Simple Dissolution
Dissolution of an organic solid can be described as an equilibrium between the substance in its solid and dissolved forms. For example, when sucrose (table sugar) forms a saturated solution
- .
An equilibrium expression for this reaction can be written, as for any chemical reaction (products over reactants):
where K is called the thermodynamic solubility constant. The braces indicate activity. The activity of a pure solid is, by definition, unity. Therefore
The activity of a substance, A, in solution can be expressed as the product of the concentration, and an activity coefficient, γ. When K is divided by γ the solubility constant, Ks,
is obtained. This is equivalent to defining the standard state as the saturated solution so that the activity coefficient is equal to one. The solubility constant is a true constant only if the activity coefficient is not affected by the presence of any other solutes that may be present. The unit of the solubility constant is the same as the unit of the concentration of the solute. For sucrose K = 1.971 mol dm−3 at 25 °C. This shows that the solubility of sucrose at 25 °C is nearly 2 mol dm−3 (540 g/l). Sucrose is unusual in that it does not easily form a supersaturated solution at higher concentrations, as do most other carbohydrates.
Read more about this topic: Solubility Equilibrium
Famous quotes containing the words simple and/or dissolution:
“I ... observed the great beauty of American government to be, that the simple machines of representation, carried through all its parts, gives facility for a being moulded at will to fit with the knowledge of the age; that thus, although it should be imperfect in any or all of its parts, it bears within it a perfect principle the principle of improvement.
”
—Frances Wright (17951852)
“We are threatened with suffering from three directions: from our own body, which is doomed to decay and dissolution and which cannot even do without pain and anxiety as warning signals; from the external world, which may rage against us with overwhelming and merciless forces of destruction; and finally from our relations to other men. The suffering which comes from this last source is perhaps more painful than any other.”
—Sigmund Freud (18561939)