Procedure: (a) Mix in culture tube by shaking 0.5 g pyrolusite + 1 g NaOH + 1 g KN03. Project in H-3 and heat until molten. Cool. Shake with 30 ml water, filter equal amounts into the two cells of C-2. Project. (b) Gently add a dropperful of dil. HNOa to the liquid in cell 2. (c) Drop a small lump of dry ice into cell t.

Observations: (a) KNOa oxidizes MnO, to green man- ganate, K2MnOl. (b) HN03 oxidizes the upper por- tion of the liquid in cell 1 to purple permanganate, MnOn-. (c) Dry ice converts green MnOr into purple permanganate, Mn0,- (this is an industrial method).

Reactions: 3KZMnO4 + 2COz - 2KMn04 + 2KzCOa + MnOz.

Reference: HARPIN, R. E., J. CHEM. EDUC., 36,. A685, 1959.

Dem. 645-Oxygen from KMn04

To show: The preparation of oxygen from heating permanganate.

Materials: H-1, KMnOl, splint.

Procedure: Project H-1 with the test tube quarter- full of KMnOa. Heat with the small alcohol burner. Collect the evolved gas and test it for oxygen with a glowing splint.

Observativns: Oxygen gas is evolved, the splint bursts into flame.

4KMn0~ - 2K10 + 4MnOn + 301

Dem. 646-MnOz as a Catalyst lor H,O, Decomposilion

To shm: Catalytic action of MnOz on hydrogen per- oxide.

Materials: C-3, two splints, 3% H202, detergent, MnOz.

Procedure: Project C-3 half-filled with HzOz. (a) Wet two sticks, dip into MnOZ to collect some particles, drop the sticks into cells 2 and 3. (b) Drop some granules of detergent into cell 3.

Observations: (a) Vigorous decomposition of the HzOz occurs on the surface of the MnOz particles. (b) As the O2 gas evolves, i t rises with the detergent as a foam.

Dem. 647-Permongonote + Fe(llJ

To show: Titration of ferrous salt with standard per- manganate solution.

Materials: 0.5 N FeSOa, (NH&S04.6HzO [98.04 g per 1000 ml solution], dil HzS04, C-1, stirrer, 0.1 N KMn04 (3.16 g KMnO6 per 1000 ml solution).

Procedure: Project C-1 half-full of water. Add a dropperful of dil. H2S04. Drop in (class counting) 20 drops of 0.1 N KMnO4. Now drop in (class counting) the FeS0, solution until the pink color vanishes.

Reactions: lOFeSO4 + 2KMn04 + 8HzS04 - KzSOl + 2MnS04 + 8HzO + 5Fez(SO&

Note: Mohr's salt, (NH4)2FeSO~,6H20 can be used in place of FeS04.

Dem. 648-Pernmganate + SOz or HzS

To show: The reduction of Mn04- by SOz or HzS.

Materials: '2-3, KMnO,, NaHS03-aq, NaS-aq, HzSOr dil.

Procedure: Project C-3 with cells quarter-full of dilute H2S04. Add varying amounts of dil. KMn04 to each cell. Now titrate with NaHSOa-aq or NaS-aq.

Observations: The violet KMn04 is reduced to color- less (pink) Mn+=, according to reaction as

5S01 + 2KMnO. + 2&0 - KBO, + 2MnSO. + 2H9S04

Dem. 649-Pernungunate + M02

To show: Titration of hydrogen peroxide with stan- dard permanganate solution.

Materials: 0.1 N KMnOl, dil. HzSOI, 3% HzOZ, C-1, stirrer.

Procedure: Project C-1 half-full of water. To it add a dropperful of dil. H2S04 + exactly 10 drops of KMnOl. Now add HzOa dropwise until the pink color disappears.

Reaction: 5H202 + 2KMnOa + 3H,S04 - 2 ~ k 3 0 , + KzS04 + Hz0 + 502 t . Calculations: 0.1 N KMnO, contains 3.16 g KMn04 per 1000 ml solution. From the volume of solution of Hz02 used, calculate the % HH,02 in the original solu- tion.

E. Group VIII. (Fe, Go, Ni) Dem. 650--Oxidation and Reduction of Iron

Experiment developed by Edwin H. Cooper.

To show: The oxidation of Fe(I1) and reduction of Fe(II1).

-Materials: Soln A: 0.4 g Mohr's salt (Fe(NH,),SOn,- 6Hz0) + 4 m16 M HzSOI + 100 ml water. KMnOp-aq, K2Crz0i-aq, KSCN-aq, iron picture-wire; H-3.

Procedure: Project culture tubes one-quarter full of Soln A + 1 ml KCNS;aq (mixture should be prac- tically colorless.) (a) Now add dropwise 60 red color KZCrzO7-aq to tube I , KMnOa-aq to tube 8, and HzOz to tube 3. (b) Put 1-in. lengths of iron picture-wire into each tube and boil 1 min.

Observations: (a) I<Mn04, I(2Crz0, and HzOz all oxi- dize Fe++ to Fe+++, which then forms deep red FeCNS++. (b) The iron wire reduces the ferric to ferrous; the red FeCNS++ disappears and the solu- tions turn colorless.

Reactions: (a) 2KMnOa + 10FeSOa + 8H,S01 - KzS04 + 2MnS04 + 8Hz0 + 5Fez(S04)3

(b ) K2Cr207 + 6FeSOI + 7H,S04 - CrdSOJa + 7Hz0 + 3Fe~(S04)3 + KzS04

(c) Fe+3 + CNS- + FeCNS++ deep red

A496 / Journol of Chemicol Education