Aqueous SolutionsAqueous Solutions  Compounds dissolved into water.  Can contain molecules or ions in a solution.  How do you distinguish between ion or molecule?

DISSOCIATION !!DISSOCIATION !!  The ability of a compound to breakdown in a solution into individual ions  Ionic Compounds  Break down into cations and anions  Electrical conductors—ions flow through solution  Molecular Compound  Compound remains intact as “molecules,” no breakdown  Generally NOT electrical conductors

Solubility  How much solute dissolves in a solution to produce a saturated solution  Temperature and Pressure dependent  Increase with increasing temperature  Increases with decreasing temperature (ex. Water in lake)  Pressure increases, solubility increases (ex. Soda can)

Which compounds are soluble in water? 1) BaCl 2 2) Pb (NO 3 ) 2 3) Na 2 S 4) BaCO 3 5) PbS

Precipitation PredictionPrecipitation Prediction 1)Write the reactants in ionic from  breakdown into ionic form if compounds are soluble  leave as molecules if insoluble 2)Determine the solubility of the products.  Use solubility Rules

Precipitation Predictions (cont.) 3) Check to see if one product is insoluble in water.  Product will fall out of solution, identified as precipitate 4) Write the net ionic equation  Displays which ions are directly involved in the reaction, produce the precipitate  Ions existing on BOTH sides of the equation are “ spectator ions ” (do NOT participate in precipitate formation)  Spectator ions are eliminated

Example 1:Example 1:  MgSO 4 + KOH  Write the net ionic equation. Will a precipitate form?

Chemical Equilibrium so far-----  Gases  Acids and Bases  Slightly soluble Salts  Many ionic compounds—only a small fraction dissolves

Solubility EquilibriumSolubility Equilibrium  Type of equilibrium between ionic solid and a saturated solution  Equilibrium exists between ions and solid  Saturated vs. concentrated solutions are NOT the same thing  Saturation---at equilibrium

Example 1:Example 1:  BaSO 4(s)  Ba +2 (aq) + SO 4 -2 (aq)  Indicates salt exists in “solubility equilibrium”—some dissolves, some does not

Solubility vs. Solubility Constant  Solubility—  How much compound can be dissolved  Molarity of a saturated solution  How much ionic solid can dissolve in a liter of solution  Solubility Product/constant  Numerical value of equilibrium constant  Specific for an equation representing ionic substance dissolving in water

Solubility Product Constant (Ksp)  Equilibrium constant for slightly soluble salts  Indicates equilibrium between solid salt and the ions found in a solution when it dissociates  Expression represents the product of the concentrations of ions in equilibrium  Temperature dependent  Values found in table along with solubility equation (p. 678, Appendix C—p.A18)

Example 2:Example 2:  Write a Ksp expression for an equilibrium in a saturated aqueous solution of iron (III) phosphate and for an equilibrium in a separate aqueous solution of chromium (III) hydroxide.

Ksp and Solution MolarityKsp and Solution Molarity  Ksp is an equilibrium constant, NOT concentration  Molarity/concentration separate from Ksp  Ksp values  Considered estimates due to ion attractions to other ions in solution and Ksp values not exact  Used only for slightly soluble salts  Increase concentration of ions, increase Ksp value

2 Classic Ksp Problems2 Classic Ksp Problems 1)Finding solubility of a chemical substance if given its solubility product (Ksp). 2)Given the molar solubility of a chemical substance, find the solubility product (Ksp).

Example 3:Example 3:  Determine the molar solubility of CaF 2 given that Ksp= 3.9x10 -11

Example 4:Example 4:  Based on a Ksp value of 1.4 x at 25°C for silver sulfate, calculate this compound’s molar solubility at 25°C.  Ag 2 SO 4(s)  2Ag + (aq) + SO 4 -2 (aq)

Example 5:Example 5:  Given that the molarity solubility of MgF 2 = 2.1x10 -3 M, calculate Ksp for MgF 2.

Example 6:Example 6:  Without any calculations, arrange the following in order of INCREASING molar solubility.  MgF 2, CaF 2, PbCl 2, PbI 2