Question

How do aqueous solutions of ionic and molecular compounds differ?

Answer 1

Best Answer: Ionic solutions completely dissociate into ions. i.e. NaCl becomes Na+ and Cl-.
Molecular compound donot dissociate, they remain whole compounds. i.e. CH2O remains CH2O.

? · 6 years ago

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The main differences are the ionic solutions are electrically conducting while the molecular are non-conducting. Suppose, if you compare solutions with the same molality of an ionic and a molecular substance, the effect on solvent's boiling point (increase), freezing point (decrease), and osmotic pressure (increase) will be more pronounced for the ionic solution than for the molecular. This happens because these so called "colligative properties" depend on the number of particles dissolved, and even a simple ionic substance formed with just 2 ions will have twice as much dissolved particles than a molecular solution.

Details:
The two most common of these solutions would be table salt and table sugar (sucrose) and water as the solvent. Table salt is an ionic solid compound made with Na+ and Cl- ions, positioned mostly on the vertices of cubes. When the solid is dissolved in water the ions separate from each other. A simple way to look at this is to say that because of the high dielectric constant of water (~80 Debyes), the forces between the ions decrease considerably and therefore the dissolution, separation of the ions. Both Na+ and Cl- end up surrounded by H2O species (typically about 6 - 8).
Sucrose is a molecular solid, C12H22O11, and has 8 OH groups connected to its rings. It does not split into ions, the solid crystals contain well "arranged", neutral, sucrose molecules. But the water molecules compete favorably for all these OH groups because of their large number and the constant "bombardement" of the static crystal. It end up "spliting" the crystal and sucrose end up surrounded by a large amount of H2O species interacting strongly with the OH groups of sucrose by Hydrogen bonding. This final system is much more stable than the crystal, not only for enthalpic effects (heat generated by the H-bonding formation) but also the entropy is higher, therefore a stable solution.