assuming that either solvent is otherwise acceptable in a given instance, what a
ID: 489113 • Letter: A
Question
assuming that either solvent is otherwise acceptable in a given instance, what advantages does ethanol have over 1-octanol (CH3CH2CH2CH2CH2CH2CH2CH2OH) asa recrystallization solvent? Hexane over Pentane? water over methanol? assuming that either solvent is otherwise acceptable in a given instance, what advantages does ethanol have over 1-octanol (CH3CH2CH2CH2CH2CH2CH2CH2OH) asa recrystallization solvent? Hexane over Pentane? water over methanol? assuming that either solvent is otherwise acceptable in a given instance, what advantages does ethanol have over 1-octanol (CH3CH2CH2CH2CH2CH2CH2CH2OH) asa recrystallization solvent? Hexane over Pentane? water over methanol?Explanation / Answer
If the compound is crystalline solid, only then the compound can be crystallized. The process of crystallization occurs, when the molecules of the given compound interacts with the neighbouring similar molecules, thus forming a crystal lattice. Now coming to the choice of solvent for crystallization.
1) ethanol vs octanol -
(a) Octanol is non-polar or lipophilic in nature due to long alkyl chain whereas Ethanol is the most Polar compound. As Like dissolves like, Polar compounds gets dissolved in Polar solvent (Ethanol) and non-polar compounds dissolves in Non-poar solvent (Octanol). Therefore, due to polar nature of Ethanol, Polar compounds are easily dissolved in it, which is not the case in Non-polar solvents like Octanol
(b) The solvent has to be evaporated once the compund is dissolved in the solvent. As octanol has high boiling point (195 degrees Celsius), it is very difficult to evaporate the solvent under room temperature (Ethanol boiling point is 78.34 degrees celsius).
Therefore, due to the above reasons, Ethanol is more preferred over octanol for recrystallization.
2) hexane over pentane -
These two solvents are non-polar in nature. Pentane is five carbon chain length hydrocarbon with boiling point of 36.1 degrees C. But, Hexane is six carbon chain length hydrocarbon with boiling point around 69 degrees Celsius. The major principle in crystallization is the slow evaporation of the solvent which occurs with the high boiling point solvent, which in this case is Hexane. Therefore, Hexane is more preferred over Petane.
3) water over methanol
Water is more polar than methanol and most preferred over methanol. Due to more polar character of water it can dissolve highly polar compounds. Water is nontoxic when compared to Methanol. Water has more boiling point(100 degrees celsius) than Methanol (64.7 degrees Celsius). The major principle in crystallization is the slow evaporation of the solvent which occurs with the high boiling point solvent, which in this case is Water. Therefore Water is preferred.
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