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Elementary Science Education

 Solubility/insolubility of various things in water

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      Bernard Nebel
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      Sugar is notably soluble (it will dissolve) in water; fats and oils are insoluble in water (they will not dissolve). Why? Review the molecular structure of the sugar glucose shown in Lesson A 20. It has a number  of.  — O—H  groups covalently bonded to and coming off to the side of carbon atoms. These OH groups have the same kind of polarity as described for water molecules themselves. Therefore, water molecules readily hydrogen bond with the OH groups on the sugar molecules bringing them into solution. Fat and oil molecules, on the other hand, have no such groups. They will not hydrogen bond with water. They are therefore insoluble.

      What about salt? The polarity of water molecules causes them to collect around both positive and negative ions bringing them into solution, i.e., causing the salt to dissolve as seen in the following video.

      Most minerals and rocks will not dissolve, however. The Ionic bonding between their atoms is simply too strong to allow water molecules to get in between.

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