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OCR A level Chemistry > Haloalkanes > Flashcards

Haloalkanes Flashcards

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1
Q

Write the word equation for the preparation of Chloroethane from an alkane

A

Ethane + Chlorine→chloroethane

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2
Q

What are the conditions under which chloroethane is made from an alkane?

A
  • Room temperature and pressure
  • in the presence of UV radiation
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3
Q

What is the equation for the formation of chloroethane from an alkane?

A

CH3CH3 + Cl2→CH3CH2Cl + HCl

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4
Q

What is the mechanism for the formation of chloroethane from an alkane?

A

Free radical substitution

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5
Q

What are the reagents needed to make chloroethane from an alkene?

A

Ethene and HCl

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6
Q

What are the conditions needed to make chloroethane from an alkene?

A

Room temperature and pressure

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7
Q

What is the mechanism by which chloroethane can be made from an alkene?

A

Electrophilic addition

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8
Q

What is the chemical equation for the reaction of ethene and HCl to produce chloroethane?

A

H2C=CH2 + HCl →CH3CH2Cl

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9
Q

What is the atom economy for the reaction needed to make chloroethane from an alkene?

A

100%

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10
Q

Why are haloalkanes generally more reactive than alkanes?

A
  • The strength of Carbon-Halogen bonds is lower than Carbon-hydrogen bonds
  • So the Carbon-halogen bonds break more easily and allow the haloalkanes to react
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11
Q

What is the exception to haloalkanes being more reactive than alkanes? Why?

A

Fluroalkanes

  • Carbon-fluorine bonds have a higher bond enthalpy than Carbon-Hydrogen bonds
  • so require more energy to break
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12
Q

Are Carbon-Halogen bonds polar?

A

Yes

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13
Q

Why are Carbon-Halogen bonds polar?

A

Halogens have a higher electronegativity than Carbon

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14
Q

Define hydrolysis

A

A chemical reaction involving water or an aqueous solution of a hydroxide that causes the breaking of a bond in a molecule

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15
Q

What are the reagents needed to prepare an alcohol from a haloalkane by hydrolysis?

A

Haloalkane and NaOH(aq) or water

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16
Q

What are the conditions to prepare an alcohol from a haloalkane by hydrolysis?

A

Heat under reflux

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17
Q

What is the mechanism to prepare an alcohol from a haloalkane by hydrolysis?

A

Nucleophilic substitution

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18
Q

Give an equation for the reaction of bromoethane and water to produce an alcohol

A

CH3CH2Br + H2O —> CH3CH2OH + HBr

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19
Q

Define nucleophile

A

A species capable of donating a pair of electrons

20
Q

Give 3 examples of nucleophiles

A

NH3(aq), H2O, OH-(aq)

21
Q

What do most nucleophiles have in common?

A

They have lone pairs

22
Q

How do you test for the rate of hydrolysis of haloalkanes?

A

Place the test tube with haloalkane in a hot water bath, add ethanol and then AgNO3 (aq)

23
Q

Why is the experiment to test the rate of hydrolysis of haloalkanes conducted in a hot water bath?

A

To speed up the rate of reaction

24
Q

Why does the experiment to test the rate of hydrolysis of haloalkanes use ethanol?

A

Ethanol acts as a cosolvent as both water and the haloalkane dissolve in ethanol so the reactants can mix

25
Q

What are the two roles of AgNO3 (aq) in the experiment to test the rate of hydrolysis of haloalkanes?

A
  • provides H2O to act as the reactant in hydrolysis -Ag+ from AgNO3 trap halide ions released by the reaction, to form a preciptate
  • rate of precipitate production allows the rate of reaction to be calculated
26
Q

Why is water used as the nucleophile in the experiment to test the rate of hydrolysis of haloalkanes rather than AgNO3 (aq)?

A
  • if OH- ions were present they would react with Ag+ to form AgOH
  • this would form a brown precipitate
  • Ag+ ions would be removed from reacting with halides
  • any silver halide precipitate formed would be masked
27
Q

How is the rate of hydrolysis of haloalkanes compared?

A

The time taken for a visible quantity of silver halide to be formed is compared

28
Q

What colour precipitate is formed in the hydrolysis of chloroethane?

A

White

29
Q

What colour precipitate is formed in the hydrolysis of bromoethane?

A

Cream

30
Q

What colour precipitate is formed in the hydrolysis of iodoethane?

A

Yellow

31
Q

What are the relative rates of the hydrolysis of chloroethane, bromoethane, and iodoethane?

A
  • iodoethane is the fastest
  • then bromoethane
  • chloroethane is the slowest
32
Q

Why do the rates of hydrolysis of haloalkanes differ?

A

The C-Cl bond is the strongest, then the C-Br bond, then the C-I is the weakest

33
Q

What were CFCs used for?

A
  • coolants (in fridges)
  • propellant (in aerosols)
  • fire extinguishers
  • blow moulding (making plastics)
34
Q

What properties of CFCs made them good propellants/fire extinguishers/coolants?

A

They are:

  • inert
  • non-toxic
  • non-flammable
  • non-irritant
35
Q

Give the equations to show the formation of ozone in the atmosphere

A

O2 → O• + O• under UV light

O2 + O• → O3

36
Q

Why is the ozone layer important?

A

Protects organisms from high energy UV rays as O3 readily absorbs UV radiation

37
Q

What are the risks to people without the ozone layer?

A

Increased risk of genetic damage and skin cancer due to UV radiation exposure

38
Q

Why is there no overall change in concentration of ozone in the atmosphere (without human intervention)?

A

-ozone is constantly forming and breaking down at the same rate

39
Q

Why do CFCs persist in the lower atmosphere?

A

C-F and C-Cl bonds are strong and so the molecules do not break down easily

40
Q

Give the equation for the breakdown of ozone naturally within the atmosphere

A

Under the action of UV radiation O3→ O2 + O•

41
Q

Show, using equations, how Cl radicals catalyse the breakdown of ozone

A

Cl• + O2→ ClO• + O2

ClO•+ O→Cl• + O2

42
Q

Give the overall equation of the breakdown of ozone by Chlorine radicals

A

O3 + O→2O2

43
Q

Give two substances that can catalyse the breakdown of ozone

A

CF2Cl2

NO

44
Q

Where does Nitrogen monoxide come from in the atmosphere?

A

Lightning strikes and high flying aircrafts

45
Q

What type of catalysts are NO and CFCs?

A

Homogeneous

46
Q

Show, using equations, how NO radicals can catalyse the breakdown of ozone

A

NO• + O3→ NO2• + O2

NO2• + O —> NO• + O2

47
Q

Define homogeneous catalyst

A

A catalyst which is in the same phase as the reactants of the reaction it catalyses

OCR A level Chemistry (30 decks)

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