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Chemistry > Haloalkanes > Flashcards

Haloalkanes Flashcards

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1
Q

Why are haloalkanes more reactive than alkanes? (3)

A

Contain polar bonds
C-halogen bond is polar as the halogen has a greater electronegativity than the carbon atom
This means that the C atom will be attacked by a nucleophile

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2
Q

What is meant by a nucleophile? (1)

A

A species which can donate a lone pair of electrons

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3
Q

What is a nucleophilic substitution reaction? (1)

A

When a halogen is replaced by a nucleophile

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4
Q

What is formed by hydroxide ions (from haloalkanes) in nucleophilic substitution (1)

A

Alcohol

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5
Q

Reagent and condition of nucleophilic substitution to form alcohol (2)

A

NaOH
Aqueous, heat under reflux

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6
Q

What is formed by cyanide ions (from haloalkanes) in nucleophilic substitution (1)

A

Nitriles

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7
Q

Reagent and condition of nucleophilic substitution to form nitriles (2)

A

KCN
Water and ethanol

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8
Q

What is formed by ammonia (from haloalkanes) in nucleophilic substitution (1)

A

Amine

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9
Q

Reagent and condition of nucleophilic substitution to form amines (5)

A

Ammonia
Excess, ethanol solvent, heat and pressure

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10
Q

Nucleophilic substitution of a haloalkane using hydroxide ions can also be called what? (1)

A

Hydrolysis

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11
Q

Method to determine the rate of reaction of hydrolysis of haloalkanes (6)

A

Place a measured sample of each halogenoalkane into separate test tubes and place into water bath at 50 degrees Celsius
Into another test tube place a solution of ethanol, water and aqueous silver nitrate and place in the same water bath
Once at equal temperature add equal volumes of ethanol mixture and haloalkane solutions together
Time how long it takes for each precipitate to form
The rate of reaction can be determined by calculating 1/time taken for the precipitate to occur

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12
Q

What is the reason for the differing rates of hydrolysis of haloalkanes? (1)

A

Bond enthalpy (heat energy needed to break a bond)

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13
Q

How does bond enthalpy affect the rate of hydrolysis of haloalkanes (3)

A

As the bond enthalpy increases, the bond gets stronger and is harder to break
More energy required to break it
Slower rate of reaction

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14
Q

Weakest carbon-halogen bond (1)

A

Carbon - iodine

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15
Q

Strongest carbon-halogen bond (1)

A

Carbon - chlorine

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16
Q

When forming amine through nucleophilic substitution, what is the role of the ammonia molecule acting in each stage of the mechanism? (2)

A

The first NH3 is a nucleophile because it donates a pair of electrons to the carbon atom
The second NH3 acts a base because it accepts a hydrogen

17
Q

Mechanism to produce alkenes from haloalkanes (1)

A

Elimination

18
Q

Reagents and conditions of elimination to form alkenes (2)

A

KOH
hot, ethanolic

19
Q

What is the role of hydroxide ions in an elimination reaction? (1)

A

Act as a base as they remove a hydrogen from the molecule

20
Q

How is ozone formed naturally in the upper atmosphere (stratosphere) (1)

A

Free radical reaction

21
Q

Why is an ozone layer important? (2)

A

Acts as a barrier to the harmful UV-B radiation as it absorbs UV radiation

22
Q

What are the useful properties of chlorofluorocarbons (CFCs)? (3)

A

Non-toxic
Inert gases
Volatile

23
Q

Why have CFCs been banned to be used as solvents and refrigerants (1)

A

To slow down depletion of ozone layer

24
Q

How do CFC’s damage the ozone layer? (2)

A

They are unreactive and so difficult to break down. However, once they reach the stratosphere they are broken down by ultraviolet radiation

25
Q

Initiation step to explain how chlorine atoms catalyse decomposition of ozone (1)

A

CFCl3 –> Cl. + .ClFCl2

26
Q

Propagation step to explain how chlorine atoms catalyse decomposition of ozone (2)

A

Cl. + O3 –> ClO. + O2
ClO. + O3 –> Cl. + 2O2

27
Q

Termination step to explain how chlorine atoms catalyse decomposition of ozone (1)

A

Cl. + Cl. –> Cl2

28
Q

What does a chlorine radical act as in the decomposition of ozone? (1)

A

Catalyst

29
Q

What are the alternatives to CFC’s? (2)

A

Hydrofluorocarbons
Hydrochlorofluorocarbons

30
Q

What are the alternatives to CFC’s used for? (3)

A

Refrigerants
Propellants
Dry cleaning industry

31
Q

Where are chlorine atoms formed? (1)

A

In the upper atmosphere when ultraviolet radiation causes the C-Cl bonds in CFC’s to break

32
Q

What do chlorine atoms catalyse and contribute to? (2)

A

Catalyse the decomposition of ozone and contribute to the hole in the ozone layer

33
Q

Uses of haloalkanes (3)

A

refrigerants
solvents
pharmaceuticals

34
Q

Write an overall equation to represent the decomposition of ozone into oxygen (1)

A

2O3 –> 3O2

Chemistry (28 decks)

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