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My AS Level Chemistry - OCR A > 4.2 - Alcohols and Haloalkanes(and more...) > Flashcards

4.2 - Alcohols and Haloalkanes(and more...) Flashcards

1
Q

Why are alcohols polar molecules?

A

Alcohols have a polar -OH bond because of the difference in electronegativity of oxygen and hydrogen atoms
Alcohols are therefore polar

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2
Q

Properties of alcohols

A
  • Low volatility
  • High BP
  • Very soluble in water
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3
Q

Why alcohols have high BP/low volatility?

A
  • Alcohols contain weak London Forces and also contain hydrogen bonding.
  • these hydrogen bonds between molecules require more energy to overcome than London forces
  • so more energy required to heat liquid alcohol into a gas
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4
Q

Why alcohols are soluble in water

A

-Alcohols form hydrogen bonds with water molecules between -O on water and -Oh group on alcohols

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5
Q

Trend in solubility and Volatility with increasing hydrocarbon chain length

A

-Volatility: Volatility decreases
More energy required to break increased London Forces and strong hydrogen bonds in -OH group
-Solubility: decreases with increased hydrocarbon chain length
-OH group has less influence on whole molecule as CH chain increases

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6
Q

What are primary alcohols?

A

When -OH group bonded to a carbon bonded to 1 other carbon

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7
Q

What are secondary alcohols?

A

When -OH group bonded to a carbon that is bonded to two other carbons

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8
Q

What is a tertiary alcohol?

A

-OH group is bonded to a carbon bonded to three other carbons

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9
Q

Which alcohols oxidise?

A

Primary - yes
Secondary - yes
Tertiary - no

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10
Q

What do primary and secondary alcohols oxidise to?

- What conditions required?

A

Primary:
Heat gently and with Distillation - aldehyde

Heat strongly under Reflux with excess H+/pot di - carboxylic acid

Secondary:
Heat strongly under Reflux with excess H+/pot di - ketone

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11
Q

Reagent and colour change observed during alcohol oxidation

A

Acidified potassium dichromate -
H+/Cr2O72-

Orange to green

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12
Q

Reason for different conditions of alcohol oxidation

A

Primary alcohol:
Distillation - aldehyde has lower BP than Carboxylic acid.
- need to distil out aldehyde before complete oxidation completed to produce any carboxylic acid
Prevents any further reaction with oxidising agent

Reflux - excess H+/pot di used to completely oxidised all alcohol to a carboxylic acid
Any aldehyde formed also undergoes oxidation to carboxylic acid

Secondary alcohol:
Reflux - ensures reaction goes to completion and that all alcohol is oxidised completely to a ketone

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13
Q

Dehydration of alcohols process

A
  • Water molecule removed from alcohol
  • C-C bond concerned turns into C=C double bond
  • catalyst used is either sulfuric acid(H2SO4) or phosphoric acid(H2PO4)
  • produces an alkene and a water molecule
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14
Q

Substitution reaction of alcohols process

A
  • Alcohols react with hydrogen halides to form haloalkanes
  • Alcohol heated under reflux with sulfuric acid and a sodium halide
  • Hydrogen halide forms and reacts with alcohol to produce the haloalkane
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15
Q

Why haloalkanes are polar

A
  • They have a carbon-halogen bond in their structure
  • halogens are more electronegative than carbon atoms
  • Electron pair in carbon-halogen bond is therefore closer to the halogen atom than the carbon atom.
  • So the carbon-halogen bond is polar
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16
Q

Nucleophile def

A

An electron pair donor

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17
Q

Examples of nucleophiles

18
Q

How does nucleophilic substitution occur?

A
  • Occurs in primary haloalkanes

- Nucleophile replaces the halogen in the carbon-halogen bond

19
Q

Process of hydrolysis reaction of haloalkanes

A
  1. The nucleophile, OH- approaches the carbon atom attached to the halogen on the opposite side of the molecule from the halogen atom
  2. This direction of attack by the OH- minimises repulsion between the nucleophile and the (delta negative) halogen atom
  3. A lone pair of electrons on the hydroxide ion is attracted and donated to the (S+)carbon atom.
  4. A new bond is formed between the oxygen atom of the hydroxide ion and the carbon atom
  5. The carbon-halogen bond breaks by heterolytic fission
  6. The new organic product is an alcohol. A halide ion is also formed

Aqueous sodium hydroxide is used to convert haloalkanes to alcohols
Heated under reflux to obtain good yield of product, as reaction at room temp is quite slow

20
Q

Strongest to weakest halogen-carbon bond

How fast do each bonds react

A 
Strongest:
C-F
C-Cl
C-Br
C-I
Weakest

Bond strength decreases down the group

Weakest carbon-halogen bond will be broken the quickest

21
Q

Reason for strength of carbon-halogen bonds down the group

A

Decreases down the group as the atomic radii increase, so the nuclei of the atoms in a covalent bond get further apart

22
Q

Hydrolysis of primary haloalkanes

A
  • Carry out the reaction in the presence of aqueous silver nitrate
  • Water acts as a nucleophile, present in the aqueous silver nitrate
  • 1 iodi-butane will hydrolyse the quickest and 1 chloro-butane will hydrolyse the slowest due to the strength of the relative bonds
23
Q

Uses of CFCs

A
  • Refrigerators
  • Aerosol propellants
  • Air conditioning units
24
Q

Properties of CFCs

A
  • Stable
  • Inflammable
  • Volatile/low BP so is gas at room temp
  • non-toxic
25
CFC radical substitution of ozone layer process
Initiation: CF2Cl2 —> CF2Cl. + Cl. Propagation: Step 1: Cl. + O3 —> ClO. + O2 Step 2: ClO. + O —> Cl. + O2 Overall: O3 + O —> 2O2
26
How CFCs affect ozone layer
- They break down the ozone layer - The C-Cl bond breaks near the stratosphere and produces Cl radicals which cause the radical substitution or breakdown of the ozone layer, O3
27
Breakdown of ozone with nitrogen oxide radials process
Nitrogen oxide radical formed during lightning strikes Propagation: Step 1: NO. + O3 —> NO2. + O2 Step 2: NO2. + O —> NO. + O2 Overall: O3 + O —> O2
28
Heating under reflux info.
-Heating mantle used to heat flammable liquids so that no naked flames are present -add anti-bumping granules - contents will boil smoothly -heating under reflux enables a liquid to be continually boiled/oxidised whilst reaction takes place. This prevents volatile components escaping the flask and boiling dry/evaporating
29
Distillation info.
- Chemical reaction may not go to completion, or by-products could form as well as desired product - helps separate a pure liquid from its impurities - gently heat flask - liquid in mixture with lowest BP will evaporate and boil first. It reaches the condenser and condenses into a liquid, drips into a flask
30
Purifying organic products info.
-
31
Common drying agents
``` These remove any water in the mixture or product Common drying agents include: -anhydrous calcium chloride -anhydrous calcium sulfate -anhydrous magnesium sulfate ```
32
Why redistillation is performed | Process of redistillation
- If organic products have BPs that are relatively close together, the prepared sample may still have some impurities. - Distillation apparatus is cleaned, dried and set up again for second distillation - this time only collect the product with the BP of the compound you are trying to make. - The narrower the boiling range the purer the product - you will now have separated your product from any impurities
33
Different functional groups to know
``` Alcohol: -OH Alkene: -C=C Carboxylic acid: -COOH Haloalkane: X-C(any halogen bonded to a carbon) Ketone: -C=O Aldehyde: -COH(H-C=O) ```
34
Something to do with synthetic routes
Just learn them on textbook page: | 245
35
Two different analytical techniques
- Mass Spectrometry | - Infrared Spectroscopy
36
Use of mass spectrometry
- Use of the molecular ion peak from a mass spectrum to determine the molecular mass - use of fragment ions to identify sections of a molecule
37
Uses of Infrared Spectroscopy
- Breathalysers(detect alcohol consumption) | - Monitoring air pollution
38
How molecules absorb infrared energy
The bonds vibrate
39
Different greenhouse gases
- Water vapour - CO2 - Methane
40
How the greenhouse effect works
- Some IR radiation passes through the atmosphere and is absorbed on the Earth’s surface - It is then re-emitted from the surface in the form of longer-wavelength IR radiation - greenhouse gases absorb this longer- wavelength IR radiation - their bonds vibrate as the molecule re-emit this energy as radiation that increases the temperature of the atmosphere close to Earth’s surface - this leads to global warming

My AS Level Chemistry - OCR A (14 decks)

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