Do polar solutes dissolve easily in water?

1 Answer
Jul 31, 2017


Generally speaking, yes.


"Likes dissolve likes" as the expression goes. Water, a polar solvent, can dissolve polar solutes easily. Ionic compounds and most polar molecules will dissolve in water.

Polar solutes that contain N-H and O-H bonds can hydrogen bond to water. An example of an O-H bond is methanol (#CH_3#-OH). Sugars contain O-H bonds and dissolve in water.

An example of an N-H bond is methyl amine (#CH_3#-#NH_2#). Both kinds of molecules will H-bond to water to separate from each other. Note that the molecule itself will not decompose.

Not all polar molecules dissolve easily. Sugar can take a long time to dissolve, but ionic compounds take less time. This is due to its dissociation (Van't Hoff) factor. The dissociation factors tells you how many ionic species a compound or molecules can give. For molecules like sugar, it is 1. It is dependent on the ionic compound. For example, it would be 2 for NaCl and 5 for #Al_2(SO_4)_3#.

Note that not all polar molecules dissolve in water. Some molecules are immiscible, meaning they cannot mix together. An examples of this is oil and water. Ethers (such as diethyl ether, #CH_3CH_2—O—CH_2CH_3#) cannot dissolve in water. What would happen if you mix diethyl ether and water? Two layers will form, with water on the bottom. This is due to water being more dense than diethyl ether.