| Date | May 2014 | Marks available | 1 | Reference code | 14M.3.sl.TZ1.3 |
| Level | SL | Paper | 3 | Time zone | TZ1 |
| Command term | Suggest | Question number | 3 | Adapted from | N/A |
Question
A sample is known to contain three different amino acids. After carrying out paper chromatography using a solvent made up of propan-1-ol, water and ammonia, the following chromatogram was obtained once the spots had been developed with ninhydrin.
Calculate the \({R_{\text{f}}}\) values for the two spots.
Spot 1:
Spot 2:
Suggest a reason why only two spots are present.
Suggest how the chromatography experiment with the same sample could be altered in order to obtain three spots.
Markscheme
Spot 1: \({R_{\text{f}}} = 0.75\) and Spot 2: \({R_{\text{f}}} = 0.25\);
two amino acids have the same \({R_{\text{f}}}\) value;
change the polarity/make-up of the solvent / use a different solvent;
Accept two way (paper) chromatography.
Examiners report
This question was generally well answered. In part (a) some candidates reversed the answers for the spots and lost the mark. Very few linked the \({R_{\text{f}}}\) value in part (b) to the two amino acids on same spot; often the reason stated was that one amino acid did not dissolve. Part (c) was well answered. Students demonstrated a good understanding of how the nature of the solvent affects the \({R_{\text{f}}}\) value.
This question was generally well answered. In part (a) some candidates reversed the answers for the spots and lost the mark. Very few linked the \({R_{\text{f}}}\) value in part (b) to the two amino acids on same spot; often the reason stated was that one amino acid did not dissolve. Part (c) was well answered. Students demonstrated a good understanding of how the nature of the solvent affects the \({R_{\text{f}}}\) value.
This question was generally well answered. In part (a) some candidates reversed the answers for the spots and lost the mark. Very few linked the \({R_{\text{f}}}\) value in part (b) to the two amino acids on same spot; often the reason stated was that one amino acid did not dissolve. Part (c) was well answered. Students demonstrated a good understanding of how the nature of the solvent affects the \({R_{\text{f}}}\) value.
