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An effective solvent is one that has a stronger affinity for molecules composing a solid than the molecules in the solid do for each other. For example:
NaCl, sodium chloride, is a solid at room temperature. It is an ionic solid, and the interactions between Na+ and Cl- ions in a NaCl crystal are extremely polarized. In order to disrupt the Na+ Cl- interaction in a crystal and thus dissolve the salt, a polar solvent is needed. Water has a strong dipole moment, with a positive "end" to the molecule (towards the hydrogens) and a negative "end" (towards the oxygen). Water is a good solvent for NaCl because the positive "end" of water can surround the Cl- atoms in the NaCl crystal, and the negative "end" of water can surround the Na+ atoms, effectively pulling them apart, dissolving them, or solvating them.
In general, remember the saying "like dissolves like":
- a polar solvent (like water or ethanol, for example) will dissolve an ionic solid or a solid composed of molecules with a dipole moment
- a non-polar solvent (like hexanes, benzene, or many other organic solvents) will dissolve a solid composed of all the same type of atom, or of non-polar molecules such as oils.
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Aug 31st, 2015
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