Exam Specification<br />describe the useful chemical and physical properties of esters, such as miscibility, odour and use as a solvent<br />describe the uses of alcohols in the preparation of esters<br />describe the uses of esters in cosmetics and fruit flavourings<br />
What is an ester<br />Esters are produced when an organic acid reacts with an alcohol (you can think of this as neutralisation)<br />Water is made as a by-product of the reaction, just like neutralisation<br />Esters are either natural or man-made<br />Natural esters:<br />Fats and oils: an ester of a fatty acid and glycerol<br />Aromas from fruits like apples, pears, and strawberries are esters<br />Pheromones are natural esters<br />Essential Oils like patchouli and lavender are esters<br />Man-made:<br />Many esters are now manufactured industrially as it is easier than extracting them from plants and animals, e.g. for perfumes and sweets<br />
Esters<br />This one is used in nail varnish remover as it is a good solvent – it dissolves the nail varnish but not your nails<br />
Properties of esters<br />Quite volatile – small esters have lower boiling points than the carboxylic acids <br />This is useful for plants or animals to attract others by scent<br />They aren’t able to take part in hydrogen bonding as well as carboxylic acids<br />This also makes the larger esters very insoluble in water, but more soluble in organic solvents<br />This why they are very useful as solvents for other organic compounds – like the large alcohols were.<br />Very large esters (like oils and fats) have higher boiling points and melting points – remember: a fat is simply a solid oil<br />The larger the ester molecule, the higher the boiling and melting point.<br />
Link to C2 Additional<br />Saturated vs Unsaturated fats<br />Remember – saturated means only single C-C bonds and unsaturated means double C=C bonds.<br />Saturated fats don’t have any kinks, so the chains can line up closely and the have higher melting points (solid at room temperature – fats)<br />Unsaturated fats have kinks in their chains, and so they can’t get very close together and they have lower melting points (liquid at room temperature – oils)<br />
Preparation of Esters<br />Carboxylic Acid + Alcohol Ester + Water<br />Ethanoic acid + ethanol Ethylethanoate + water<br />Methanoic acid + ethanol Ethyl Methanoate + water<br />Often carried out in the presence of an acid catalyst (e.g. conc sulfuric acid) and with gental heating<br />
Making an ester<br />A Pour some boiling water into a 250 cm3 beaker. Leave it to stand.<br />B Put about 2 cm3 of ethanol into a test tube.<br />C Go to the fume cupboard and ask your teacher to add 1 cm3of concentrated ethanoic acid and three drops of concentrated sulphuric acid to your tube.<br />D Stand your tube in the beaker of hot water for about 5 minutes.<br />E While you are waiting, collect a 100 cm3 beaker and fill it about half full with sodium hydrogen carbonate solution.<br />F After 5 minutes, carefully tip the liquid from the test tube into the beaker and stir well.<br />G Carefully smell the product in the beaker.<br />
Questions to practice <br />1. On the Moodle course KS4 Triple Science (Chemistry), at the top under C3 Extension Topic 4 is a worksheet called<br />Fruity Flavours<br />Download it and rearrange the cards.<br />2. Next, download and complete the worksheet called<br />The reactions of Ethanoic Acid Qs<br />This will help you review the last two topics (Acids and Esters)<br />
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