterolytic fission of Br2. The closer Br (the +ve one) gives up the bonding electrons to the other Br and sticks to the carbon atom
3. get a +vely charged carbonation intermediate, the Br- now zooms over…
4. …and bonds with the other C atom.

Forms: 1,2-dibromoethane

Question 12

How do you test for an electrophilic addition with alkene and bromine?

Answer 12

If you add Cl- ions to an ethene and bromine mixture you will also get, CH2BrCH2Cl

this is evidence for electrophilic addition
- once ethene has reacted with bromine to form the carbocation, it can react with either another bromide ion or the chloride ion

Question 13

addition reaction of alkenes - w/ hydrogen halides

Answer 13

DRAW THIS
Electrophilic addition
1. the double bond repels the electrons in HBr, polarising H-Br
2. heterolytic fission of HBr. The H (the +ve one) gives up the bonding electrons to the Br and sticks to the carbon atom
3. get a +vely charged carbonation intermediate, the Br- now zooms over…
4. …and bonds with the other C atom.

Forms: 1-bromoethane (bromoalkanes)

Question 14

alkene –> alkane ?

Answer 14

adding hydrogen to C=C bonds produces alkanes

needs nickel catalyst, 150degrees and high pressure
OR
needs a platinum catalyst, RTP

Question 15

ethene –> ethane

Answer 15

ethene will react with hydrogen gas to produce ethane
- needs a catalyst (nickel), temp. 150c and high pressure
OR
- platinum catalyst at RTP

Question 16

Test for C=C bond?

Answer 16

Bromine water.
1. when you shake an alkene with orange bromine water it decolourises quickly
2. forms a dibromoalkane
H2C=CH2 + Br2 –> CH2BrCH2Br
3. tests for all unsaturated compounds ( double or triple bonds)

it is electrophilic addition

Question 17

PAG 7

Question 18

Addition reactions of alkenes - w/ water and H2SO4 catalyst

Answer 18

this is hydration and produces an alcohol
1. cold conc. sulfuric acid reacts with an alkene in an electrophilic addition reaction
ethene + sulfuric acid –> ethyl hydrogen sulfate
H2C=CH2 + H2SO4 –> CH3CH2OSO2OH

2. add cold water and warm the product its hydrolysed to form an alcohol
   ethyl hydrogen sulfate + water –> ethanol + sulfuric acid
   CH3CH2OSO2OH + H2O –> CH3CH2OH + H2SO4

Overall reaction:
H2C=CH2 + H2O –[H2SO4]–> C2H5OH

Question 19

Addition reactions of alkenes - w/ steam

Answer 19

To produce ethanol
ethene can be hydrated by steam at 300degreesC and 60atm with a solid phosphoric(v) acid catalyst

H2C=CH2 < —> C2H5OH

the reaction is reversable and the reaction yield is low (5%)
- BUT can recycle unreacted ethene gas making overall yield 95%