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A-level Chemistry y1 > 18:Haloalkanes > Flashcards

18:Haloalkanes Flashcards

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1
Q

What is the functional group in haloalkanes

A

The halogen atom (F, Cl, Br or I)

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2
Q

Why are haloalkanes insoluble in water

A

They cannot form hydrogen bonds

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3
Q

Why does the boiling point of a haloalkane increase with the number of carbons

A

Increase in surface contact area between molecules means an increase in induced dipole-dipole forces, so more energy is needed to break them.

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4
Q

Equation for reaction of ethane with bromine

A

CH₃CH₃ + Br₂ → CH₃CH₂Br + HBr

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5
Q

Why is the reaction of an alkane and a halogen a bad way to synthesise haloalkanes

A

because more than one hydrogen atom can be substituted and (in alkanes bigger than ethane) substitution can occur at different positions. Consequently a mixture of products is likely to be formed, with only a low percentage yield of the desired product

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6
Q

What is the name of the mechanism for alkane + halogen

A

Radical substitution

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7
Q

Equation for reaction of ethene with HBr

A

CH₂=CH₂ + HBr → CH₃-CH₂Br

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8
Q

What are the products for alkanes + halogens

A

haloalkane + hydrogen halide

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9
Q

What are the products for alkene + hydrogenhalide

A

haloalkane

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10
Q

What is the name of the mechanism for alkene + hydrogen halide

A

Electrophillic addition

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11
Q

Why is the reaction of an alkene + hydrogenhalide quite an efficient way to synthesise haloalkanes

A

There’s 100% atom economy
Only one hydrogen halide molecule can react with each C=C double bond so in principle there is only 1 or 2 possible products.

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12
Q

How is the major or minor product decided

A

The major product is formed via a more stable carbocation intermediate

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13
Q

Equation for reaction of methanol + HBr

A

CH₃-OH + HBr → CH₃-Br + H₂O

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14
Q

What are the products for the reaction of alcohol + hydrogen halide

A

Haloalkane + H₂O

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15
Q

What are the conditions for the reaction of an alcohol + hydrogen halide to form a haloalkane

A

Warm the alcohol with a mixture of NaBr or NaCl and concentrated H₂SO₄. This mixture generates the HBr in the reaction.

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16
Q

What are the conditions needed for substitution of a halogen atom by -OH to form an alcohol from a haloalkane

A

Heating with aqueous sodium hydroxide

17
Q

What is the name for the mechanism for the substitution of a halogen atom by -OH to form an alcohol from a haloalkane

A

Nucleophilic substitution

18
Q

What is a nucleophile

A

An electron pair donor

19
Q

Equation for substitution of bromine in bromoethane by -OH

A

CH₃CH₂Br + OH¯ → CH₃CH₂OH + Br¯

20
Q

What type of bond fission is in nucleophilic substitution

A

heterolytic fission

21
Q

What is hydrolysis

A

The substitution of a halogen atom by -OH to form an alcohol from a haloalkane

22
Q

How does the rate of hydrolysis change with the different halogens in the haloalkane

A

The rate of reaction increases going down the group.

eg. R-I has a higher rate of reaction than R-F

R represents the rest of the chain.

23
Q

What is added to the haloalkane in the test for rate of hydrolysis

A

Ethanol- as a solvent

Aqueous silver nitrate- to find which halogen is in there

24
Q

What is the method for the test for rate of hydrolysis of haloalkanes

A

To each of the haloalkanes:

  • Add ethanol and silver nitrate.
  • Warm the tubes in the same hot water bath- so all at the same temp.

Observe the rate at which the precipitate appears

25
Q

What reactions occur in test for rate of hydrolysis of haloalkanes

A

-Haloalkane + water
C₂H₅X + H₂O → C₂H₅OH + H† + X¯

-Halide ion + silver ion
Ag†(aq) + X¯(aq) → AgX(s)

26
Q

What are some uses for Chlorofluorocarbons (CFCs)

A

Refrigerants, solvents and aerosol propellants

27
Q

What is the formula for ozone

A

O₃

28
Q

Why is ozone useful

A

it absorbs UV radiation from the sun

29
Q

What is the initiation step for the reaction between CFCs and ozone

A

Forms a chlorine radical
CF₂Cl₂ → CF₂Cl• + Cl•
in the presence of UV light

30
Q

What are the 2 equations to show a chlorine radical reacting with ozone

A

Cl• + O₃ → ClO• + O₂

ClO• + O → Cl• + O₂

Overall: O₃ + O → 2O₂

31
Q

How do the chlorine radicals act as a catalyst in the reaction between chlorine radicals and ozone

A

They are used up and then regenerated, so technically aren’t used up

32
Q

What are the equations to show nitrogen oxide reacting with ozone

A
  • NO + O₃ → •NO₂ + O₂
  • NO₂ + O → •NO + O₂

Overall: O₃ + O → 2O₂

33
Q

How are nitrogen oxides formed at high altitudes.

A

Lightning acting on nitrogen and oxygen in the air.

More NO is formed from the intense heat from jet engines

A-level Chemistry y1 (26 decks)

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