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Chemistry A-level - organic Chem > Halogenoalkanes > Flashcards

Halogenoalkanes Flashcards

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1
Q

what is a halogenoalkane ?

A

it is where a halogen takes place of a H atom in an alkane

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2
Q

uses of halogenoalkanes ? (6)

A

-refrigerants
- bases of PVC
- solvents
- teflon
- pharmaceuticals
- anaesthetics

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3
Q

in what way are halogenoalkanes the same as alkanes ?

A

they have the same carbon skeleton as an alkane

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4
Q

how reactive are halogenoalkanes compared to alkanes ?

A

halogenoalkanes are much more reactive than alkanes

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5
Q

general formula of halogenoalkanes ?

A

CnH2n+1 X
X = any halogen

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6
Q

functional group of halogenoalkanes ?

A

R-X
R = a carbon chain that can vary

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7
Q

prefixes of halogenoalkanes ?

A

iodo - , bromo - , fluoro- ,chloro-

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8
Q

what are the 4 categories of physical properties of halogenoalkanes ?

A
  • bond polarity
  • solubility
  • boiling point
  • reactivity
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9
Q

what is bond polarity associated with ?

A

electronegativity

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10
Q

what is meant by electronegativity ?

A

the power of an atom to attract a pair of electrons in a covalent bond

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11
Q

electronegativity of halogens from most to least ?

A
  • fluorine
  • chlorine
  • bromine
  • iodine
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12
Q

why do some molecules become polar ?

A

due to the difference in electronegativity

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13
Q

describe the electronegativity between C-F ?

A

fluorine is nearly twice as more electronegative than carbon
so electron density is more attracted to the fluorine, leaving carbon electron defficient ( delta positive) and Fluorine electron rich ( delta negative )

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14
Q

how many carbon bonds with halogens are polar ?

A

all bonds are polar

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15
Q

what happens to the bond polarity going up the group ?

A

bonds get more polar going up the group

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16
Q

what kind of solvent is water ?

A

water is a polar solvent

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17
Q

how is the solubility in water determined ?

A

solubility in water i determined by how strong the interactions are between the solvent ( water) and the solute that you try to dissolve

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18
Q

are halogenoalkanes soluble in water ?

A

no the are insoluble in water

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19
Q

why are halogenoalkanes insoluble in water ?

A

because even though the halogen to carbon bond is also polar, the attraction is not strong enough to make the halogenoalkane soluble in water
- also because they have large regions (r-groups) which are non-polar
so the carbon chain can only form van der waals forces

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20
Q

where are halogenoalkanes most soluble ? and why ?

A

they are most soluble in hydrocarbons
- because they are non-polar

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21
Q

what does the boiling point depend on ?

A

boiling point depends on the carbon chain length so the longer the chain the larger the boiling point

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22
Q

why does the boiling point depend on the carbon chain length ?

A

because van der waals forces increase with chain length because there are more electrons in the molecule

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23
Q

what factor reduces boiling point ? and why ?

A

branching of the chain
- because van der waals forces are weaker due to less surface area of contact for intermolecular forces to act

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24
Q

what is the boiling point trend in group 7 ?

A

boiling point increases down the group

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25
Q

why does the boiling point increase down the group ?

A

because the halogen is larger so has more electrons and greater van der waals forces which outweighs the polarity

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26
Q

halogenoalkanes that are more polar and have more electrons have what kind of boiling point ?

A

have a higher boiling point

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27
Q

what occurs almost every time when halogenoalkanes react ?

A

almost every time the C-X bond breaks

28
Q

what does the reactivity of the halogenoalkanes depend on ?

A

reactivity depends on the ease of C-X bond breaking
so if the bond breaks more easily, it will be a more reactive halogenoalkane

29
Q

what factors does the ease of bond breaking depend on ?

A
  • bond polarity
  • bond enthalpy
30
Q

what is meant by the term bond enthalpy ?

A

how much energy is required to break a covalent bond

31
Q

what is the trend of bond enthalpy in group 7 ?

A

bond enthalpy decreases going down the group

32
Q

how do you prove which one of the factors does ease depend on ?

A

by adding aqueous acidified silver nitrate solution to a halogenoalkane

33
Q

what occurs when you add aqueous acidified silver nitrate solution to halogenoalkanes ?

A

a hydrolysis reaction occurs
C-X bond breaks
halogen on ( X-) is released into the solution
so you make a precipitate of the silver hallide ( Ag X )

34
Q

iodobutane
bromobutane
chlorobutane
which precipitate forms first and what colour ?

A

iodine
yellow

35
Q

iodobutane
bromobutane
chlorobutane
which precipitate forms second and what colour ?

A

bromine
cream

36
Q

iodobutane
bromobutane
chlorobutane
which precipitate forms third and what colour ?

A

chlorine
white

37
Q

what is the conclusion of the reactivity experiment ?

A

conclusion is that reactivity increases down the group so most significant property is the bond enthalpy

38
Q

what is meant by a nucleophile ?

A

a nucleophile has a lone pair of electrons on an electronegative atom
- so they are negatively charged or delta negative

39
Q

how do nucleophiles act ?

A

nucleophiles act by using their lone pair of electrons to form a new bond

40
Q

what do nucleophiles form a bond between ?

A

form a new bond with something that is delta negative

41
Q

what are the 3 possible nucleophiles in nucleophilic substitution ?

A
  • OH- hydroxide ion
  • CN- cyanide ion
  • NH3 ammonia
42
Q

what does a nucleopjilic substitution with a hydroxide ion create ?

A

an alcohol and a halogen ion

43
Q

what does a nucleopjilic substitution with a cyanide ion create ?

A

a nitrate / nitrile and a halogen ion

44
Q

what does a nucleopjilic substitution with ammonia create ?

A

an amine and ammonium-halogen

45
Q

what does the rate of substitution depend on ?

A

the halogen

46
Q

what do mechanisms use ?

A

curly arrows

47
Q

what do curly arrows show ?

A

the movement of electrons

48
Q

what are the conditions if the reagant is NaOH ?

A

aqueous + warm

49
Q

what are the conditions if the reagant is KCN ?

A

ethanolic + warm

50
Q

what are the conditions if the reagant is NH3 ?

A

excess, concentrated ammonia dissolved with ethanol at a high pressure in a sealed container

51
Q

how many NH3 is needed in the nucleophilic substitution reaction ?

A

2

52
Q

what does NH3 act as ?

A

a base

53
Q

what are the products in the elimination reaction ?

A

an alkene
potassium - halogen
water

54
Q

what is the elimination reagant and conditions ?

A

reagant - KOH
conditions - ethanolic + hot

55
Q

what occurs in elimination ?

A

a large molecule loses an atom or group of atoms

56
Q

what does the OH- nucleophile act as ? and why ?

A

acts as a base
- because it accepts a proton (H+)

57
Q

test for alkenes ?

A

bromine water
- changes from yellow to colourless

58
Q

which H does the OH- nucleophile only react with ?

A

the adjacent carbon to make water

59
Q

what does CFC stand for ?

A

chlorofluorocarbons

60
Q

what are CFC’s ?

A

they are halogenoalkanes containing chlorine and fluorine but no hydrogen

61
Q

uses of CFC’s ?

A
  • solvents
  • refrigerants
62
Q

when the product breaks what happens to the CFC’s ?

A

the CFC’s rise up to the ozone layer

63
Q

what is the symbol for ozone ?

A

O3

64
Q

what does O3 decompose to make ?
show the equation ?

A

oxygen
2O3 -> 3O2

65
Q

why is ozone important ?

A

ozone absorbs ultraviolet light which causes cancer in humans
- life wouldn’t have evolves without the ozone layer

Chemistry A-level - organic Chem (7 decks)

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