OCR C7 Revision

Alkanes - Alcohols - Carboxylic Acids - Esters - Making Esters.

C7 for OCR 21st Century Science.

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Alkanes

Alkanes are a family of Hydrocarbons. They are made from chains of carbon atoms surrounded by hydrogen atoms.

They only contain single covalent bonds.

1 Carbon Atom = Methane

2 Carbon Atoms = Ethane

3 Carbon Atoms = Propane

4 Carbon Atoms = Butane

alkane + oxygen (plenty) ---> carbon dioxide and water

Alkanes are relatively unreactive towards most chemicals. They don't react with substances dissolved in water. This is because the C-C and C-H bonds are unreactive.

Insoluble in water. Ethane has a boiling point of -103C. Methane and ethane are volatile and are gasses at room temperature.

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Alcohols

Alcohols have an -OH Functional Group on the end of a standard alkane.The first two alcohols are: methanol and ethanol.

Ehtanol has a boiling point of 78C. Therefore it is a liquid at room temperature and evaporates easily making it volatile.

Methanol and Ethanol can dissolve many compounds that water cant. eg: hydrocarbons and oils. It is therefore a very useful solvent. It can also be used to make other organic chemicals.

These factor make it very useful for perfumes

Methylated spirit - is ethanol with chemicals such as methanol added.

Alcohols burn in air because they contain hydrocarbon chains.

Alcohol reacts with sodium: sodium + ethanol ---> sodium ethoxide and hydrogen.

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Carboxylic Acids

Carboxylic Acids have an -COOH Functional Group on the end of a standard alkane. Their names end it (meth) -anoic acid.

Carboxylic acids react like any other acids. They are weak acids and react slowly. The salts fromed in the reaction end in (meth) -anoate.

Carboxylic acids react with metals to give a salt and hydrogen.

Carboxylic acids react with alkails to form salt and water.

Carboxylic acids react with carbonates to give a salt, water and carbon dioxide.

They have strong smells and tastes. If wine is left open in the air for a few days, the ethanol in the wine is oxidised to form ethanoic acid: causing it to taste like vinegar. This is because vinegar is a dilute from of ethanoic acid!

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Esters

Carboxylic Acids have an -COOH- Functional Group on the end of a standard alkane.

alcohol + carboxylic acid <----> ester + water. This is know as esterfication.

They often smell sweet and fruity, and they are also volatile (evaporate easily: makes the smell spread) which makes them ideal for perfumes.

Esters are also used for flavourings, eg: apple, orange, banana etc. They are also used as solvents and plasticisers (make things more flexible)

Fatty Acids are Carboxylic Acids. They often have between 16 and 20 carbon atoms. Fatty acids can be saturated (only C-C single bond) or unsaturated (with C=C double bonds)

Plants and animals often make oils and fats to store energy. When an organism has more energy than it needs it stores some as fat, which they can use later.

Animal Fats: saturated hydrocarbon chains, normaly solid at room temperature.

Vegetable Oils: unsaturated C=C bonds, normaly liquid at room temperature.

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Making Esters

Reflux, Distil, Purify, Dry.

Refer to P.72 of CGP Chemistry Revision Guide.

1 - Refluxing.

To make ethyl ethanoate you need to react ethanol with ethanoic acid. To speed the up the reaction such as a catalyst for example, concentrated sulphuric acid will work. Heating the mixture will also help. This is best done with a condenser which catches any vapour and recycles it - this is called refluxing.

2 - Distillation.

This stage separates the ester from anything else in the flask (eg. unreacted alcohol, carboxylic acid, sulfuric acid and water) The mixture is heated and the vapour goes up a fractionating column. When the top of the column reaches the boiling point of ethyl ethanoate, the liquid that flows out the condenser is impure ethyle ethanoate.

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Making Esters - Continued.

3 - Purification

This stage removes any impurities. Sodium carbonate solution is shaken with the ester to remove any acidic impurities. These two do not mix, so the sodium carbonate can be removed. Then the remaining ester is shaken with concentrated calcium chloride to remove any ethanol. This is then removed. You are then left the the ester (ethyl ethanoate).

4 - Drying

Any water remaining in the ethyl ethanoate can be removed by shaking it with lumps of anhydrous calcium chloride, which absorbs the water.

Finally the pure ethyl ethanoate can be separated from the solid calcium chloride by filtration.

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Comments

Hannah Rose

The information is shown clearly and it's easy to revise from, thankss :]

Bobby

:) that's okay.

JNicole

just printed! thank you :-)

declan

you wrote that carboxylic acids have a -COO functional group under esters and didnt say what the functional group for an ester is.

talha

declan wrote:

you wrote that carboxylic acids have a -COO functional group under esters and didnt say what the functional group for an ester is.

and i quoted this  because im bored and dont wana study :D

emmett

dont carboxylic acids have a COOH group not COO as you stated in the ester section :)

callum W

nice one you condensed 18 houres of lesons in to 30 mins of reading WHY CANT YOU BE A TEACHER

Bobby

emmett wrote:

dont carboxylic acids have a COOH group not COO as you stated in the ester section :)

I wrote these so long ago, and have not idea what a COOH even is anymore, haha, i think i've corrected it? :)

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