Question
HLPaper 3
The structures of the amino acids cysteine, glutamine and lysine are given in section 33 ofthe data booklet.
1.[1]
An aqueous buffer solution contains both the zwitterion and the anionic forms ofalanine. Draw the zwitterion of alanine.
Verified
Solution
Penalize incorrect bond linkages ormissing hydrogens once only in 8 (a)and 8 (c) (i).
2.[1]
Calculate the pH of a buffer solution which contains 0.700 mol dm–3 of thezwitterion and 0.500 mol dm–3 of the anionic form of alanine.
Alanine p_Ka_ = 9.87.
Verified
Solution
«pH =9.87 + log ( 0.500 0.700 ) »
«= 9.87 – 0.146»
=9.72
pH can be deduced by an alternativemethod.
