Determination of the solubility-product constant for a sparingly soluble salt

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Determination of the solubility-product constant for a sparingly soluble salt

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Determination of the solubility-product constant for a sparingly soluble salt

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Experiment 27

March 9, 2010

Dr. Scott Buzby, Ph.D.

Determination of the solubility-product constant for a sparingly soluble salt

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:

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

A – Absorbance of the solution

a – Molar absorption coefficient (constant)

b – Path length (constant)

c - Concentration

- 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, [CrO42-], 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