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Carboxylic Acids, Their Derivatives and Kc
2017 Paper Two
Looking at past AQA A-level Chemistry questions, I wanted to go beyond the answers and focus on thought processes, ideas and tips that will help in examinations.
The series will help you to spot weaknesses and help with revision, or it can serve as addenda to your notes.If you haven't gone through the paper, please look up the questions at www.aqa.org.uk, or click the direct link below, and have a go...
For the carboxylic acid, 0.470 – 0.180 = 0.29 moles have reacted
From the stoichiometry, this indicates that 0.29 moles of water have been formed
0.29 ÷ 2 = 0.145 moles of the diester are formed at equilibrium
0.205 – 0.145 = 0.06 moles of the diol remain at equilibrium
Straightforward - products on top. reactants on the bottom
Volumes will cancel out
There are the same number of moles on each side of the equation
Steady as we go...
Most marks are lost due to an incorrect rearrangement of the expression. You need to make sure you give your answer to three significant figures. If you manage to write the correct answer, all 3 marks are awarded!
Use moles/volume (marks scheme indicates that the volumes need not be included)
The mark scheme allows 0.789 ± 0.001
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