55-237 Study Guide - Midterm Guide: Glutamine, Acid Dissociation Constant, PhenylalanineExam
SchoolUniversity of Windsor
Course CodeBIOL 2070
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03-59-261 – Organic Chemistry of Biomolecules
Term Test #1
Student #: ______________________________
PLEASE ANSWER ALL QUESTIONS
Duration of the test = 80 min.
Please Note: Tests written in PENCIL can’t be returned for re-marking.
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Question 1 A mixture of [HA] = 0.05 M and [A-] = 0.01 M of an unknown amino acid had a
pH of 7.5.
i) Identify the amino acid.
pH = pKa + log([A-]/[HA]) [1 mark]
7.5 = pKa + log(0.01/0.05) [1 mark]
pKa = 7.5 + 0.7 = 8.2 [1 mark]
The amino acid is cysteine [1 mark]
ii) What would the pH of this solution be upon addition of 0.03 M NaOH?
pH = 8.2 + log([0.01+0.03]/[0.05-0.03]) [2 marks]
pH = 8.2 + 0.3 = 8.5 [2 marks]
Note: if the students calculate the incorrect pKa in (i), they can still get full marks
for (ii) if they do everything else correctly here.
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