Principles of Solubility

Solubility and intermolecular forces. Oil (left) is made up of nonpolar molecules. It does not mix well with water because water is polar. Ethylene glycol (right), commonly used as antifreeze, mixes with water in all proportions because both form hydrogen bonds. 

The extent to which a solute dissolves in a particular solvent depends on several factors. The most important of these are 

In this section we consider in turn the effect of each of these factors on solubility. 

Most nonpolar substances have very small water solubilities. Petroleum, a mixture of hydrocarbons, spreads out in a thin film on the surface of a body of water rather than dissolving. The mole fraction of pentane, C5H12, in a saturated water solution is only 0.0001. These low solubilities are readily understood in terms of the structure of liquid water, which you will recall (Chapter 9) is strongly hydrogen-bonded. Dissimilar intermolecular forces between C5H12 (dispersion) and H2O (H bonds) lead to low solubility. 

Of the relatively few organic compounds that dissolve readily in water, many contain — OH groups. Three familiar examples are methyl alcohol, ethyl alcohol, and ethylene glycol, all of which are infinitely soluble in water. 

In these compounds, as in water, the principal intermolecular forces are hydrogen bonds. When a substance like methyl alcohol dissolves in water, it forms hydrogen bonds with H20 molecules. These hydrogen bonds, joining a CH3OH molecule to an H20 molecule, are about as strong as those in the pure substances. 

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The general principle of solubility is that like dissolves like. Hence polar polymers dissolve most readily in polar solvents, aromatic polymers in aromatic solvents, and so on. This is reflected in the thermodynamics of dissolution. 

The principle of solubility product is the major factor in governing the gravimetric analysis. Justify the statement adequately with appropriate examples. 

The industrial process by which large quantities of sodium hydroxide are made consists in treating a 10 per cent solution of sodium carbonate with an excess of calcium hydroxide (milk of lime). After the reaction is complete the mixture is filtered to remove the precipitated calcium carbonate and excess of calcium hydroxide. This process involves a most important application of the principle of solubility product calcium hydroxide continues to dissolve and calcium carbonate to precipitate according to the reaction... 

An understanding of crystallization processes begins with a knowledge of fundamental solubility relationships. The important principles of solubility and supersolubility are briefly discussed in the following paragraphs. Several complete treatises have been written on these subjects and cover the theory and data in depth (C2, R3). 

To learn more about solutions in the body, visit the Chemistry Web site at chemistrymc.com Activity Research the solutions that can be found in the human body and in animals. How do biological systems makes use of the principles of solubility to support life ... 

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