The method and the results are on the amines and polymers lab. Do the analysis yourself first, then check the answers below.
Quick answer: Amines are organic bases because the lone pair on nitrogen accepts a proton, and amino acids contain both an amine and an acid group so they form zwitterions. These answers go with the Chemistry 11-12 lab on amines and polymers: the graph, the calculations, the uncertainties and the conclusion explained, for all 7 analysis questions.
These model answers use the sample results from the lab. Your own Rf values will vary slightly with temperature and solvent mix, so compare patterns and ordering as well as the numbers.
Level: Chemistry grades 11-12 (A Level · IB · Class 11-12) · Curriculum: A Level 3.3.11-3.3.13
Rf = 4.6 ÷ 12.0 = 0.383 and 8.8 ÷ 12.0 = 0.733. Results: 0.38 and 0.73.
Question 2 Identify X
The values match alanine (0.38) and leucine (0.73), and the spots lie level with the known samples. X contains alanine and leucine.
Question 3 Pencil and ninhydrin
Pencil graphite is insoluble and does not move with the solvent; ink would dissolve and run. Amino acids are colourless, and ninhydrin reacts with them to give purple spots that can be seen.
Question 4 Solvent level
If the baseline were under the solvent, the samples would dissolve into the tank and could not be separated as they travel up the paper.
Question 5 Why Rf varies
Rf depends on temperature and solvent composition (also paper type). Running known samples on the same sheet at the same time reduces the effect.
Question 6 A close pair
Rf = 3.3 ÷ 12.0 = 0.28. This differs from glycine (0.26) by only 0.02, so the two spots could easily be confused.
Question 7 Improve the lab
Run a second solvent and compare Rf values, or use two-way chromatography; repeat the run and average the distances; use a larger paper so spots separate further. A second solvent system is the most useful.
