Expt 025 -- Using Solubility Rules

A variety of aqueous solutions is mixed together, two at a time, to determine which combinations produce a precipitate. On the basis of combining reaction patterns, a set of numbered "unknown" solutions is studied and relabeled.

Safety

Barium compounds are very toxic. Bismuth, silver, and soluble sulfide compounds are toxic. Wear goggles and apron. Do not ingest the chemicals. Sodium hydroxide is caustic and corrosive to skin. Silver solutions cause stains. Wash spills immediately with large amounts of water. Wash hands after the experiment.

Procedure

1. Use a 96-well plate or an acetate sheet. Obtain a set of plastic transfer pipets that contain the known solutions. Set up the solutions in the order of the data table for known solutions. Both dark and light color changes occur so 2 backgrounds are required. It is somewhat easier to use the 96-well plates when changing backgrounds.
2. Select the plastic transfer pipet for the first known solution listed in the data table. Add 4 drops of this solution to each well in the row assigned to that chemical in the 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 certain that the chemicals are placed in the wells that correspond with each solution on the data table.

   !!!Click here to See Picture.

3. When no visible reaction occurs, record "NVR" in the data table.
4. Discard the solutions into a disposal jar provided by the instructor. Clean the microplate or acetate sheet with running water. Precipitates that cling in wells may be cleaned by using a Q-tip (cotton swab) in the well. Clean any other glassware or equipment used. The plastic transfer pipets that contain the known solutions should be returned to the place where they were obtained.
5. Obtain a set of plastic transfer pipets that contain the unknown solutions numbered 1 through 8. Make sure the plastic transfer pipets are set up in the order of the data table for unknown solutions. Repeat the combining procedure using the unknown solutions and record the observations on the data table for unknowns.
6. Discard the solutions into a disposal jar provided by the instructor. Clean the microplate or acetate sheet with running water. The plastic transfer pipets that contain the unknown solutions should be returned to the place where they were obtained.

Questions

1. Prepare a table listing the cation and anion in solution from each of the following salts: BaCl₂, BiCl₃, AgNO₃, NaBr, NaI, NaOH, Na₂SO₄, and Na₂S.
2. Write net ionic equations to describe the formation of the solid for each combination in which a solid is observed.
3. Solutions A, B and C yield the following results:
   • A and B produce a white precipitate,
   • B and C produce a brown/black precipitate, and
   • A and C produce no visible reaction.

   Using the data table for known solutions, determine a possible identity combination for these three unknown solutions. Justify the answer.

4. Mixing two unknown solutions produces a dark yellow precipitate. Identify possible combinations.

Handout

Name ___________________________ Class ________

Teacher__________________________

SmallScale 25 Using Solubility Rules

Makeup students should use the pictures on the CD-ROM to record data and identify unknowns.

Data Table Knowns:

	Na2S	NaOH	NaBr	NaI	BiCl3	Na2SO4	AgNO3	BaCl2
Na2S
NaOH
NaBr
NaI
BiCl3
Na2SO4
AgNO3
BaCl2

Unknown number ______

Curriculum-

• Use this activity when discussing solutions, salts, solubility, net ionic equations, or descriptive chemistry. The student questions are aimed at skills involving the use of net ionic equations. If the activity is used before net ionic equations are covered, revise the questions.
• Although the logical puzzle presented in this problem has value almost any time, the chemistry is complex. Early in the course use Experiment 015, Combining Cations and Anions, instead of this experiment.

Safety-

Barium compounds aver very toxic. Bismuth, silver, and soluble sulfide compounds are toxic. Wear goggles and apron. Do not ingest the chemicals. Sodium hydroxide is caustic and corrosive to skin. Silver solutions cause stains. Wash spills immediately with large amounts of water. Wash hands after the experiment.

Time-

Teacher Preparation: 30 minutes

Class Time: 40 minutes

Materials-

• The following chemicals stored in plastic transfer pipet storage devices:(prepare 3 mL of each)
  • 0.1 M BaCl₂ (Dissolve 2.443 g barium chloride dihydrate (BaCl₂¥2H₂O) in enough water to make 100 mL solution.)
  • 0.1 M BiCl₃ (Dissolve 3.153 g bismuth trichloride (BiCl₃) in enough 0.1 M HCl to make 100 mL solution.)
  • 0.1 M HCl (Add 3.3 mL 3 M HCl to enough water to make 100 mL of solution.)
  • 0.1 M AgNO₃ (Dissolve 1.699 g silver nitrate (AgNO₃) in enough water to make 100 mL solution.)
  • 0.1 M NaBr (Dissolve 1.03 g sodium bromide (NaBr) in enough water to make 100 mL solution.)
  • 0.1 M NaI (Dissolve 1.50 g sodium iodide (NaI) in enough water to make 100 mL solution.)
  • 1.0 M NaOH (Add 33 mL of 3 M NaOH to enough water to make 100 mL of solution.)
  • 0.1 M Na₂SO₄ (Dissolve 1.420 g sodium sulfate (Na₂SO₄) in enough water to make 100 mL solution.)
  • 0.1 M Na₂S (Purchase this as a 0.1 M solution; or, dissolve 2.402 g sodium sulfide nonahydrate (Na₂S¥9H₂O) in enough water to make 100 mL solution.)
• 96-well plate or acetate sheet
• 9 storage pipets for solutions
• 2 cotton swabs or Q-tips
• 2 racks for storing the plastic transfer pipet such as an audio tape box.

Disposal-

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

Data Table-

	Na2S	NaOH	NaBr	NaI	BiCl3	Na2SO4	AgNO3	BaCl2
NaOH		NVR	NVR	wf	NVR	br	NVR	w cld
NaBr			NVR	NVR	NVR	y cl	NVR	NVR
NaI				NVR	NVR	g cl	NVR	NVR
BiCl3					w	w cl	bl	NVR
Na2SO4						w	NVR	w cl
AgNO3							bl	w cr
Na2S								w cld
BaCl2

NVR = no visible reaction; wf = white flocculent; br = brown; w cld = white cloudy; y cl = yellow clumps; g cl = gold clumps; bl = black; w = white; w cl = white clumps; w cr = white crystals

Note: bismuth salts hydrolyze in water producing insoluble white precipitates. Sodium sulfide hydrolyzes producing OH^-, and these solutions can react forming insoluble hydroxides.

Answers-

Q1. Prepare a table listing the cation and anion in solution from each of the following salts: BaCl₂, BiCl₃, AgNO₃, NaBr, NaI, NaOH, Na₂SO₄, and Na₂S.

A1.

Salt	Cation	Anion
BaCl2	Ba2+	Cl-
BiCl3	Bi2+	Cl-
AgNO3	Ag+	NO3-
NaBr	Na+	Br-
NaI	Na+	I-
NaOH	Na+	OH-
Na2SO4	Na+	SO42-
Na2S	Na+	S2-

Q2. Write net ionic equations to describe the formation of the solid for each combination in which a solid is observed.

A2. Net ionic equations for solid formation are:

Ag⁺(aq) + Cl^-(aq) --> AgCl(s)

Ba²⁺(aq) + 2 OH^-(aq) --> Ba(OH)₂(s)

Ba²⁺(aq) + SO₄^2-(aq) --> BaSO₄(s)

Bi²⁺(aq) + 3 OH^-(aq) --> Bi(OH)₃(s)

2 Bi²⁺(aq) + 3 S^2-(aq) --> Bi₂S₃(s)

Ag⁺(aq) + Br^-(aq) --> AgBr(s)

Ag⁺(aq) + I^-(aq) --> AgI(s)

2Ag⁺(aq) + 2OH^-(aq) --> Ag₂O(s) + H₂O

2 Ag⁺(aq) + S^2-(aq) --> Ag₂S(s)

Q3. Solutions A, B and C yield the following results:

A and B produce a white precipitate,

B and C produce a brown/black precipitate, and

A and C produce no visible reaction.

Using the data table for known solutions, determine a possible identity combination for these three unknown solutions. Justify the answer.

A3. Four possible combinations:

A = NaCl B = AgNO₃ C = NaOH

A = NaCl B = AgNO₃ C = Na₂S

A = NaOH B = BiCl₃ C = Na₂S

A = BaCl₂ B = Na₂S C = BiCl₃

Q4. Mixing two unknown solutions produces a dark yellow precipitate. Identify possible combinations.

A4. NaI and AgNO₃

Makeup Ans.-

Not operational in web version.

Reference-

An early version of this experiment was developed by Barbara Maloney, Crete, IL and Elaine M. Jetty, Ravena, NY at the 1987 Dreyfus Woodrow Wilson summer program.

Key Words 1-

solutions, salts, solubility, net ionic equations, descriptive chemistry

Elements-

Ag Ba Bi Br Cl I S O