Review of Solubility and Precipitation

Reactions

Aqueous Solutions

Compounds dissolved into water.

Can contain molecules or ions in a solution.

How do you distinguish between ion or molecule?

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) BaCl22) Pb (NO3)2

3) Na2S

4) BaCO3

5) PbS

Precipitation 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:

MgSO4 + KOH

Write the net ionic equation. Will a precipitate form?

Solubility Product Constant (Ksp)

Chemical Equilibrium so far-----

Gases

Acids and Bases

Slightly soluble Salts Many ionic compounds—only a small fraction

dissolves

Example 1:

BaSO4(s) Ba+2(aq) + SO4

-2(aq)

Indicates salt exists in “solubility equilibrium”—some dissolves, some does not

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:

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 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

Example 3:

A saturated aqueous solution of silver carbonate contains 32 mg of Ag2CO3 per liter at 20°C. Calculate the Ksp for Ag2CO3 at 20°C.

Example 4:

Based on a Ksp value of 1.4 x 10-5 at 25°C for silver sulfate, calculate this compound’s molar solubility at 25°C. Ag2SO4(s) 2Ag+

(aq) + SO4-2

(aq)

Example 5:

Without any calculations, arrange the following in order of INCREASING molar solubility. MgF2, CaF2, PbCl2, PbI2

Homework

Ksp Practice Problem Set #1