2019 A Level H2 Chemistry Paper 1 Question 25 - Deduce Major Species for Glutamic Acid at pH 7
Here's 2019 A Level Chemistry Paper 1 Question 25.
We have to deduce the major species for glutamic acid at pH 7.
First we need to deduce the pKa values for the functional groups present in glutamic acid.
alpha acid - pKa 2.1
R group acid - pKa 4.1
alpha amine - pKa 9.5
Next we have to figure out how each of these functional groups would respond at pH 7.
alpha acid - since pH 7 > pKa 2.1, the solution is alkaline with respect to alpha acid, so alpha acid will react with alkaline solution to form -COO- group
R group acid - since pH 7 > pKa 4.1, the solution is alkaline with respect to R group acid, so R group acid will react with alkaline solution to form -COO- group
alpha amine - since pH 7 < pKa 9.5, the solution is acidic with respect to alpha amine, so alpha amine will react with acidic solution to form -NH3+ group
So we can put everything together to deduce the major species at pH 7.
Comparing the options, we can deduce the answer to this question is option B.
Topic: Nitrogen Compounds and Proteins, Organic Chemistry, A Level Chemistry, Singapore
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