A2 - Structures, reactions & properties of commercially important organic compunds Flashcards
(21 cards)
name the type of reaction that takes place when an alkane burns in oxygen
Combustion
write an equation to show how butane will undergo complete combustion
C4H10 + 6.5O2 —-> 4CO2 + 5H2O
write an equation to show how propane will undergo complete combustion
C3H8 + 5O2 —> 3CO2 + 4H2O
write an equation to show how decane will undergo complete combustion
C10H22 + 15.5O2 —> 10CO2 + 11H2O
put these alkanes in order from highest to lowest boiling point; CH4, C4H10, C512, C2H6 & C3H8
highest boiling point ———— lowest boiling point
C5H12, C4H10, C3H8, C2H6 & CH4
explain your answer about the order of alkanes from the highest boiling point to the lowest boiling point
as the size of the molecule increases the boiling point increases - this is because there are more electrons which create stronger IMF attractions
explain why C4H10 is a gas but C8H18 is a liquid at room temperature
C8H18 has a higher boiling point than C4H10 because C8H18 has more electrons than C4H10, so C8H18 has stronger IMF attractions
why does 2,2-dimethylbutane have a lower boiling point in comparison to hexane
2,2-dimethylbutane has the most branches so it will have the fewest points of contact between its molecules - therefore, it has the weakest IMF attractions
what are the bond angles for the orbitals in each type of hybridisation?
sp - 180 sp^2 - 120 sp^3 - 109.5
describe the process of sp^3 hybridisation for a carbon atom
- 1 s and 3 p orbitals mix together
- there are 0 spare p orbitals
- this forms 4 sp^3 hybrid orbitals
- the energy of the s orbital increases
- the energy of the p orbital decreases
- each orbital holds 1 electron
- the hybrid orbitals have the same shape
what is the definition of a free radical
a free radical is a species with an unpaired electron
Br-Br —> Br. + Br.
Identify the type of bond fission shown in the initiation step
homolytic fission
State what happens to the free radicals in a termination step
free radicals combine and form a molecule
Describe how ultraviolet light causes a reaction to begin
the UV light breaks the halogen bond - this forms two radicals
Name the compound
H H H H
| | | |
H — C—C—C—C— H
| | | |
H H Br H
2-bromobutane
Start from RIGHT SIDE ~ use lowest no.
CH3CH2CH3 + Br2 —> CH3CH2CH2Br + Hbr
Describe how ultraviolet light causes reaction to begin
UV light breaks halogen bone, Br2 which is needed for homolytic fission
Br2 —> 2Br •
Why does propene able to form 2 bromoalkanes?
Because it has an asymmetrical structure ~ 2 different haloalkanes can be made when alkene is asymmetrical
Name the bromoalkane
H H Br
| | |
H—C—C—C—H
| | |
H H H
1-bromopropane
H H H H H H
| | | | | |
H —C—C—C + H—C—C—C—H
| | | | + |
H H H H H
Carbocation A Carbocation B
Compare stability of carbocation A with carbocation B.
Carbocation A is less stable than carbocation B ~ it is only bonded to 1 carbon ~ named primary, 1^o
Whereas carbocation B (C+) is bonded to 2 carbons ~ so it’s MORE stable ~ named secondary, 2^o ~ so there’s a greater POSITIVE INDUCTIVE EFFECT (more e- donated to C+)
What is the type of reaction used in free radical polymerisation of alkenes?
Addition
discuss the advantages & disadvantages of manufacture of ethanol by hydration if ethene
- fermentation is irreversible - all reactants become products
- hydration is reversible - not all reactants become products
- hydration requires MORE raw materials; ethene and H2O
- fermentation uses renewable sources whilst crude oil is NON-RENEWABLE, plants take in CO2 when growing (carbon neutral - does NOT release CO2)
- fermentation has SLOW rate of reaction
- impure ethanol made needs DISTILLING
- hydration requires higher temps - increases cots but this does INCREASE rate of reaction
- hydration - phosphoric acid is corrosive (more DANGEROUS than yeast)
