Flashcards in Chemistry 12: Solution Equilibrium Deck (10):

1

## What is a solution equilibrium?

###
an equilibrium involving saturated solutions of slightly soluble ionic compounds

-low solubility (precipitates)

-equilibrium between solid and dissociated ions

The rate of dissolving = rate of precipitation

*undissolved solute enter the solute = dissolved solute precipitates from the solution

*PHYSICAL SYSTEM (no chemical changes)

-->therefore can say dissolving

Macroscopic constant, lots going on microscopically

-number of ions in solution and number of crystals undissolved (precipitate) is constant

-temperature change will offset and shift the equilibrium (change Ksp value)

2

## What is the solubility of a substance for a given temperature?

### The concentration of the ions in solution is the solubility of the substance for a given temperature

3

## How to write a solution/solubility equilibrium equation?

###
The equation is the dissociated equation of a solid

-subscripts in solid compound became the coefficient in the ions

-include states and charges

-must balance (charges in ions)

ex: Ag2S(s) 2Ag+(ag) + S^2-(aq)

4

## How to write a Ksp expression?

###
Solubility Product Constant (Ksp): product of the ion concentrations present

-must be in concentration mol/L

-do not include solid solute (concentration is constant)

-coefficient in balanced equation become the power that the ion concentration is raised to

*No units for Ksp

**Ksp is for a solute/compound ex: the Ksp for AgBr

5

## What two equations do you always need for solution equilibrium problems/calculations?

### Solution Equilibrium Equations & Ksp expression

6

## Ksp values and the relationship to solubility

###
All compounds studied have a low solubility because they saturate quickly in pure water

-Therefore must now rank the compounds with same mole ratio

Low Ksp value = low solubility substance (low ion concentrations, meaning more precipitate and fewer ions dissolved in the solution)

High Ksp value = higher solubility substance

7

## Calculate Ksp from Ion concentrations

###
Solubility (concentration) of a solid compound (solute that dissociates) is stoichiometrically related to the ion concentrations

1) write solution equilibrium equation

2) identify mole ratio -->individual concentrations

3) write Ksp expression

4) sub in ion concentrations

**differentiate between solubility and ion concentrations by looking at the charges (ions)

8

## Calculating Ion Concentrations/Solubility from Ksp

###
1) write solution equilibrium equation

2) identify mole ratio

3) Write Ksp expression, using 'x' for individual ion concentrations

4) solve for x (concentration)

5) concluding statement with units (mol/L)

1:1 Ksp = x^2

1:2 Ksp = 4x^3

1:3 Ksp = 27x^4

9

##
Solubility Conversions

between mol/L and g/L, g/100ml, g/ml etc.

###
*Ksp must have concentrations and solubility in Mol/L

Beginning of Ksp problem:

If given solubility/ion concentration in g/L -->want mol/L

**mathematically solve by cancelling units

g/L divide by mm (xmol/g) = mol/L

End of Ksp problem:

Solubility/ion concentration is in mol/L, but required in g/L

mol/L x mm (g/mol) --> g/L

Required in g/100 ml

g/1000mL divide by 10 top and bottom--> xg/100ml

10