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Chemistry > Aromatic compounds > Flashcards

Aromatic compounds Flashcards

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1
Q

Aliphatic compounds

A

organic compounds where carbon aoms form open chains or closed rings but does not contain a benzene ring in their structure
eg. ethane

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2
Q

what is an aromatic compound

A

organic compounds contaning a benzene ring in their structure

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3
Q

descibe the bonding in benzene

A

six carbon-hydrogen bonds formed by sigma bonds - 12 fixed electrons
six carbon-carbon single bonds formed by sigma bonds - 12 fixed electrons

three carbon-carbon double bonds are formed by 6 pi electrons

the 6 pi electrons are delocalised-free to move around the benzene ring
the carbon carbon bonds are a identical intermediate between single and double bonds

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4
Q

what are delocalised electrons

A

freely moving electrons and are shared between More than two electrons

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5
Q

explain how the kekule structure correctly describes benzene’s structure

A

the number of
six carbon-hydrogen bonds formed by sigma bonds - 12 fixed electrons
six carbon-carbon single bonds formed by sigma bonds - 12 fixed electrons

three carbon-carbon ‘double’ bonds are formed by 6 pi electrons

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6
Q

how many electrons in benzene not involved in bonding

A

12 electrons involved not involved in bonding

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7
Q

explain how the kekule structure DOES NOT correctly describe benzene’s structure

A

does not correctly describe the distribution of pi electrons
the kekule structure has the pi electrons localised to three double bonds but in reality the electrons are delocalised
all of benzenes carbon tp carbon bonds are an identical intermediate between double and single bonds

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8
Q

give two proprties of benzene that result form its unusual bonding structure and give evidence

A

*Lack of reactivity - benzene is very stable/ unreactive
expeirmental evidence - benzene will not decolourise red bromine water or acidified potassium manganate vii
(not undergo an addition reaction)

*unusual bond lenght- all of benzenes evidence.bonds are the same lenght, smaller than a single bond, larger than an dounle

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9
Q

Is benzene saturated or unsaturated? Is it an alkene?

A

neither, benzene is neither saturated or unsaturated, also not an alkene

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10
Q

give two other properties of benzene (not related to its bonding structure)

A

non polar molecule - doesnt dissolve in water
carcinogenic- causes cancer- health hazard

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11
Q

what is the average number of electrons shared between any two adjacent carbon atoms in 1.cytohexane 2.benzene

A
  1. 2 electrons, only single bonds
  2. 2 sigma always shared +2 delocalised electrons
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12
Q

explain the result for demostarting the solubilities of methane, thene, ethyne, methylbenzene

A

result
1 when bubbled from water, each gas does not dissolve and forces itself into syringe B,syringe B opens to almost 100cm3

2 when bubbled through cyclohexane: each gas does dissolved and syringe B remains mostly closed
methane, thene, ethyne, methylbenzene are all non-polar molecules

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13
Q

name common aromatic compounds

A

pharmaceuticals - paraceramol, ibuprofen
acid base indicators- methyl orange and phenolphthalein
food preservatives - bezoic acid and its salts ( sodium benzoate)

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14
Q

name the equipment needed for extracting clove oil from cloves by steam distillation

A

safety tube
steam generator
hot plate/ bunsen burner
steam trap
cloves in water
liebig condenser
emulsion of clove oil and water

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15
Q

what are immiscible liquids

A

liquids that do not mix

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16
Q

what is the principle of steam distillation

A

the boiling point of two immiscible liquids is below the boiling point of both liquids seperately

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17
Q

Why is steam distillation used to extract clove oil from cloves rather than direct disillation

A

clove oil has high boiling point, if it were distilled directly, the oil would decompose at the high tempertures

18
Q

what is the main constituent present in clove oil, what natural product in present in clove oil

A

eugenol

19
Q

Give two saftey percautions in extracting clove oil from cloves by steam distillation

A

1 - a safety tube is placed in the steam generator to prevent build up of pressure

2- gloves are worn when handleing the cloved, eugenol can burn the skin

20
Q

comment on the positio of the saftey tube in the steam generator

A

below the water level to prevent steam from escaping

21
Q

What is the purpose of a steam trap in extracting clove oil from cloves by steam distillation

A

collect any steam that has condensed and avoid it condensing into and filling up flask full of cloved

22
Q

what two substances are collected during steam distillation

A

water and clove oil as an emulsion

23
Q

What is an emulsion?

A

An emulsion is a dispersion of small droplets of ONE LIQUID (OIL) IN ANOTHER LIQUID in which it is not soluble

24
Q

Describe the appearance of the water- clove oil emulsion/distillate collected during the steam distillation

A

Milky coloured

25
Q

Why are whole cloves used rather than powdered cloves?

A

whole cloves contain more oil

26
Q

Explain the method to Isolate clove oil from an emulsion of clove oil and water by liquid-liquid/ solvent extraction

Isolate clove oil from an emulsion of clove oil and water by liquid-liquid/ solvent extraction

A

add emulsion into a seperating funnel, using a dropper add cyclohexane.
stopper and shake(funnel is inverted when shaken) tap is opened to release the pressure of the vapourised liquid
allow aqueous layer to drain into a beaker, organic to drain seperatly into a conical flask
the aqueous layer will still contain some oil, precedure is repeated at least two more time to obtain the max amount of clove oil

27
Q

What is liquid liquid extraction

A

used to separate two immisible liquids. a slovent is added in whcih one of the liquids will dissolve but the other will not

28
Q

Why add cylohexane?

Isolate clove oil from an emulsion of clove oil and water by liquid-liquid/ solvent extraction

A

clove oil is soluble in cytohexane , water is not, adding ctyohexane dissolces the clove oil from the emulsion, doesnt dissolve water

29
Q

Saftey procedures

Isolate clove oil from an emulsion of clove oil and water by liquid-liquid/ solvent extraction

A

the eparating funnel is invertes when shaking, tap is gentaly opened to release the pressure, avoid pointing it at another person

30
Q

Why is the washing and separating carried out three times?

Isolate clove oil from an emulsion of clove oil and water by liquid-liquid/ solvent extraction

A

the milkey colour is caused by the presence of deoplets of clove oil in the water as an emulaion, each wahing ectracts more oil

31
Q

describe the methos in removing excess water

A

using a spatula, add anhydrous magnesium sulfate to the clove oil and ctyohexane mixture.
the anhydrous magnesium sulfate brinds with any water present in the mixture and forms clumps of hydrated magnesium sulfate.
filter clove oil/cytohexane mixture with flutef filter paper into a new preweighes conical flask to remove the clumps of hydrated magnesium sulfate/ excess anhydrous magnesium sulfate
rinse the orginal conical flask with cytohexane and filter again to ensure all clove oil is retrieved

32
Q

why is anhydrous magnesium sulfate (MgSO4) added

Removing excess water

A

magnesium sulfate is a drying agent, absorbs and clumps any remaining water

33
Q

How much anhydrous magnesium sulfate is added?

Removing excess water

A

add until it settles at the bottom of the flask and no longer clumps, all the water has been absorbed

34
Q

why is the mixture filtered

Removing excess water

A

to remove any hydrated magnesium sulfate and excess magnesium sulfate from the mixture

35
Q

why is fluted filter paper used

Removing excess water

A

fluted filter oaoer has a greater surface are- filtration will be quicker

36
Q

Describe the method in isolating the oil

A

place clove oil/ cytohexane in a water bath in a fume cuboard @81 C and boil the cytohexane off to leave the clove oil isolated.
leave the concial flask in the fume cuboard overnight, ensuring cyclohexane will be evaporated

37
Q

why is the filtered mixture placed under a water bath

In isolating the oil

A

cytohexane is a volatile organic solvent, boiing point in 81, the cytohexane is boiled off leaving the clove oil completely isolated behind

38
Q

why is a hot plate NOT used

In isolating the oil

A

thr clove oil could boil off as well as the cytohexane

39
Q

why is a bunsen burner not used to evaporate the cyclohexane

In isolating the oil

A

cyclohexane is a flammble solcent- it must never be heated with a bunsen burner

40
Q

two industrial uses of clove oil

A

flavoring agent
perfumes, soaps

Chemistry (27 decks)

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