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Chemistry > Alcohols and haloalkanes > Flashcards

Alcohols and haloalkanes Flashcards

1
Q

What is the formula of alcohols?

A

CnH2n+1OH
Suffix is -ol.

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2
Q

What is the polarity of alcohols?

A

Generally polar due to the electronegative hydroxyl group, which pulls electrons away from the C in the C-OH bond.
The hydroxyl group is also polar.

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3
Q

What is the bonding of alcohols?

A

The partial positive charge on hydrogen in OH attracts lone pairs from oxygen on other molecules, forming hydrogen bonds.
There are weak intermolecular induced dipole dipole interactions.

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4
Q

What is the solubility of alcohols?

A

Small alcohols (up to C4H10) form hydrogen bonds with water, so are soluble.
In larger, most of the molecule is non-polar, so there’s less attraction for polar water.
So as they increase in size, solubility decreases.

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5
Q

What is the reactivity of alcohols?

A

Alcohols form hydrogen bonds with each other.
Very strong, so low volatility and high boiling points.

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6
Q

What is substitution reaction of alcohols?

A

Alcohols react with halide ion compounds (NaBr).
The hydroxyl is replaced by the halide, so the alcohol is transformed into a haloalkane, and forms NaHSO4 + H2O.
The reaction requires an acid catalyst - H2SO4.

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7
Q

What is elimination reactions of alcohols?

A

The useful alkenes can be made by eliminating water from alcohols.
Uses an acid catalyst - concentrated H2SO4 or H3PO4, and heated under reflux.
Sometimes called dehydration as it removes water.

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8
Q

What are the products of elimination?

A

The water molecule forms from the hydroxyl group and a hydrogen from a carbon.
So there’s often two possible alkene product, depending on the side of the hydroxyl group the hydrogen is eliminated.
Sometimes the product has E/Z isomers.

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9
Q

What is combustion of alcohols?

A

Oxidise by burning them, produces carbon dioxide and water.

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10
Q

What is combustion of alcohols by acid?

A

Use the oxidising agent acidified potassium dichromate (VI) (K2Cr2O7) (use H2SO4 to acidify).
Primary alcohols are oxidised to aldehydes, then to carboxylic acids.
Secondary to ketones only.
Tertiary cannot be oxidised.

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11
Q

What is the observation of oxidation reactions of alcohols?

A

The orange dichromate ion is reduced to the green chromium (III) ion (Cr3+).
This can be used to test between tertiary and primary/secondary alcohols.

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12
Q

What are aldehydes, ketones, and carboxylic acids?

A

All have the general formula CnH2nO.
Aldehydes are =O and always on carbon 1, -al.
Ketones are =O and are not on the end carbon -one.
Carboxylic acids have a COOH group at the end chain.

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13
Q

What is oxidising primary alcohols to carboxylic acids?

A

Alcohol is mixed with [O] and heated under reflux.
This can increase the temperature of an organic reaction to boiling without losing volatile solvents, reactants or products.

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14
Q

What is oxidising primary alcohols to aldehydes?

A

Gently heating excess alcohol with a controlled amount of [O] in distillation.
This means the aldehyde (with a lower boiling point than alcohol) is distilled off immediately.

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15
Q

What is oxidation of secondary alcohols?

A

Reflux with acidified potassium dichromate (VI) produces a ketone.

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16
Q

What is oxidation of tertiary alcohols?

A

Tertiary don’t react with [O] so only oxidised by burning them.

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17
Q

What is the flammability of alcohols?

A

Flammability decreases as the chain gets longer, because there’s more bonds to break.
Ethanol is added to petrol.

18
Q

What is volatility of alcohols?

A

How easily a substance evaporates.
Alcohols are used in perfumes because of their perfect volatility.

19
Q

What are haloalkanes?

A

An alkane with at least one halogen atom in place of a hydrogen atom.
Prefixes (e.g. bromo-) are placed in alphabetical order.

20
Q

What is the polarity of haloalkanes?

A

Halogens are more electronegative than carbon, so this bond is polar.
The S+ carbon is electron deficient so can be attacked by a nucleophile.

21
Q

What is a nucleophile?

A

An electron pair donor - to somewhere with not enough electrons.
e.g. :OH-, H2O:, :NH3

22
Q

What is a nucleophilic substitution reaction of haloalkanes?

A

A nucleophile attacks a polar molecule, removes the functional group, and attaches where it was.

23
Q

What is hydrolysis of haloalkanes by alkali?

A

Haloalkanes are hydrolysed by warm aqueous alkali (NaOH or KOH) by nucleophilic substitution reaction.
Forms an alcohol and NaX.

24
Q

What is hydrolysis of haloalkanes with water?

A

Water is a weak nucleophile so in a much slower reaction will substitute the halogen.
An alcohol is produced again.

25
Q

What is bond enthalpy in hydrolysis?

A

Weaker carbon-halogen bonds break easier so react faster.
C-F -> C-Cl -> C-Br -> C-I

26
Q

How do you compare hydrolysis rates of haloalkanes?

A

Add silver nitrate to the mixture, a silver halide precipitate forms.
Time how long it takes for each haloalkane in ethanol to precipitate.
Use paper with a black cross underneath to know when it’s formed.

27
Q

What are chlorofluorocarbons?

A

Contain only chlorine, fluorine and carbon.
Very stable, volatile, non-flammable and non-toxic.
Previously used in fridges, aerosol cans, dry cleaning and air-conditioning, until scientists realised it destroyed the ozone layer.

28
Q

What is the ozone layer?

A

A layer of the atmosphere called the stratosphere.
Contains O3.
Absorbs ultraviolet radiation which can cause sunburn or skin cancer.

29
Q

What is the process of natural ozone formation?

A

O2 + UV –> O + O free radicals
O2 + O –> O3

30
Q

What is the thinning of the ozone layer?

A

1970s and 80s, scientists discovered the ozone above Antarctica and Artic was thinning very rapidly.
These holes allow more harmful UV radiation to reach the earth.
These are formed when CFCs travel up into the upper atmosphere and absorb high-energy UV radiation.

31
Q

What is the process of ozone thinning?

A

Initiation: CF2Cl2 + uv –> CF2Cl* + Cl*
Propogation: Cl* + O3 –> O2 + ClO*
ClO* + O* -> O2 + Cl* this is regenerated and attacks another ozone molecule.
O3+O –> 2O2 overall reaction

32
Q

What are nitrogen oxides?

A

NO* from nitrogen oxides destroy ozone too.
Nitrogen oxides form from aircraft engines, and thunderstorms.

33
Q

How do nitrogen oxides destroy ozone?

A

NO* + O3 –> NO2* + O2
NO2* + O –> NO* + O2

34
Q

What is the Montreal Protocol 1987?

A

An international treaty to phase out CFCs and other damaging haloalkanes by the year 2000.
They are only allowed in medical inhalers and fire extinguishers for submarines.

35
Q

What are alternatives to CFCs?

A

HCFCs - hydrochlorofluorocarbons, and HCFs - hydrofluorocarbons are temporary alternatives until safer products are developed.
CFCs takes around 90 years to leave the atmosphere.
HCFCs take 10-20 years which still damage ozone, but the effect is less.
HFCs don’t affect ozone.

36
Q

What are HFCs with greenhouse gases?

A

They contribute to the warming of the earth.
Some hydrocarbons are used in fridges, but are still greenhouse gases.
Most aerosols have been replaced by pump spray systems or nitrogen.
Many industrial fridge and freezers use ammonia.
Carbon dioxide is now used as expanded polymers.

37
Q

What is the greenhouse effect?

A

The earth re-emits any electromagnetic radiation from the sun as infrared radiation (heat).
Various gases in the troposphere absorb some and re-emit in all directions, keeping the earth warm.

38
Q

What are greenhouse gases?

A

Water vapour, carbon dioxide, methane.
The C=O, O-H and C-H bonds absorb infrared radiation, which makes the bonds vibrate more.
This extra energy is passed on to other molecules by collisions, raising kinetic energy and therefore overall temperature.

39
Q

What is global warming?

A

Burning fossil fuels, releasing tonnes of carbon dioxide and chopping down trees used for photosynthesis.
Methane levels have risen as food growth increases.
Cows produce large amounts of methane.
Paddy fields where rice is grown also.
All this rises greenhouse gas concentrations, so more heat is trapped and the earth is warmer.

40
Q

What are the consequences of global warming?

A

Warmer oceans will expand and massive ice sheets could melt, causing sea levels to rise and increase flooding.
The climate depends on a complicated system of ocean currents, winds.
More heat in this system means stormier, less predictable weather.
So there could be less rainfall, with droughts, crop failure, causing famine.
Increased rainfall and flooding could bring diseases like cholera.

Chemistry (26 decks)

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