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Esters
Reactions of Carbon Compounds
| Question | Answer |
|---|---|
| Functional group for esters | COO |
| General formula for ester homologous series | CnH2n+1COOCxH2x+1 |
| carboxylic acid + alcohol --> (conc. H2SO4, heat above arrow) | ester + water |
| What type of reaction is ester formation? | Condensation reaction (also called a dehydration reaction) |
| What are the reaction conditions required for esterification? | Concentration H2SO4, heat |
| Why is concentrated H2SO4 needed? | 1) It acts as a catalyst to speed up the reaction 2) It is a powerful dehydrating agent, removing water produced during the reaction thus favouring the forward reaction and increasing the yield of ester produced. |
| T or F. Esterification is a reversible process. | T |
| How is the formula for an ester written? | acid part first, alcohol part second |
| How is the name of an ester written? | Alcohol part first ending with 'yl' and acid part second ending with 'anoate'. |
| Ethanoic acid + ethanol --> (conc. H2SO4, heat above arrow) | ethyl ethanoate + water |
| CH3COOH (l) + C2H5OH (l) --> (conc. H2SO4, heat above arrow) | CH3COOC2H5 (l) + H20 (l) |
| Name CH3COOC2H5 | ethyl ethanoate |
| CH3COOC3H7 | propyl ethanoate |
| C2H5COOCH3 | methyl propanoate |
| butyl methanoate | HCOOC4H9 |
| ethyl butanoate | C3H7COOC2H5 |
| Why is the condenser placed in a reflux (vertical) position in ester formation? | This is to cause the acid, the alcohol and the ester vapours to condense and return to the flask for further reaction and so no ester is lost. |
| How can a mixture of acid, alcohol and ester be separated? | The acid and the alcohol will dissolve when poured into water but the ester will form an oily layer on top which can be separated. |
| What is the reverse of a condensation reaction? | Hydrolysis |
| What happens during hydrolysis? | Molecules are broken down into smaller ones by reacting with water |
| State the two types of hydrolysis. | 1) Acid hydrolysis 2) Alkaline hydrolysis |
| What are the products of acid hydrolysis of an ester? | carboxylic acid + alcohol |
| CH3COOC2H5 (l) + H20 (l) --> (H+ ions above arrow) | CH3COOH (aq) + C2H5OH (aq) |
| What reaction conditions are required for acid hydrolysis? | 1) Presence of water 2) Acid catalyst e.g. dilute H2SO4 or HCl |
| How many stages are involved in alkaline hydrolysis? | 2 |
| What are the products of the first stage of alkaline hydrolysis? | carboxylic acid and ethanol |
| What are the products of the second stage of alkaline hydrolysis? | salt and water |
| Step 1: Ester + water --> (alkali above arrow) | carboxylic acid + alcohol |
| Step 2: Carboxylic acid + alkali --> | salt + water |
| CH3COOH (aq) + NaOH (aq) --> | CH3COONa (aq) + H2O (l) |
| Overall: Ester + alkali --> | salt + alcohol |
| CH3COOC2H5 (l) + NaOH (aq) --> | CH3COONa (aq) + C2H5OH (aq) |
| What is saponification? | The alkaline hydrolysis of large esters found in animal fats and vegetable oils. It is used in the manufacture of soap. |
| fat or oil + NaOH --> (heat above arrow) | sodium salt of a long chain alkanoic acid + glycerol |
| Another name for glycerol | propane-1,2,3-triol |
| (C17H35COO)3C3H5 (l) (glycerol octadecanoate /a fat) + 3NaOH (aq) --> (heat above arrow) | 3C17H35COONa (aq) (sodium octadecanoate (a soap/sodium salt of long chain acid) + C3H5(OH)3 (aq) (glycerol) |
| What is detergent? | A chemical added to water to remove dirt from clothing, surfaces and floors.It has a hydrophilic head and a hydrophobic tail. Grease and dirt are attracted to the tail and the head is attracted to water which washes the molecules away. |
| What is a soapy detergent? | Simply soap made by reacting fats with alkali (NaOH or KOH) |
| What is a soapless detergent? | Synthetic detergent made from petroleum. |
| What is hard water and soft water? | Hard water contains dissolved Ca2+ and Mg2+ ions. Rain water is hard. Soft water does not contain these dissolved ions. Water can be softened by various processes including chemical treatment and boiling. |
| Distinguish between soapy and soapless detergents' ability to lather in hard water. | Soapy detergents do not lather easily in hard water. They form scum (grey, greasy layer on skin, surfaces etc ) Soaless detergents lather easily with hard water. They do not form scum. |
| Distinguish between soapy and soapless detergents' biodegradabiity. | Soapy detergents are biodegradeable. Some soapless detergents are non-biodegradable. |
| What does 'biodegradable' mean? | The ability to be broken down by bacteria in the environment. Re soap, this is important to prevent foaming in sewerage systems and waterways e.g. lakes and rivers. |
| Distinguish between soapy and soapless detergents' ability to cause eutrophication. | Soapy detergents do not contain phosphates and so not cause pollution. Soapless detergents contain phosphates which pollute aquatic environments and cause eutrophication. |
| What is eutrophication? | Excessive, rapid growth of green algae in waterways which lead to stagnation and hypoxia (depletion of dissolved oxygen for other aquatic organisms) |
| Distinguish between the source of production for soapy and soapless detergents. | Soapy detergents - made from a renewable source. Fats and oils. Soapless detergents - made from non-renewable source i.e. petroleum. |
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CSEC Chemistry 11th Grade
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