Organic Chem exam qs

Question 1

How to demonstrate ethene readily undergoes addition reaction with bromine water

Answer 1

• bubble/add ethene into bromine water (solution)

- brown bromine solution decolorised

Question 2

would you expect benzene to readily undergo an addition reaction with bromine waer?

Answer 2

• no
• benzene is table/benzene has no double bonds/benzene bonds intermediate between double and single / benzene readily undergoes substitution

Question 3

explain delocalised

Answer 3

-shared between more than two atoms / shared by more than one bonded pair of atoms / moving (not fixed) between one pair of bonded atoms and another

Question 4

how many electrons in a benzene molecule are delocalised?

Answer 4

6

Question 5

how many electrons in a benzene molecule are involved in sigma bonds between carbon atoms?

Answer 5

12

Question 6

health hazard associated with benzene

Answer 6

carcinogenic

Question 7

effect of adding tetraethyllead to an equimolar mixture of methane and chlorine exposed to weak sunlight

Answer 7

• reaction rate increases

- tetraethyllead acts as a catalyst / tetraethyllead provides ethyl free radicals

Question 8

explain fractionation of crude oil

Answer 8

separation into components according to molecular size/by distillation

Question 9

components of liquid petroleum gas

Answer 9

propane

butane

Question 10

LPG

Answer 10

liquid petroleum gas

Question 11

drawing propan-1-ol

Answer 11

draw a bond between the OH functional group when drawing molecules such as propan-1-ol just in case

Question 12

why boiling pt of propanal is higher than that of butane

Answer 12

• propanal has dipole-dipole forces/propanal is polar/has a polar CO
• butane has weaker intermolecular forces/butane is non-polar

Question 13

why boiling pt of ethanoic acid is higher than that of propan-1-ol

Answer 13

• ethanoic acid has stronger/more hydrogen bonding than propan-1-ol
• ethanoic acid has polar OH and CO bonds/has two polar groups
• propan-1-ol molecule only has a polar OH bond/one polar group

Question 14

organic product of reaction of propanal with KMnO4

Answer 14

propanoic acid

Question 15

spectroscopic technique that could help confirm identity of a sample of eugenol

Answer 15

IR spectrometry or spectroscopy

Question 16

hydrocarbon gas produced by anaerobic bacterial decomposition of either animal waste or vegetation

Answer 16

methane

Question 17

polymer of ethene

Answer 17

polyethene

Question 18

how does the geometry around the carbon atoms change in the conversion of ethanol to ethene?

Answer 18

tetrahedral to planar

Question 19

effect of presence of tetraethyllead in the conversion of ethane to chloroethane

Answer 19

incrases rate/speeds up reaction by providing ethyl free radicals

Question 20

carbonyl group in an ester

Answer 20

it is the c and o (double bonded), does not count the single bond o

Question 21

testing for aldehydes (2 methods)

Answer 21

• Mix Fehling’s 1 and 2
• Add to aldehyde and mix
• Heat gently
• Blue soln to red ppt is positive result

OR

• Add Tollen’s Reagent in clean test tube
• Add aldehyde, mix
• heat gently
• silver mirror is positive result

Question 22

reactions of carboxylic acids

Answer 22

on table

Question 23

test for unsaturation

Answer 23

Alkenes, alkynes decolourise bromine water

equation on table

Question 24

safe disposal of sodium resides

Answer 24

on table

Question 25

when naming alkenes

Answer 25

indicate where double bond is in IUPAC names eg. 1-butene (bond on the end)

Question 26

why catalytic cracking, dehydro etc are carried out

Answer 26

- inc octane number | - make more useful compounds

Question 27

colour change as phenylmethanol is converted to benzoic acid, explain this colour change by reference to the transition metal used

Answer 27

purple to brown to colourless MnO₄⁻ (Mn(IV)) changes to Mn²⁺ (Mn(II))

Question 28

effect of adding tetraethyllead in conversion of alkane to chloroalkane

Answer 28

tetraethyllead increases rate by providing ethyl free radicals

Question 29

"circle the carbonyl group in this ester"

Answer 29

circle both the C and the O (the double bonded one)

Question 30

explain whether or not the kekule model correctly describes (i) the number, and (ii) the distribution of pi electrons in benzene

Answer 30

(i) yes, each of the 3 double bonds has 2 pi electrons | (ii) electrons in benzene are delocalised

Question 31

experimental evidence for delocalised electrons in benzene

Answer 31

All C-C bonds in benzene are of the same length, does not decolourise bromine water easily

Question 32

bonds broken and formed on conversion of propanone to propan-2-ol

Answer 32

broken: pi bond of CO (carbonyl) formed: OH, and CH

Question 33

alkene intermolecular bonds

Answer 33

has Van der Waals forces between the molecules

Question 34

alcohols intermolecular bonds

Answer 34

has hydrogen bonding between the molecules

Question 35

ketones intermolecular bonds

Answer 35

has dipole-dipole forces between the molecules

Question 36

"identify a carbon atom in planar geometry in this ester"

Answer 36

the carbonyl group will be the planar carbon

Question 37

why propane has a lower bp than butane

Answer 37

propane: smaller Mr | therefore weaker intermolecular forces between molecules

Question 38

homologous series

Answer 38

same functional group / similar chemical properties

Question 39

how geometry is changed when ethene converted to ethane

Answer 39

mention bond angles, how it changes from bond angle of x to bond angle of y

Question 40

why alkenes are more reactive than alkanes

Answer 40

- presence of double bond | - which can donate electrons /high electron density

Question 41

identify alcohol propanone is converted to

Answer 41

propan-2-ol its a secondary alcohol so make sure to specify instead of just writing "propanol"

Question 42

why propanone doesnt react with fehling's reagent even tho propanal does

Answer 42

propanone not oxidised easily

Question 43

bonds broken and formed on conversion from ethanol to ethene

Answer 43

broken: C-H and C-O formed: C=C and O-H

Question 44

another organic compound besides ethanal that could be formed when ethanol is oxidised using acidified sodium dichromate

Answer 44

ethanoic acid | primary alcohol, cant be ketone? i guess?