11.2 Metal vs. Nonmetal Oxides

Chemical Concepts Demonstrated: Basicity of metal oxides, acidity of nonmetal oxides

Demonstration:

  1. BaO is dissolved in water containing phenolphthalein.
  2. The flask contains distilled water with bromothymol blue indicator already made blue by 0.1M NH3. The test tube contains chunks of dry ice. The flask and the test tube are connected with glass tubing as shown in the picture.
  3. Red phosphorus is ignited and immersed in a flask of O2 gas. The P4O10 produced is dissolved in water that contains bromothylmol blue indicator already made blue by 0.1M NH3.

Observations:
1. The solution turns from colorless to pink.
2. As the CO2 is given off, the indicator changes from blue to green and then to yellow,
3. The solution turns from blue to green to yellow.

Explanations (including important chemical equations):

    Metal oxides that dissolve in water react with water to form basic solutions.

    BaO (s) + H2O(l) ---> Ba 2+(aq) + 2 OH - (aq)

    Nonmetal oxides react with water to from acidic solutions.

    CO2 (g) + H2O(l) ---> H2CO3 (aq)

    P4O10 (s) + 6 H2O(l) ---> 4 H3PO4 (aq)