3. Chemical properties to molybdenum and tungsten

3.1. Place 2-3 mls of 0,5N ammonium molybdate solution into a test tube, add 3-4 drops of concentrated hydrochloric acid and 1-2 granules of metallic zinc. What occurs? Give the equations of the relevant reactions, taking into account, that the following compounds are formed: (NH₄)₂[MoOCl₅] is green, and (NH₄)₄[MoOCl₄] is brown.

3.2. Place 2-3 mls of 0,5N ammonium molybdate solution into a test tube and add by drops diluted nitric acid, avoiding its excess amount, until precipitate forms. Divide the precipitate in two parts in two test tubes and add excess amount of 1 M hydrochloric acid solution to one of them, and excess amount of 1 M sodium hydroxide solution to the second. What occurs? Give the equations of the relevant reactions and make a conclusion on acid-base properties of compound.

3.3. Place 2-3 mls of 0,5N ammonium tungstenate solution into a test tube and add by drops diluted nitric acid, avoiding its excess amount, until precipitate forms. Divide the precipitate in two parts in two test tubes and add excess amount of 1 M hydrochloric acid solution to one of them, and excess amount of 1 M sodium hydroxide solution to the second. What occurs? Give the equations of the relevant reactions and make a conclusion on acid-base properties of compound.

Laboratory work 16

ELEMENTS of MANGANESE SUBGROUP

Themes for home preparation

General characteristic of manganese subgroup elements. A structure of manganese atom, its oxidation states. Occurrence in nature, obtaining of metallic manganese, its properties. Compounds of manganese (II): oxide, hydroxide, their obtaining, acid-base properties, salts. Oxides of manganese (IV) their obtaining and properties. Manganates, obtaining and properties, interaction with water. Oxide of manganese (VII), permanganic acid and permanganates, their obtaining and properties. Dependence of oxidation-reduction properties of manganese compounds on рH of medium.

Technetium, rhenium. Structure of atoms, oxidation states, obtaining and properties. Compounds of rhenium (VII): oxides, perrhenic acid, perrhenates. Oxidation-reduction properties of rhenium compounds. Comparation of properties of manganese, technetium, rhenium and their compounds.

Questions and tasks

1. How are manganese subgroup metals received in industry? Give the equations of the relevant reactions.

2. What electronic structure do manganese subgroup elements atoms have? What oxidation states can these elements have in compounds? Give examples.

3. What is the position of manganese, technetium and rhenium in the electromotive series of metals? With what acids do they react? Give the equations of the relevant reactions.

4. How do the acid-base properties of manganese oxides and hydroxides change? How do they react with acids and alkalis?

5. Give examples of reactions, in which manganese (IV) oxide acts as an oxidising agent, reducing agent and does not change an oxidation state.

6. How and why do oxidising properties of permanganate-ion depend on acidity of solution? Give the equations of relevant reactions.

7. What volume of 0,01 N potassium permanganate solution can be reduced by 100 mls of hydrogen sulphide at the temperature of 0° and at the pressure of 101,3 kPa in the presence of excess amount of sulfuric acid?

8. Give the equations of reactions of potassium permanganate interaction with sulfurous acid and with hydrogen peroxide in acidic, neutral and alkaline medium.

9. How and why do the thermal stability, acid-base and oxidising properties in a range of acids HMnO₄ - HTcO₄ - HReO₄ change?