Water to Milk and Back Again

Science Concept:

Chemical reaction involving precipitates.

Materials:

Introduction:

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