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Date May 2017 Marks available 1 Reference code 17M.3.hl.TZ2.8
Level HL Paper 3 Time zone TZ2
Command term Calculate Question number 8 Adapted from N/A

Question

The structures of the amino acids cysteine, glutamine and lysine are given in section 33 of the data booklet.

An aqueous buffer solution contains both the zwitterion and the anionic forms of alanine. Draw the zwitterion of alanine.

[1]
c.i.

Calculate the pH of a buffer solution which contains 0.700 mol dm–3 of the zwitterion and 0.500 mol dm–3 of the anionic form of alanine. 

Alanine pKa = 9.87.

[1]
c.ii.

Markscheme

 

Penalize incorrect bond linkages or missing hydrogens once only in 8 (a) and 8 (c) (i).

[1 mark]

c.i.

«pH = 9.87 + log ( 0.500 0.700 ) »

«= 9.87 – 0.146»

= 9.72

 

pH can be deduced by an alternative method.

[1 mark]

c.ii.

Examiners report

[N/A]
c.i.
[N/A]
c.ii.

Syllabus sections

Options » B: Biochemistry » B.7 Proteins and enzymes (HL only)
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