Water to Milk and Back Again

Science Concept:

Chemical reaction involving precipitates.

Materials:

• 3 g solid anhydrous calcium chloride
• 500 mL distilled water
• 10 mL ammonium oxalate (0.1 M) or 4 g. per 100 mL water.
• 45 mL 6 M nitric acid
• 3 beakers

Introduction:

How many of you like to drink water for dinner? How many of you like to drink milk? Well I like to drink both so lets see if I could turn this water into milk and then turn it back into water again.

Procedure:

1. Dissolve 3 g solid anhydrous calcium chloride in 500 mL if distilled water.

2. In a 2nd beaker place 10 mL of ammonium oxalate.

3. In a 3rd beaker place 45 mL of 6 M nitric acid.

4. Pour the calcium chloride solution into the beaker with ammonium oxalate (Milk)

5. Pour the "milk" into the 3rd beaker with nitric acid (water).

Explanation:

When the calcium chloride solution is mixed with the ammonium oxalate a white precipitate of calcium oxalate is produced (milk). When you combine this with nitric acid it turns clear again because the calcium oxalate dissolves.

CaCl₂ + (NH₄)₂(C₂ O₄ ) ----> CaC₂ O₄ + NH₄ Cl

Ca (C₂O₄) + HNO₃ ----> Ca(NO₃ )₂ + H₂(C₂O₄)

In these chemical reactions the starting chemicals switch partners. The positive and negative ionis switch partners.

Reference: Chem, P, Entertaining and Educational Demonstrations, Chemical Elements Publishing Company, 1974, p. 13