Using Solubility Rules

Introduction

During a chemical reaction, the formation of insoluble products or precipitates depends upon the solubility of that product in water (or other solvent used). The formation of a precipitate from a combination of known ions can be predicted by examining the solubility products, or Ksp values, and/or tables which list the solubilities of various known compounds. These predictions can be tested experimentally by preparing different combinations of various known ions and observing the products formed by their interactions.

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1. Obtain a microplate or a plastic sheet and a set of Beral pipets that contain the known solutions. Make sure the Beral pipets are set up in the order of your data table for known solutions. Select the Beral pipet for the first known solution listed on your data table. Add 4 drops of this solution to each well in the row assigned to that chemical on your data table. (Make puddles of 2 drops on acetate sheets if these are used instead of 96-well plates.) Repeat this for the other seven known solutions, making sure that the chemicals are placed in the wells that correspond with each solution on your data table. Where no visible reaction occurs you may want to record "NVR" on the data table.
2. Clean the microplate or acetate sheet with running water. "Stubborn" precipitates may be cleaned by using a Q-tip or cotton swab in the well. Clean any other glassware or equipment used. The Beral pipets that contain the known solutions should be returned to the place where they were obtained.
3. Obtain a set of Beral pipets that contain the unknown solutions numbered 1 through 8. Make sure the Beral pipets are set up in the order of your data table for unknown solutions. Repeat the combining procedure using the unknown solutions and record your observations on your data table for unknowns.
4. Clean the microplate and other glassware/equipment. The Beral pipets that contain the unknown solutions should be returned to the place where they were obtained.

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1. Prepare a list of the chemicals provided. Write a set of ionic equations showing the ionization of each solid ionic compound in water.

   For example:

   BaCl₂(s) --> Ba²⁺(aq) + 2 Cl^-(aq)

2. Using solubility and/or Ksp tables, predict the possible precipitation products of the various combinations of ions present in the solutions. Set up a data table for predicting the possible precipitates formed from the various combinations of ionic compounds.
3. Set up a data table for recording your observations of the precipitates formed from the various combinations of known ionic compounds. Since you are reacting each ion with every other ion, a grid with a list of all the known reagents listed both vertically and horizontally may be the easiest way to present the data. (You may also use the data sheets that come with this write-up.)
4. Write net ionic equations for the reactions that produce insoluble products.
5. Set up a data table for recording your observations of the precipitates formed from the various combinations of unknown ionic compounds. (Note: The unknown solutions will be labeled 1 through 8.)

Questions:

1. Identify each of the unknowns by number, name and formula.
2. If mixing two of your unknown solutions produces a brown precipitate, which solution combinations would be possible?
3. If mixing two of your unknown solutions produces a yellow precipitate, which solution combination would be possible?
4. You are given solutions A, B and C and the following results:

   A and B produce a white precipitate,

   B and C produce a brown precipitate, and

   A and C produce no visible reaction.

5. Using your data table for known solutions, determine a possible identity combination for these three unknown solutions. Explain your answer.

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Safety

Collect waste BaCl₂, BiCl₃, and AgNO₃ in a "heavy metal container", and dispose of as required by local laws.

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1. BaCl₂(s) --> Ba²⁺(aq) + 2 Cl^-(aq)

   BiCl₃(s) --> Bi³⁺(aq) + 3 Cl^-(aq)

   AgNO₃(s) --> Ag⁺(aq) + NO₃^-(aq)

   NaBr(s) --> Na⁺(aq) + Br^-(aq)

   NaI(s) --> Na⁺(aq) + I^-(aq)

   NaOH(s) --> Na⁺(aq) + OH^-(aq)

   Na₂SO₄(s) --> 2 Na⁺(aq) + SO₄^2-(aq)

   Na₂S(s) --> 2 Na⁺(aq) + S^2-(aq)

2. Suggested data tables are available for student use.
3. Suggested data tables are available for student use.
4. Ag⁺(aq) + Cl^-(aq) --> AgCl(s)

   Ba²⁺(aq) + 2 OH-(aq) --> Ba(OH)₂(s)

   Ba²⁺(aq) + SO₄^2-(aq) --> BaSO₄(s)

   Ba²⁺(aq) + S^2-(aq) --> BaS(s)

   Bi³⁺(aq) + 3 OH^-(aq) --> Bi(OH)₃(s)

   2 Bi³⁺(aq) + 3 SO₄^2-(aq) --> Bi₂(SO₄)₃(s)

   2 Bi³⁺(aq) + 3 S^2-(aq) --> Bi₂S₃(s)

   Ag⁺(aq) + Br^-(aq) --> AgBr(s)

   Ag⁺(aq) + I^-(aq) --> AgI(s)

   Ag⁺(aq) + OH^-(aq) --> AgOH(s)

   2 Ag⁺(aq) + S^2-(aq) --> Ag₂S(s)

5. Results for known solutions are included for teacher. Teachers are responsible for identification of unknowns. Also, suggested data tables are available for student use.

   

6. Same as #5.

Answers to Questions:

1. Identification of unknowns up to individual teacher.
2. NaOH and AgNO₃

   BiCl₃ and Na₂S

   AgNO₃ and Na₂S

3. NaI and AgNO₃
4. Four possible combinations:

   A = NaBr B = AgNO₃ C = NaOH

   A = NaBr B = AgNO₃ C = Na₂S

   A = NaOH B = BiCl₃ C = Na₂S

   A = BaCl₂ B = Na₂S C = BiCl₃

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Collect waste BaCl₂, BiCl₃, and AgNO₃ in a "heavy metal container", and dispose of as required by local laws.

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• The following chemicals stored in Beral storage devices:
  • 0.1 M BaCl₂•2H₂O (2.42 g BaCl₃•2H₂O / 100 mL solution)
  • 0.1 M BiCl₃•H₂O (3.33 g BiCl₃•H₂O / 100 mL solution using 0.1 M HCl as solvent)
  • 0.1 M AgNO₃(1.70 g AgNO₃ / 100 mL solution)
  • 0.1 M NaBr (1.03 g NaBr / 100 mL solution)
  • 0.1 M NaI (1.50 g NaI / 100 mL solution)
  • 1.0 M NaOH ( 4.0 g NaOH / 100 mL solution)
  • 0.1 M Na₂SO₄ (1.42 g Na₂SO₄ / 100 mL solution)
  • 0.1 M Na₂S•9H₂O (2.40 g Na₂S•9H₂O / 100 mL solution)
• 96-well plate or acetate sheet
• Two cotton swabs or Q-tips
• Rack for holding the Beral pipets

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The Woodrow Wilson microscale version of this lesson was
developed by:

Barbara Maloney
Crete-Monee High School
West Exchange Street, Crete, IL 60417

Elaine M. Jetty
Ravena Coeymans Selkirk Senior High School
Route 9W
Ravena, NY 12143

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