Table of Contents
- 1 Why do some substances move farther along the chromatography paper than others?
- 2 Does higher Rf mean more polar?
- 3 Why does Xanthophyll travel the least?
- 4 How would Rf values change if a more polar solvent were used?
- 5 Why do some pigments travel farther in chromatography?
- 6 What happens to pigments when they dissolve in water?
Why do some substances move farther along the chromatography paper than others?
Usually the more soluble a substance is in the solvent, the more rapidly it will move along the paper. Solvents are chosen for the greatest differential solubilities of the substances concerned.
Why do pigments move the farthest?
Carotene moves the farthest because it is the most nonpolar of the pigments and it is attracted more strongly to the acetone-ligroin mixture (mobile phase) than to the paper. This stronger, nonbonded interaction with the mobile phase indicates that carotene is the most nonpolar pigment found in spinach chloroplasts.
What determines how far pigments move on chromatography paper?
The speed at which a particular pigment moves depends on its relative affinities for the two solvent phases; if it has no affinity whatever for the water phase, it will travel at maximum speed, just behind the solvent-front (eg beta-carotene); on the other hand, if the pigment has no affinity whatever for the non-polar …
Does higher Rf mean more polar?
The eluting power of solvents increases with polarity. Non-polar compounds move up the plate most rapidly (higher Rf value), whereas polar substances travel up the TLC plate slowly or not at all (lower Rf value).
Why is TLC more accurate than paper chromatography?
TLC tends to produce more useful chromatograms than paper chromatography, which show greater separation of the components in the mixture – and are therefore easier to analyse. The distance a sample travels can depend on the size or the polarity of the molecules involved.
Which of the pigments is the least polar which is the most?
carotenes
From this, we can deduce that carotenes are the least polar pigments (no polar groups), and xanthophylls are the most polar (two alcohol groups, one at each end of the molecule)….Explanation.
| Pigment | Rf value |
|---|---|
| Chlorophyll a | 0.59 |
| Chlorophyll b | 0.42 |
| Anthocyanins | 0.32-0.62 |
| Xanthophylls | 0.15-0.35 |
Why does Xanthophyll travel the least?
Xanthophyll contains oxygen and does not travel quite as far with the solvent because it is less soluble the beta carotene and forms hydrogen bonds with the paper. Chlorophylls are bound more tightly to the paper than the other two, so they travel the shortest distance.
What is the maximum Rf value for any molecule in paper chromatography?
Size of spot may range 2-5 mm depending upon number of sample to be applied to the paper. The mobile phase which gives Rf value range between 0.2-0.8 are selected for chromatographic work.
How will you use this procedure to identify an unknown type of colored pigment?
Paper chromatography is used as a qualitative analytical chemistry technique for identifying and separating colored mixtures like pigments. It is used in scientific studies to identify unknown organic and inorganic compounds from a mixture.
How would Rf values change if a more polar solvent were used?
In general, how will Rf values change with increasing solvent polarity? Rf values increase with increasing solvent polarity as substance are more attracted to the solvent and therefore move with it.
Is a higher Rf value better?
Non-polar compounds move up the plate most rapidly (higher Rf value), whereas polar substances travel up the TLC plate slowly or not at all (lower Rf value).
What are the disadvantages of chromatography?
Disadvantages Of Column Chromatography –
- It is a time-consuming process for the separation of compounds.
- It is expensive as higher quantities of solvents are required.
- The automated process becomes complicated and therefore costly.
- It has a low separation power.
Why do some pigments travel farther in chromatography?
Others are more attracted to the paper and move more slowly. Usually smaller molecules will move farther than larger ones. Why do colors travel different distances in chromatography? In paper chromatography different pigments can be separated based on their solubility, or their ability to dissolve in water.
Why does ink move up chromatography paper?
Separation of Plant Pigments Using Chromatography. The solvent carries the dissolved pigments as it moves up the paper. The pigments are carried along at different rates because they are not equally soluble. Therefore, the less soluble pigments will move slower up the paper than the more soluble pigments.
How are dyes separated in paper chromatography?
In paper chromatography different pigments can be separated based on their solubility, or their ability to dissolve in water. The more soluble a pigment is, the more readily it will dissolve in the mobile phase and the farther it will usually travel as it is carried by the water being absorbed into the paper.
What happens to pigments when they dissolve in water?
Some pigments dissolve in water easier and are pulled with the water farther up the paper. Others are more attracted to the paper and move more slowly. Usually smaller molecules will move farther than larger ones.