Experiment 27March 9, 2010Dr. Scott Buzby, Ph.D.

Learn to experimentally determine the solubility constant (Ksp) for a salt

Practice operation of a spectrophotometer

Further explore the use of a calibration graph and Beer-Lambert Law

For a true equilibrium to exist between a solid and a solution, the solution must be saturated (i.e. solid material must remain at the bottom of the solution)

The solubility of silver carbonate is expressed by the equation:

][][

][

][][

2

23

22

32

23

22

2)(3

2)()(32

COAgK

COAg

COAgK

COAgCOAg

sp

c

aqaqs

We will use a spectrophotometer to determine the intensity of the color of a solution

Described on pages 310 & 312 in you text

Absorbance is related to concentration by the Beer-Lambert Law

cA

abcA

A – Absorbance of the solution a – Molar absorption coefficient

(constant) b – Path length (constant) c - Concentration

abcA

Prepare a series of solutions of a known concentration

Plot absorbance vs. concentration for the known solutions

By measuring absorbance of an unknown sample you can determine concentration using your plot (follow red arrows on graph)

Procedure on page 311

FOLLOW ALL INSTRUCTIONS PRECISELY!!!

Prepare three separate solutions according to the procedure on page 312

Determine the chromate concentration, [CrO4

2-], using your calibration graph Calculate silver concentration, [Ag+], and

Ksp for you solution (see notes on page 313)

Next Week – Nothing Enjoy Spring Break!

Next Class (3/23/2010) Report Sheet – Pgs. 315-316 Questions – Pgs. 316-317 Calibration Graph – Pg. 318 or print-out Pre-Lab Experiment 28 – Pg. 323