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Chemistry mark scheme flashcards > haloalkanes > Flashcards

haloalkanes Flashcards

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1
Q

Name the type of mechanism used to turn haloalkanes into an alcohol (1)

A

nucleophillic substitution

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2
Q

State and explain how the rates of hydrolysis of the chloroalkane and the bromoalkane would differ (2)

A
  • rate slower with chloroalkane
  • C-Cl bond is stronger than C-Br bond
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3
Q

What measurment and observation would allow the student to compare the rates of hydrolysis (1)

A

time for precipitate to appear

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4
Q

1-iodopentane was found to react faster than 1-bromopentane Explain why. (2)

A
  • C-I bond is weaker thane C-Br bond
  • Carbon - halogen bond breaks
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5
Q

Alcohol are used in organic synthesis
pentan-2-ol can be prepared by the alkaline hydrolysis of 2 - iodopentane
the reaction mixture is boiled for 20 minutes
State the most appropriate technique that could be used to boil the reaction mixture for 20 minutes (1)

A

reflux

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6
Q

The rate of the hydolysis of a haloalkane depends on the halogen present State and explain how the halogen in the haloalkane affects the rate of hydrolysis (2)

A
  • links rate of reaction to strength of bond /bond enthalpy eg the weaker the bond the fater the reaction stronger bond takes longer to break lower bond enthalpy reacts faster
  • C-F bond is hydrolysed slowest
  • C-I bond is hydrolysed faster than C-Br
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7
Q

the organic product in (i) can be formed faster uing a different haloalkane than 1 - bromobutane identify the haloalkane and explain your answer (1)

A
  • 1-iodobutane
  • C-I bonds are weaker
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8
Q

Give two sources of nitrogen oxides in the stratosphere (1)

A
  • lightning
  • aircraft
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9
Q

What does a curly arrow represent in mechanisms (1)

A

movement of an electron pair

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10
Q

What is meant by the term nucleophile (1)

A

electron pair donor

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11
Q

Radical substitution produces a mixture of organic products
Sugget two reason why (2)

A
  • further substitution
  • substitution at different positions along a chain
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12
Q

State two properties that make a good aerosol (1)

A
  • low reactivity
  • volaatile
  • non toxic
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13
Q

Explain the following statements using equation where appropriate
* life on earth benefits from the precence of an ozone layer
* the concentration of ozone maintained in the ozone layer
* how CF2Cl2 produces radical which catalye the breakdown of the ozone (5)

A
  • benefit of ozone layer to life - ozone absorbs UV radiation
  • maintenane of O2 concentration - O3 reverible arrow O2 + O
  • production of radicals from compound - CFCL2 -> Cl + CF2Cl
  • breakdown of O3 - Cl +O3 ->CLO + O2
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14
Q

Give chemical explanations for the folowing statements
The rate of hydolysis of 1 - bromobutane is faster than that of 1 - chlorobutane (1)

A

The C-Br bond is weaker than the C-Cl bond

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15
Q

What is meant by the term structural isomers (1)

A
  • having the same molecular formula but different structural formula
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16
Q

Suggest why an alkene is less soluble in water than either of alcohols (2)

A
  • does not contain Oh groups
  • does not form hydrogen bond with water
17
Q

Suggest how CH3O- (methoxide ion) can act as a nucleophile (1)

A
  • it is an electron pair donor
18
Q

In this mechanism explain how CH3O- ions have acted a a nucleophile and suggest the type of bond fission that takes place (1)

A
  • CH3O- donates an electron pair
  • and heterolytic fission
19
Q

Explain how CH3O- ions have acted a a base in the mechanism (1)

A

CH3O- accepted a proton

20
Q

What do experimental reults tell you about the carbon - halogen bond enthalpies (1)

A

bond enthalpy decreases C-Cl>C-Br>C-I

21
Q

Predict an approximate value for the bond angles in a molecule of CF3Cl (1)

A
  • 108-111
22
Q

Suggest a property than made CF3Cl uitable as a propellant in an aerosol (1)

A
  • volatile / low boiling / gas / non toxic / non flammable / unreactive/ liquidies under pressure / inert
23
Q

Explain what is meant by the tern homolytic fission (2)

A
  • bond pair split equally
  • bond breaking
24
Q

Suggest which bond is most likely to be broken when CF3Cl is exposed to ultraviolet radiation Explain your answer (2)

A
  • C-CL because it is the weaker bond
25
Q

Identify the two free radicals most likely to be formed when CF3Cl is exposed to ultraviolet radiation (2)

A
  • Cl
  • CF3
26
Q

Suggest two reasons why there is still concern about ozone depletion (2)

A
  • CFCs take many years to reach the ozon layer or long residence time
  • CFCs are still being used
  • there are other ozone depleting substances
27
Q

As part of an experiment he inhaled a lung full of dichlorodifluoromethane CCL2F2 and used it to blow out a candle
use the demenstration to suggest two properties of CCL2F2 explain with a reason two other uses of the chemicals such as CCl2F2 other than a refrigerant (4)

A
  • non toxic
  • non flammable
  • aerosols - because it is volatile / unreactive/ non toxic
  • degreasing agent - good solvent for organic material
  • fire extinguishers - because it is non flammable

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