Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Chemistry > Chapter 15 > Flashcards

Chapter 15 Flashcards

You may prefer our related Brainscape-certified flashcards:
Periodic Table flashcards Chemistry 101 flashcards AP® Chemistry flashcards Organic Chemistry 101 flashcards
1
Q

What are haloalkanes?

A

Compounds which contain carbon, hydrogen and at least one halogen.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What do you do when naming haloalkanes?

A

A prefix is added to the name of the longest chain to indicate the identity of the halogen. When there is more than one halogen present in the structure they are ordered alphabetically.
F - Fluoro Cl- Chloro Br- Bromo I- Iodo

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Describe the electronegativity of halo alkanes?

A

The halogen atoms are more electronegative than the carbon atoms so the pair of electrons in the bond are closer to the halogen atoms and the carbon atom where this bonds between carbon hydrogen is polar. The carbon atom has a slight positive charge so can attract species containing a lone pair of electrons.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What are nucleophiles?

A

There are spaces which can donate a lone pair of electrons to form a new covalent bond. They are negative ions which are attracted to an electron deficient carbon atom. These include hydroxide ions, water molecules and ammonia molecules.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What happens when a halo alkanes reacts with a nucleophile?

A

The nucleophile replaces the halogen in a substitution reaction. A new compound is produced containing a different functional group. The reaction mechanism is nucleophilic substitution.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What type of halo alkanes undergo nucleophilic substitution?

A

Primary Haloalkanes

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What is hydrolysis ?

A

It is a chemical reaction which involves water or aqueous hydroxide ions which causes the breaking of a bond in a molecule resulting in 2 products.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What does hydrolysis of a haloalkane produce?

A

A compound where the halogen atom is replaced with an OH group to form an alcohol this reaction occurs under reflux.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Describe the mechanism of nucleophilic substitution?

A
  1. The nucleophile OH- approaches the carbon atom attached to the halogen on the opposite side of the molecule from the delta minus halogen atom to minimise repulsion.
  2. A lone pair of electrons on the OH- ion is donated to the delta plus carbon atom. A new bond forms between the oxygen of the OH- and the carbon atom.
  3. The carbon- halogen bond breaks due to heterolytic fission.
  4. The new organic products is an alcohol and a halide ion.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What can halo alkanes be converted using into alcohols?

A

Can you sodium hydroxide which is heated under reflux in order to obtain a good yield.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What does the rate of hydrolysis depend on?

A

The bond strength

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What happens in hydrolysis of haloalkanes?

A

The carbon-halogen bond breaks and the OH group replaces the halogen in the haloalkane.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Which haloalkanes react the fastest?

A

Iodoalkanes react the fastest (C–I bond is the weakest, less energy is required to break the bond)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Which haloalkanes react the slowest?

A

Fluoroalkanes react the slowest (C – F bond is the strongest, more energy is required to break it). With Fluoroalkanes being unreactive.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

In order to state the haloalkanes which reacts the fastest to the slowest?

A

Iodoalkanes, bromoalkanes, chloroalkanes, fluoroalkanes

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What is the general equation for hydrolysis of primary haloalkanes?

A

CH3CH2CH2CH2X +H2O —> CH3CH2CH2CH2OH + H+ + X-

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What do halide ions react with to form a precipitate of silver halide?

A

Silver ions

Ag+ (aq) + X- (aq) –> AgX

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

What is a bridging solvent and why is it used?

A

Approaching solvent allows water and the halo alkanes to mix as halo alkanes are insoluble in water so the reaction is carried out in the presence of an ethanol solvent. The nucleophile is water.

19
Q

Describe the experiment of the hydrolysis of primary haloalkanes?

A
  1. Set up 3 test tubes
    Tube 1: 1 cm³ of ethanol and 2 drops of 1-chlorobutane
    Tube 2: 1 cm³ of ethanol and 2 drops of 1-bromobutane
    Tube 3: 1 cm³ of ethanol and 2 drops of 1-iodobutane
  2. Stand the test tubes in a water bath of 60°C.
  3. Place a test tube of 0.1 moldm³silver nitrate in a water bath and allow all tubes to reach a constant.
  4. Add 1 cm³ of silver nitrate into each test tube and start the timer.
  5. Observe the test tubes for 5 minutes and record the time it takes for precipitates to form.
20
Q

State the results found in the hydrolysis of the primary haloalkanes?

A

1-chlorobutane - white precipitate forms very slowly
1- bromobutane - cream precipitate forms slower than iodo and faster than chloro
1-iodobutane - yellow precipitate forms rapidly

21
Q

Describe the rate of hydrolysis as the carbon halogen bond strength decreases?

A

As the carbon halogen bond strength decreases the rate of hydrolysis increases.

22
Q

Give the uses of organohalogen compounds

A

General solvents, dry cleaning solvents, making polymers, flame retardant, refrigerants.

23
Q

What is the ozone layer?

A

It is found that the outer edge of the stratosphere
(10- 40 km above the Earth surface). Ozone absorbs the biological damaging ultraviolet radiation (UV – B) from the sun rays allowing only a small amount to reach the surface. Continue depletion of the ozone layer will allow more UV-B radiation to reach the surface.

24
Q

What does exposure to UV-B cause?

A

Sunburn, skin cancer and genetic damage.

25
Q

Describe the breakdown of ozone?

A

Initially very high energy UV breaks oxygen molecules into oxygen radicals, O via homolytic fission. A steady state is then set up involving oxygen and oxygen radicals in which ozone is being constantly formed and broken down. In this steady state the rate of those formed is the same as the rate of ozone breakdown.

26
Q

What does UV radiation cause for ozone?

A

In the stratosphere ozone is continually being formed and broken down by the action of UV radiation.

27
Q

What has disrupted the equilibrium of ozone formation and breakdown?

A

Human activity, especially in CFCs.

28
Q

What are CFCs?

A

These are chlorofluorocarbons which contain chlorine, fluorine and carbon. CFCs and HCFCs were the most common compounds found in refrigerants, air-conditioning unit and has aerosol propellants.

29
Q

What did Thomas Midgley discover?

A

That due to the strength of carbon – halogen bonds CFCs are very stable, chemically inert, non-toxic, low flammability.

30
Q

What did Mario Molina and Frank Sherwood Rowland do?

A

They looked into the impact of CFCs on the earths atmosphere. They concluded that CFCs remain stable until they reach the stratosphere where they break down into chlorine radicals.

31
Q

What do chlorine radicals do?

A

They catalyse the breakdown of the ozone layer.

32
Q

What happens when CFCs reach the stratosphere?

A

The UV radiation provides a sufficient amount of energy to break the carbon- halogen bond in CFCs by homolytic fission to form radicals. As C– Cl bond has the lowest enthalpy that bond breaks first (C-F bond is too strong to break).

33
Q

What is the initiation of breakdown due to radiation called?

A

Photodissociation

34
Q

Tell me about the chlorine radical?

A

It is a very reactive intermediate which can react with ozone molecules breaking it down into oxygen. In the second propagation step the chlorine radicals is regenerated as it can then attack and remove another ozone molecules in propagation.

35
Q

How many molecules of ozone can 1 CFC molecule break down?

A

100,000 molecules of ozone

36
Q

Where are nitrogen oxide radicals formed?

A

They are naturally formed during lightning strikes and aircraft travel in the stratosphere. Nitrogen radicals cause a breakdown of ozone in a similar way to chlorine.

37
Q

State the general equation for any radical, X in the stratosphere?

A

X* + O3 —> XO* + O2
XO* + O —> X* + O2
overall equation : O3+O —> 2O2

38
Q

What is the Montréal protocol?

A

It was an agreement to introduce steps of the complete removal of CFCs.

39
Q

What has been developed to remove refrigeration and air-conditioning units?

A

Coolants have been developed using hydrocarbons, ammonia or CO2.

40
Q

What has been used to replace aerosol form products?

A

Pump action spray dispensers have been produced. Where aerosols are still being used the propellant is likely to be a hydrocarbon i.e. butane.

41
Q

What are HFCs?

A

They are hydrofluorocarbons. Which contain no chlorine atoms but are very expensive to manufacture.

42
Q

What a HCFCs?

A

They are hydrochlorofluorocarbons which break down more easily than CFCs as they contain chlorine atoms some could reach the stratosphere. But as they break down more easily than CFCs they’re more likely to break into chlorine radicals before reaching the stratosphere.

43
Q

What are BFRs?

A

These are brominated flame retardant which are organobromine compounds used in the electronics industry for circuit boards, outer coverings and cables to reduce flammability of the product.

Chemistry (23 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions