Question

1. If two spots have identical Rf values, does that mean that they are the same identical molecules? Explain why or why not.

2. What value is there in using at least two different solvent systems? How might this be related to question 1.

3. Do some research, and briefly describe the roles of each pigment group in a leaf. Chlorophylls, Carotenes and Anthrocyanins. If the exact function isn’t know, list several of the possibilities.

Answer 1

1.    $R_f=\frac{distance\: moved \:by\: solute}{distance\: moved\: by\: solvent}$

If the Rf value is the same it is possible that the two molecules are identical (not necessarily) because both compound are traveling the same distance in the particular solvent.

They might be a different molecule if the solvent is changed and hence the Rf value will be different.

2. Solvent carries the molecules up the plate, the particular solvent used will have a substantial effect on the retention factor value for the molecules.

The mixture of solvent can also have different effects depending on the proportion of each solvent.

The eluting power of the solvent increases with polarity:

• Non- polar compound move up the plate most rapidly (higher Rf value)
• Polar compound travel the TLC plate slowly (lower Rf value)

3.

PIGMENTS	Role of Pigments in leaf
1. Chlorophylls	Vital for photosynthesis Transform heat energy from sunlight into chemical energy. Used to produce oxygen
2.Carotenes	Protect plant which is overexposed to sunlight Help in photosynthesis by channeling the energy towards chlorophylls
3.Anthrocyanins	Protective role against the extreme temperature. Responsible for the bright colour of fruits and flower