Solubility Products

Solubility Products is a tool for accurate estimation of concentrations of solutes upon dissolution of solid compounds of low solubility. The tool is applicable to various chemical equilibrium tasks, such as: salt dissociation, common-ion effect, separation by sedimentation and precipitation titration.  
App includes database of low solubility compounds. The app will suggest list of compound names and chemical formulas based on the characters typed in 'Solid' field. Upon selection of the compound from database, app will provide balanced dissolution reaction and equilibrium constant.
Application derives final, equilibrium concentrations of solutes based on equilibrium constant (Ksp), initial concentrations, solubility and stoichiometric coefficients. Additionally, app calculates reaction quotient for any given concentrations and stoichiometry.

For a general dissociation chemical reaction:

S(s) = aA + bB +cC,

the Reaction Quotient (Q) is defined by:

Q = A^a * B^b * C^c

where A, B, C – are solutes (electrolytes, ions, etc.) concentrations and a, b, c are stoichiometric coefficient. Sum of powers determines the reaction order.

If Q is not equal to reaction equilibrium constant Ksp, then reaction is not at equilibrium and it will proceed (due to difference in forward and reverse reaction speeds) to the direction defined by Q.
If Q is less than Ksp reaction will move towards products (A&B&C), if Q is larger than Ksp – reverse reaction will prevail.

Example:
For given reaction: S(s) = 2A + 1B +3C, initial reaction concentrations are Ao=0.1M, Bo=0.2M, Co=0.3M and Ksp=1e-6 M6.

the Reaction Quotient (Q) is defined by:

Q = A^2 * B * C^3

Upon loading the data to “Solubility Products” app, Reaction Quotient is immediately available: Q= 5.4e-5 M6. Apparently Q>K, suggesting that reaction is too close to the products side and reverse reaction (precipitation) will prevail to bring the reaction back to the equilibrium.

The new equilibrium concentrations of reaction components can be derived from the equation:


Q = (Ao-2x)^2 * (Bo-x) * (Co-3x)^3

Apparently, solving this equation is rather demanding task, that turns to be unnecessary, since “Solubility Products” app immediately returns the answer: Aeq=28.98mM, Beq=0.1645M, Ceq=0.1935M and additionally 0.036 mole of solid precipitated.


The application features:

To start calculation user is required to fill in stoichiometric coefficients, initial concentrations of available components, solution volume and equilibrium constant Ksp or Solubility.

The solubility in pure solvent (water) only is evaluated and must be filled in and not in the current conditions. Presence of common ions can decrease solubility of solid!

Either Ksp or Solubility values must be present! When only solubility value is available the app will automatically calculate Ksp and vice versa.

Volume of solution is a must to evaluate change in amount of solid compound, it is adjustable and automatically set to 1 litre.

Important!!! If available amount of solid is not enough, then it will be completely dissolved without achieving equilibrium conditions!

When Molar mass (Mw) of solid is filled in, then solid mass and solubility calculated and inserted in g/l units, otherwise it is set to mole/l. Beware of transformations accompanied with filling and deleting of Mw value! Once Mw value is filled in and “Done” is pressed (!), a solid mass and solubility are recalculated to new units.

To start calculation initially or after updating the concentration or coefficient fields, user is requested to tap Run button! The values are valid only if Run button is greyed out!

Significant attention should be paid to concentration, solubility and equilibrium constant units!
 
The power of equilibrium constant units depicted as “x” is defined as (a+b+c), where a, b and c are the stoichiometric coefficients of the reaction.