Q69 · Practice questionSimple familiar4 marks
QUESTION 69 (4 marks)
Glycine has the neutral structural formula .
a) Draw its zwitterionic form in water near its isoelectric point. [2 marks]
b) Draw its predominant form in strongly acidic solution. [1 marks]
c) Explain why a zwitterion has zero net charge but is not uncharged at every site. [1 marks]
WORKED SOLUTION
4 marksPractice marking scheme
Zwitterion ; acidic form .
A proton moves from the carboxyl group to the amine. The positive ammonium and negative carboxylate charges cancel overall. At low pH the carboxylate is protonated.
- Shows NH₃⁺ group. [1 marks]
- Shows COO⁻ group in the zwitterion. [1 marks]
- Shows NH₃⁺ and COOH in acidic form. [1 marks]
- Explains equal opposite charges give zero net charge. [1 marks]
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