Dissolve balance


dissolution equilibrium can act on the compound application. Dissolved solids may be covalent compounds (organic compounds: sugars and inorganic compounds: hydrogen chloride) or an ionic compound (e.g., salt, i.e. sodium chloride), when the main difference between them will ionizing ionic compound is dissolved in water ion (covalently compounds may also, such as acetic acid, hydrogen chloride, nitrate, lead acetate). Water is the most commonly used solvents, but the same principles apply to any solvent. Concentration

in environmental science, all dissolved in water solid material (whether or not saturated) is referred to as total dissolved solids (TDS).

nonionic compounds

dissolved organic solids balance is a balance between its solid portion and the soluble fraction:

and balanced expression can be written as follows (this applies to any such reaction):

K is the equilibrium constant, representing the respective braces activity substance, and by definition, the solid matter the activity is 1. If the interaction between the ionic atmosphere can be ignored (a common situation is that very low concentrations of the solution), the concentration can also be used instead of the activity:

brackets represent a molar concentrations (usually expressed in M).

This expression was dissolved upon reaching said equilibrium concentration of dissolved sugars contained in the water is equal to K. At 25 ℃, when the standard concentration of 1mol / L, sucrose K = 1.971, which is capable of dissolving at 25 ℃ sucrose maximum amount, then the solution is called "saturated." If the current is below the saturation concentration of the solution concentration, the solid will continue until the two are equal or dissolve all solids have been dissolved; if the current concentration of the solution above the saturation concentration of the solution at this time is "supersaturated" will sucrose solution as a solid precipitate, until the two are equal. This process can be slow, but equilibrium constant is described equilibrium state of the system, not the speed of the system to reach equilibrium.

Dissolve balance

ionic compound

ionizing ionic compound usually occurs at the time of dissolution, i.e., dissociate into ions under the action of water. Such as calcium sulfate:

For the above example, expression is balance:

K is called the equilibrium constant, The curly braces represents the activity. Activity of the solid substance, by definition, equal to one. When the concentration of the solution is very low, i.e., ion activity can be seen as 1, this expression can be rewritten as the following "solubility product" expression:

this expression describes the aqueous solution of calcium sulfate equilibrium product concentration of both ions by the ionized calcium sulfate equal to K sp , of the instant product. Solubility product of calcium sulfate was 4.93 × 10 -5 . If the solution containing calcium sulfate only, i.e. only by containing ionized Ca and SO 4 , then the concentration of each ion is:

when the counting number one solute ionization unequal parts:

K sp is determined slightly complex. For ionization follows:


and solubility of the solubility product is determined by the following equation:

where: n is the total number of metering right ionization equations (for the above example, x + y), dimensionless; x is the total number of metering of all cations, dimensionless; Y is the total number of metering all anionic, dimensionless; K sp is the solubility product, (mol / kg); C is the solubility (mass of the mass ratio of the solution a) compound a, dimensionless; M M is compound a molar mass of, kg / mol.

The above equation is assumed that the ionization process occurs in a pure solvent (no occurrence of common ion effect), nor the presence of complexing and hydrolysis (i.e., present in the solution only B and C), and the concentration of the ion activity can be small It is considered equal to 1.

ion effect

ion effect refers to a mobile equilibrium dissolution occurred based on Le Chatelier's Principle. In the above example, is added as a sulfate ion (i.e., addition of soluble sulfates, such as sodium sulfate, etc.) to a saturated solution of calcium sulfate will cause the calcium sulfate precipitation, ion concentration until product solubility product meet up again.

Salt Effect

means that the salt effect of other salts present in the solution, even without the same ion, also affect the ionic strength, thereby affecting the ion activity. Therefore, even if K sp kept constant, the solubility is also changed (still the default activity is a solid).

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