Colorful Precipitates

Purpose:

To demonstrate the predictability of double replacement reactions, the use of solubility rules, and to provide an opportunity for students to write out formulas, total ionic and net ionic equations.

Materials:

• 12 test tubes
• Test tube rack

Reagents:

• 0.1 Potassium iodide (KI)
• 0.1M Barium chloride (BaCl₂)
• 0.1M Copper chloride (CuCl₂)
• 0.1M Lead (II) nitrate (Pb(NO₃)₂)
• 0.1M Potassium chloride (KCl)
• 0.1M Potassium dichromate (K₂Cr₂O₇)
• 0.1M Silver nitrate (AgNO₃)
• 0.1M Sodium carbonate (Na₂CO₃)
• 0.1M Sodium sulfate (Na₂SO₄)
• 0.1M Nickel (II) chloride (NiCl₂)

Hazards and PPE:

• Silver nitrate is toxic and contact with skin should be avoided.
• Barium chloride is an acute toxin. Handle with care.
• Copper chloride is a serious irritant. Handle with care.
• Lead nitrate is an oxidizer, acute toxin, reproductive toxin, and aquatic hazard. Store, handle, and dispose of with care.
• Nickel chloride is an acute toxin, environmental hazard, germ cell mutagen, carcinogen, and reproductive toxin. Handle and dispose of with care.
• Potassium dichromate is an oxidixer, acute toxin, carcinogen, and reproductive toxin. Store and handle with extreme care.
• Wear approved safety goggles and gloves.

Protocol:

Preparation

1. Label 12 test tubes as follows:
   1. 1. AgNO₃
      2. K₂Cr₂O₇
      3. NiCl₂
      4. Na₂CO₃
      5. Pb(NO₃)₂
      6. KI
      7. AgNO₃
      8. KCl
      9. BaCl₂
      10. Na₂SO₄
      11. CuCl₂
      12. Na₂CO₃
2. Fill each tube 1/3 full of its labeled solution.

Demonstration

1. Mix tubes according to the following instructions:
   1. Tube 1 into tube 2
   2. Tube 3 into tube 4
   3. Tube 5 into tube 6
   4. Tube 7 into tube 8
   5. Tube 9 into tube 10
   6. Tube 11 into tube 12

Disposal:

• Solutions should be placed in appropriately labeled waste containers, taking care to rinse all of the precipitates into the waste container.

Reactions:

• Silver nitrate and ammonium thiocyanate produce a brown precipitate, silver thiocyanate.
• Nickel chloride and sodium carbonate produce the pale blue precipitate, nickel carbonate.
• Lead nitrate and potassium iodide produce the yellow precipitate, lead iodide.
• Silver nitrate and potassium chloride produce a white milky precipitate.
• Barium chloride and sodium sulfate produce the white precipitate, barium sulfate.
• Copper (II) chloride and sodium carbonate produce the pale blue precipitate, copper (II) carbonate.

Citations:

1. Summerlin, L., Borgford, C., and Ealt, J. Chemical Demonstrations, Volume 2, 1987.