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MODULE 2 17 WORKSHEET ESTERS Syllabus reference 9.3.5 Complete the following table. FUNCTIONAL GROUP GENERAL FORMULA INTERMOLECULAR FORCES —OH CnH2n1OH Hydrogen bonding COOH CnH2n1COOH Hydrogen bonding Alcohols Esters �� —C RC—OOR O ���������� == Alkanoic acid — Dispersion � � � � ���� � � � ���� � � � ���� � � � � � � ���� � � ���� � � � � � � ���� � � � ���� � � soluble Ethanol C2H5OH soluble high Ethanoic acid CH3COOH low Methyl ethanoate insoluble CH3—C O O— CH3 � � � � �� � �� � �� �� � � � � � �� � �� � � � � �� � � �� � �� �� �� � � � � �� ��� �������� ����� � �� � � � � � � � � � ��������������� � � �� � � � ���� ���� ������ �� ��������������� � � �� � � � �� �� �� � � � � � �� �������������� � �� �������������� pentanoic acid � � � � ����������� �� �������������� � �� � � � � � ���� ���� �� � � � � � �� ����������� � ���� ���� �� �� �� �������������� �� octanoic acid�� ������������� � � � � � � � � � � � � � � �� �� �� �� � � �� � � �� � � �� � � �� � � �� � � �� � � � � � � � � � � � � � � � � � � �� � � � � � � � � � � � � � � � � � �� � �� ���������������� � � � �� ���������������� � �� � �� � �� � �� � �� � Copyright © 2007 McGraw-Hill Australia � � �� � �� � �� �� CONQUERINGCHEMISTRY HSC MODULE 2 WS 17 � � � � � � � ���� ���� �������� � � � � � � � ����������������� � ���� ���� �������� ���������������� �� � �� � � � �� � �� ������������� � � � � � � � � ������������ ���� �� ������������� � � � � � � � � d EXAMPLE � �� �� ��������� � � � � � � � ���������� ���� �� ��������� � � � � � � � � � c 3-hexanol ��� ����� � ���� � � � ���������� � � � � ���� ���� � ��������� � � � � � � � � � � � ��������� � b � � � ���� � �� � ���� � � 1-propanol � a � 2 high SOLUBILITY IN WATER — O—C �� ���������� � � � �� ���������� � � � ���������� �� ���������� Draw the structures of the compounds: � following � � MELTING/ BOILING POINTS == SERIES � 1 �� ���������������� �� ���������������� �� �� �� �� �� � � �� �� �� � � �� ������������������ �� ������������������ � 1-butyl propanoate �� �� f � � methyl butanoate � � e � � � � � � � � ��� ���� �� ��� ���� �� �� ��� �� ��� � � ��� � ��� �� � ��� � ��� �� �� ���� ���� ���� ��� �� ���� ���� ���� ��� 3 Name the following compounds: a CH3CH2CH2CH2OH 1-butanol b CH3CHCH2CH2CH2CH3 OH 2-hexanol c CH3CH2COOH propanoic acid d CH3CH2CH2CH2COOH pentanoic acid e CH3CH2CH2C—O—CH2CH3 O ethyl butanoate f CH3CH2CH2CH2C—O—CH3 O methyl pentanoate 4 Explain why alcohols and alkanoic acids are soluble in water and esters (except for very simple ones) are not. Alcohols and alkanoic acid have hydrogen bonding but esters have only dispersion forces. Copyright © 2007 McGraw-Hill Australia CONQUERINGCHEMISTRY HSC MODULE 2 WS 17 5 A student was given three containers labelled A, B and C. The student was told they were pentanoic acid, hexane and 1-pentanol but not necessarily in that order. The student tested the boiling point and found the following: Boiling point 138ºC 69ºC 186ºC Container A C B Based on the information provided suggest what was the liquid in the containers, A, B and C. Give reasons for your decisions. strong H bonding B pentanoic acid strongest bonding (Hydrogen bonding) C hexane weak bonding (dispersion) Write balanced equations for the following reactions and name the products of the reaction: �� a ������������������������������������� 1-butanol reacting with ethanoic acid �� ������������������������������������� � � ��� � ��� � � �� �� �� �� � ���� ���� ���� ���� �� ��� ��� ��� ��� �������� ����� ��� ��� ��� ��� �������� ����� ���� 6 A 1-pentanol ��������������� ��������������� b 1-propanol reacting with butanoic acid �� �������������������������������������� �� �������������������������������������� ���� � � ��� ������ � ��� ������ � ��� �� �� ����� ���� ���� �� ��� ��� ��� �������� ��� ��� ����� ��� ��� ��� �������� ��� ��� ����� ���������������� ���������������� 7 8 Three compounds are known to be 1-propanol, ethanoic acid and methyl methanoate. Their boiling points (but not in that order) are 118°C, 32°C and 97°C. Match the correct boiling point to the compound giving reasons for your choice. ethanoic acid 118oC strongest bonding 1-propanol 97oC strong bonding methylmethanoate 32oC weak bonding Describe the process of refluxing and explain why it is necessary for successful esterification. Refluxing is heating a reaction mixture in a vessel with a cooling condenser attached, in order to prevent loss of any volatile production reactant. The reaction mixture needs to be heated to speed up the reaction and refluxing is used to prevent loss of alcohol reactant. Copyright © 2007 McGraw-Hill Australia CONQUERINGCHEMISTRY HSC MODULE 2 WS 17 9 Give two reasons why sulfuric acid is used during esterification refluxing. 1 It is used as a catalyst to speed up the reaction. 2 It absorbs the water that is produced and so forces equilibrium to the right. 10 a Plot the boiling point against number of carbon atoms in the molecule for the esters in the table below. Draw a straight line ruled between the points. ESTER BOILING POINT (°C) ESTER BOILING POINT (°C) methyl methanoate 32 2 butyl ethanoate 126 6 methyl ethanoate 57 3 ethyl butanoate 121 6 methyl propanoate 80 4 ethyl methanoate 54 3 ethyl ethanoate 77 4 ethyl propanoate 99 5 propyl ethanoate 102 5 pentyl ethanoate 148 7 160 140 ���������������� 120 100 80 60 40 20 0 1 2 3 4 5 6 7 ������������������������������� b Use your graph to deduce the way that boiling point depends upon number of carbon atoms in the molecule for esters. The greater number of carbon atoms, the higher the boiling point. c For esters having the same number of carbon atoms in the molecule, does boiling point depend significantly upon the number of carbon atoms in the alkyl group (as opposed to the number in the acyl group—that is, in the ‘anoate’ part of the molecule)? Justify your answer. For esters with the same total number of carbons, where there is more carbons in the alkyl group, the boiling point is higher, e.g. butyl ethanoate > ethyl butanoate. Copyright © 2007 McGraw-Hill Australia CONQUERINGCHEMISTRY HSC MODULE 2 WS 17 11 A student wanted to prepare the insoluble ester, butyl methanoate. a What reagents would the student need to prepare this ester? 1-butanol, methanoic acid and sulfuric acid catalyst b The student used the following experimental set-up. Label the arrowed pieces of equipment. ������������������ cooling water out ������������ ��������� cooling water in ����������������� ����� reaction mixture ���������������� c Describe how the student would extract the ester from the reaction mixture. After heating, pour the contents of the flask into a separating funnel containing 10−15 ml water. Stopper and shake funnel, allow layers to separate and discard aqueous layer. Add solution of 1 mol/L Na2CO3. Shake, drain and discard lower layer, leaving the ester in the funnel. 12 Complete the following table. MAIN ESTER PRESENT FLAVOUR Methyl butanoate apple Octyl ethanoate orange Ethyl methanoate grape Butyl ethanoate raspberry 13 Describe the occurrence, production and use of one ester. Ethyl ethanoate is used as a solvent, and is manufactured on a large scale from acetic acid and ethanol. Copyright © 2007 McGraw-Hill Australia CONQUERINGCHEMISTRY HSC MODULE 2 WS 17