ALCOHOLS

  • Created by: Chloe
  • Created on: 11-03-17 10:58
What is nomenclature?
It is the process of naming molecules.
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What is the formula for a titration?
Moles = Concentration x Volume
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What is an acid?
A substance which when dissolved in solution releases H+ ions. Strong acids easily dissociate in solution meaning most H+ ions are released. Whereas a weak acid only partially dissociates. Acids have a pH ranging between 1 and 6.
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What is an alkali?
An alkali is a substance which releases OH- ions when dissolved in solution. It has a pH ranging between 8 and 14.
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What are alcohols?
They have a polar O-H bond. This is due to the large difference in electronegativity between oxygen and hydrogen atoms. This means that alcohols are overall polar. They contain very weak London forces but they do contain strong hydrogen bonds.
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Properties of alcohols.
They have a relatively low volatility due to their ability to form hydrogen bonds between alcohol molecules. This means that they burn easily.
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Alcohol production
There are three methods of producing alcohols: fermentation, hydration and nucleophilic substitution.
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Hydration of alkenes
Conditions required are: 300 degrees celsius and 60 atmospheres. One of the major advantages is that the product produced is pure meaning no further reactions are required. However the disadvantages are: high temperature is required, non-renewable.
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Fermentation
Yeast is required as a catalyst and a temperature between 35 and 55. Advantages: Little energy needed, renewable. However: its slow, and the product is impure.
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Nucleophilic substitution
Haloalkanes are reacted with nucleophiles in a substitution reaction. Dilute sodium hydroxide required so OH- can be used as a nucleophile. The polar bond between the carbon and halide is broken. Slower reaction than reflux.
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Cyanide
Cyanide, either potassium or sodium can be used to release Cn- to act as a nucleophile.
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Ammonia
Excess ammonia can be used as a nucleophile
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What is a nucleophile?
It is an electron donator.
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Water solubility of alcohols.
The first three alcohols dissolve easily in water because they form hydrogen bonds with water. Whereas the longer the chain, the less soluble they are.
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Alcohol uses.
Ethanol is the only alcohol which can be used in alcoholic drinks. Ethanol can be used as a solvent in methylated spirits. Methanol is used as an additive to petrol to improve combustion.
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Primary alcohol
It is one where the carbon attached to the -OH group is also bonded to two other hydrogen atoms. They completely oxidise by reflux to form a carboxylic acid. They partially oxidise by distillation to form an aldehyde.
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Primary alcohol colour change
Changes from orange to green. Potassium dichromate and warm dilute sulphuric acid are added before the oxidation reaction. The colour changes from orange to green.
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Secondary alcohol
The carbon attached to the -OH group is only bonded to one hydrogen atom. They oxidise in a reflux reaction to form a ketone.
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Secondary alcohol colour change
Potassium dichromate and warm dilute sulphuric acid are added before the oxidation reaction. The colour changes from orange to green.
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Tertiary alcohols.
The carbon atom attached to the -OH group is not bonded to any hydrogen atoms. They do not oxidise because of this. Therefore upon the addition of potassium dichromate and dilute sulphuric acid, no colour change and the solution remains orange.
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Aldehydes
Always have -al at the end of their name. C=O bond is always on first carbon so no number needed. Formed by the partial oxidation of a primary alcohol in a distillation reaction. Functional group is -CHO.
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Ketone
Product of the oxidation of a secondary alcohol during a reflux reaction. End in -one. Can't oxidise further. The functional group is -CO, a carbonyl group.
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Carboxylic acid
Product of the complete oxidation of a primary alcohol in a reflux reaction. Functional group is -COOH.
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Products from alcohols
Alkenes can be produced. This is done by dehydration (the removal of a water molecule). Reagents required are concentrated sulphuric acid or phosphoric acid. Reagents are warmed under reflux. Reagents act as a catalyst. It is an elimination reaction.
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Haloalkane
Reflux is required. Alcohol heated under reflux with sulphuric acid and a sodium halide salt.
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Fehlings test
Method of distinguishing between a ketone and an aldehyde. Ketone remains blue with reagent whereas an aldehyde reacts and turns brick red.
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Tollens test
Also called the silver mirror test. Again used to distinguish between a ketone and an aldehyde. Ketones do not react with tollens. However since aldehydes can react further, they form a silver mirror layer with tollens.
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Reflux
The repeated process of evaporation and condensation. Top must not be sealed otherwise the gas pressure builds up and explode. Anti-bumping granules are used to prevent vigorous bubbling. Water goes in at the bottom, out at the top (against gravity).
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Distillation
Used as a separation technique. Distillate needs to be collected in a certain temperature range. Liebig condenser is one of the main pieces of equipment. Liebig condenser goes against gravity to allow efficient cooling and prevent water back flow.
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Purification method
1. Distillation. 2. Separating funnel. 3. Anhydrous (drying) salt. 4. Distillation (again).
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CFCs
Chlorofluorocarbons. Developed for use in aerosols, refrigerants and in air-conditioning. They were used due to their low volatility, reactivity and non-toxicity.
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Problems with CFCs
Many were banned due to their toxicity and effects on the ozone layer. If we had alternatives, CFCs were banned from use in 1987. This was called the Montreal agreement. Hydrofluorocarbons are now being used instead.
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Ozone
O3 is constantly being formed in the upper atmosphere. UV light breaks the bond in oxygen molecules forming free radicals. The oxygen free radical reacts with an oxygen molecule forming an O3 molecule. This reaction is reversible.
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Benefit of ozone
Absorbs UV light allowing life to survive. UV light can cause cancer.
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CFCs and NOx
Radicals from CFCs and NOx from thunderstorms and aeroplanes have been catalysing the real of ozone.
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Chlorine radicals
Breaking down ozone layer. Provide an alternate route which has a lower activation energy. This is creating a hole in the ozone layer.
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