6a.) When would you add sand to a chromatography column and why? What other materials could be added to a chromatography column instead of sand and why might they be used?
b.) What three criteria must be met in selecting a suitable solvent to recrystallize a solid sample?
Solution
Answer: 6a In chromatography, we generally have stationary phase (solid support) and mobile phase (liquid or gas). The mobile phase carries the component of a mixture from one side to other thorugh passing the stationary phase.
Silica will act as an adsorbent in chromatography. Due to presence of Si-O bond -OH group at the surface of silica, It is slightly acidic as well as polar which helps in adsorbing of the molecules or components onthe basis of their polarity. Hence the one which is more polar will have polar-polar interactions and will adsorb strongly and the other will pass through by mobile phase.
The other components which can used in place of silica is alumina. This has similar properties such as silica, however the nature (acidic/basic) of adsorbent stationary phase is now different. It can act as a base so it will bind acidic component strongly over less acidic or basic components.
The choice of adsorbent or stationary phase is related to seperation of components present in the mixture.
Acidic or basic, polar or less polar.
We can easily pack the column with desired adsorbent.
b.)
1. It should not dissolves the substance to be purified at room temperature. It means; solute should not have any solubility or very less solubility at room temperature. But it should dissolve the solute at the elevated temperature, such as near to boiling point of solvent.
2. Impurities should dissolve in the solution at room temperature or solvent should not dissolves the impurities even at elevated temperatures
3. Solvent must not react with the substance which is needed to be purify, solvent should not be volatile or very expensive.
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6a-) When would you add sand to a chromatography column and why- What.docx
1. 6a.) When would you add sand to a chromatography column and why? What other materials
could be added to a chromatography column instead of sand and why might they be used?
b.) What three criteria must be met in selecting a suitable solvent to recrystallize a solid sample?
Solution
Answer: 6a In chromatography, we generally have stationary phase (solid support) and mobile
phase (liquid or gas). The mobile phase carries the component of a mixture from one side to
other thorugh passing the stationary phase.
Silica will act as an adsorbent in chromatography. Due to presence of Si-O bond -OH group at
the surface of silica, It is slightly acidic as well as polar which helps in adsorbing of the
molecules or components onthe basis of their polarity. Hence the one which is more polar will
have polar-polar interactions and will adsorb strongly and the other will pass through by mobile
phase.
The other components which can used in place of silica is alumina. This has similar properties
such as silica, however the nature (acidic/basic) of adsorbent stationary phase is now different. It
can act as a base so it will bind acidic component strongly over less acidic or basic components.
The choice of adsorbent or stationary phase is related to seperation of components present in the
mixture.
Acidic or basic, polar or less polar.
We can easily pack the column with desired adsorbent.
b.)
1. It should not dissolves the substance to be purified at room temperature. It means; solute
should not have any solubility or very less solubility at room temperature. But it should dissolve
the solute at the elevated temperature, such as near to boiling point of solvent.
2. Impurities should dissolve in the solution at room temperature or solvent should not dissolves
the impurities even at elevated temperatures
2. 3. Solvent must not react with the substance which is needed to be purify, solvent should not be
volatile or very expensive.
