DP Chemistry (last assessment 2024)
Question 19N.3.sl.TZ0.7b
| Date | November 2019 | Marks available | [Maximum mark: 2] | Reference code | 19N.3.sl.TZ0.7b |
| Level | sl | Paper | 3 | Time zone | TZ0 |
| Command term | Suggest | Question number | b | Adapted from | N/A |
b.
[Maximum mark: 2]
19N.3.sl.TZ0.7b
Aspartame is formed from the two amino acids aspartic acid (Asp) and phenylalanine (Phe).
(b)
The isoelectric point of amino acids is the intermediate pH at which an amino acid is electrically neutral.
Suggest why Asp and Phe have different isoelectric points.
[2]
Markscheme
«Asp isoelectric point lower than Phe and » Phe has a neutral/hydrocarbon side chain ✔
Asp side chain contains −COOH/carboxyl ✔
NOTE: Award [1 max] for “Asp has two carboxyl/−COOH groups and Phe has one carboxyl/−COOH group”.
Accept “Asp has an acidic side chain” for M2
