2. Oxidizing properties of nitric acid

Heat carefully a test tube with 2-3 ml of concentrated nitric acid and add a smouldered piece of coal. Observe evaluation of a brown gas of NO₂. Write down and balance the reaction.

3. Redox duality of nitrites

a) Take 1 ml of sodium nitrite in a test tube, add 1 ml of potassium iodide and 1 ml of 2 N sulfuric acid. Observe evaluation of iodine.

b) Take 1 ml of sodium nitrite into a test tube, add 1 ml of 2 N sulfuric acid and 5 drops of potassium permanganate.

Write down and balance the reactions (a) and (b).

4. Reducing properties of sulfides

Take 1 ml of an aqueous solution of iodine and add some drops of potassium sulfide solution. Write down and balance the reaction.

5. Formation of sulfides

Take 5 test tubes filled with Zn, Mn(II), Cd, Sn(II) and Pb(II) salts respectively and add potassium sulfide into each test tube. Observe colors of the formed sulfides.

6. Reducing properties of sulfites

Take 1 ml of potassium dichromate into a test tube, add sulfuric acid and sodium sulfite solution. Write down and balance the reaction.

7. Oxidizing properties of sulfuric acid

Take 2 ml of concentrated sulfuric acid in the test tube (be careful!) and add some pieces of copper. Heat the test tube if necessary. Observe the evaluation of sulfur dioxide. Write down and balance the reaction.

QUESTIONS AND PROBLEMS

1. Describe the electronic structure of ammonia and NH₄⁺ ion.

2. Using the molecular orbital method draw molecular diagrams of N₂ and O₂ molecules. Compare stabilities of these molecules.

3. Calculate pH of 0.01 M solution of NH₄OH.

4. Calculate the solubility of Ag₂SO₄: (a) in pure water; (b) in presence of 0.1 M solution of sulfuric acid.

5. Compare solubilities of MnS and CuS in diluted hydrochloric acid.

44