Chemistry C7
Chemistry C7
4.0 / 5 based on 3 ratings
- Created by: Benjamin Atkinson
- Created on: 15-04-11 11:12
Alkanes
- Chains of carbon atoms surrounded by hydrogen atoms
- Single covalent bonds
- Burn to give carbon dioxide and water
- Don't react with most chemicals (Un-reactive C-C and C-H bonds)
- Low boiling point
- Volatile, gases at room temperature (methane and ethane)
- Do not react with sodium
- Insoluble in water
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Alcohols
- -OH functional group
- Soluble in water
- Good solvent
- Boiling point of 78 degrees - just below water
- Liquid at room temperature - volatile
- Used as solvents (can dissolve lots of compounds water can't)
- Perfumes, aftershaves - methylated spirit (clean paint brushes, fuel)
- Burn in air
- Ethanol reacts with sodium to produce sodium ethoxide + hydrogen
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Carboxylic Acids
- -COOH functional group
- React like other acids - salts formed end in '-anoate'
- Acid + metal -> salt + hydrogen
- Acid + alkali (e.g. magnesium hydroxide) -> salt + water
- Acid + carbonate -> salt + water + carbon dioxide
- Carboxylic acids = weak acids
- Strong tastes and smells (e.g. Vinegar = ethanoic acid)
- ethonol +oxygen -> ethanoic acid + water (oxidation of wine or beer)
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Esters
- Functional group -COO-
- formed from alcohol and carboxylic acid to form ester and water
- Esterification reaction^ - is reversible
- Have pleasant smells, often quite sweet and fruity
- Used in flavourings and aromas
- Volatile - ideal for perfumes (drift to smell receptors in nose)
- Ointments (e.g. Deep Heat smell)
- Solvents for paint, ink, glue, or nail varnish remover
- Plasticisers to make plastics more flexible
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Fats and Oils
- Fats and Oils are esters of glycerol and fatty acids
- Fat and oil molecules mostly consists of fatty acid chains
- Can be saturated (only C-C) or unsaturated (C=C)
- Fat - good for storing energy
- organism can store extra energy as fat to be used later
- ANIMAL FATS - mainly saturated, few C=C bonds, solid at room temp.
- VEGETABLE OILS - mainly unsaturated, lots of C=C bonds, normally liquid at room temp.
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Making an Ester - Refluxing
- Ethyl Ethanoate - ethanol needs to be reacted with ethanoic acid
- Catalyst such as concentrated sulfuric acid can be used to speed things up
- Or heating the mixture - bunsen burner can not be used
- Gently heated mixture in a flask
- Condenser to catch vapours and recycle - giving them time to react - this method is refluxing
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Making an Ester - Distillation
- Needed to seperate ester from other stuff left in the flask (unreacted alcohol and carboxylic acid, sulfuric acid and water)
- Mixture is heated under a fractionating column, as it boils - vapour begins to rise up the fractionating column
- When temperature at top reaches boiling point of ethyl ethanoate - the liquid that flows out of the condenser is collected
- This is impure ethyl ethanoate
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Making an Ester - Purification
- Liquid collected - poured into tap funnel
- Mixture shaken with sodium carbonate solution - removing acidic impurities
- Ester does not mix with water, so mixture seperates into two layers - bottom layer can be tapped off (removed)
- Remaining upper layer is then shaken with concentration calcium chloride solution to remove any ethanol. Lower layer can then be tapped off.
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Making an Ester - Drying
- Remaining water can be removed by shaking with lumps of anhydrous (dry) calcium chloride, which absorbs it - this is called dring
- Finally, the pure ester (pure ethyl ethanoate) can be separated from the solid calcium chloride via filtration
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Exothermic Reaction
- Gives out energy to surroundings (mainly form of heat) and shown by rise in temperature
- Examples inclue fuel burning, and neutrilisation reactions
- In exothermic reactions, the products at at a lower energy than the reactants
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Endothermic Reaction
- Takes in energy from surroundings (mainly form of heat) and shown by fall in temperature
- An example is photosynthesis
- In endothermic reactions the products are at a energy than the reactants
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Activation Energy
- Minimum amount of energy needed for reaction to happen
- If energy input is less than the activation energy there will not be enough energy to start the reaction.
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