Class 11 Chemistry Chapter 8: Organic Chemistry – Some Basic Principles and Techniques case study question with answers
One case-based question of the kind CBSE-pattern school exams ask: a passage, then 3 parts worth 4 marks in all, with the answer and the marking scheme for each. Written from the NCERT chapter.
Show answer
Answer: (b) 0.70
Rf = 5.6/8.0 = 0.70. 1.43 inverts the ratio; 0.25 is Q's value; 0.56 divides by 10 instead of 8.0.
Show answer
Answer: (c) Q is adsorbed more strongly than P, and the extract contains both P and Q
Q moves less, so it is held more strongly by the silica gel; the extract's two spots match P and Q in height.
Answer and marking scheme
Q adsorbs iodine vapour, so its spot shows up brown. A colourless compound that fluoresces can be seen under ultraviolet light (or a suitable reagent can be sprayed on the plate).
- Q adsorbs iodine, giving a brown spot (1)
- UV light for fluorescent compounds, or a spray reagent (1)
Answer and marking scheme
Amino acids are detected by spraying the plate with ninhydrin solution. Q is adsorbed more strongly on the silica gel than P, so it is held back and moves a smaller distance with the eluant, giving a lower Rf.
- spray with ninhydrin solution (1)
- stronger adsorption, smaller distance, lower Rf (1)