This write up illustrate another application of intermolecular forces which will explain why certain molecular substances are able to dissolve in a particular solvent while the other molecular substances are unable to.
The basic tenet of solubility of molecular substance is "likes dissolve likes". In this phrase, it highlights that in order for a molecular substance to dissolve in a particular solvent, the intermolecular forces formed between the solvent molecule and the solute molecule must be stronger than/ or identical the intermolecular forces between solvent molecules only and between solute molecules only.
Thus, it is expected that polar molecular substance dissolves in polar solvents as similar type of intermolecular forces is formed. And for the same reason, non-polar molecular substances dissolve in non-polar solvent.
However, in the case of solubility of substance in water, we need to be abit more careful. A substance can be soluble in water if it can form hydrogen bonding with water. It need not be able to have hydrogen bonding on its own, but it definitely must be able to form hydrogen bonding with water. This is illustrated by the example below.
The basic tenet of solubility of molecular substance is "likes dissolve likes". In this phrase, it highlights that in order for a molecular substance to dissolve in a particular solvent, the intermolecular forces formed between the solvent molecule and the solute molecule must be stronger than/ or identical the intermolecular forces between solvent molecules only and between solute molecules only.
Thus, it is expected that polar molecular substance dissolves in polar solvents as similar type of intermolecular forces is formed. And for the same reason, non-polar molecular substances dissolve in non-polar solvent.
However, in the case of solubility of substance in water, we need to be abit more careful. A substance can be soluble in water if it can form hydrogen bonding with water. It need not be able to have hydrogen bonding on its own, but it definitely must be able to form hydrogen bonding with water. This is illustrated by the example below.
In addition, in order to dissolve in water, some molecular substance may choose to ionise (some examples include HCl). The formation of ion-dipole moment (this is actually interaction between ion and molecular dipole moment) results in the molecular substance to dissolve favourably in water.
The formation of ion-dipole interaction is also the reason the reason to why ionic compounds prefer to dissolve in water than in a solvent which only has pd-pd (e.g. CHCl3). This is because solvents that can form hydrogen bonding forms the strongest ion-dipole interaction as compared to other solvents which can only exhibit pd-pd.
Lastly, a mind map is available to help you summarise this prose. This map will be a useful guide to conceptualising how the intermolecular forces is applied to predict solubility of a molecular solute.
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Article written by Kwok YL 2009.
The formation of ion-dipole interaction is also the reason the reason to why ionic compounds prefer to dissolve in water than in a solvent which only has pd-pd (e.g. CHCl3). This is because solvents that can form hydrogen bonding forms the strongest ion-dipole interaction as compared to other solvents which can only exhibit pd-pd.
Lastly, a mind map is available to help you summarise this prose. This map will be a useful guide to conceptualising how the intermolecular forces is applied to predict solubility of a molecular solute.
-- -- -- -- --
Article written by Kwok YL 2009.
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