The document discusses the preparation and chemical properties of potassium permanganate (KMnO4) and potassium dichromate (K2Cr2O7), along with their uses, particularly in oxidation reactions. It also outlines the common properties of d-block elements, highlighting their physical and chemical characteristics, as well as differences among the rows. Key reactions and properties of KMnO4 and K2Cr2O7 in various mediums are provided.

1. The Malegaon High School & Jr. College
Malegaon, (Nashik), 423203
3rd Lecture on Transition and
Inner Transition Elements
Chemistry Part I, 12th Science
By
Rizwana Mohammad

2. Compounds of Mn and Cr
(KMnO4 and K2Cr2O7):
Preparation of potassium permangnate:
i. Chemical oxidation:
3MnO2 + 6KOH + KClO3 ՜
Δ
3K2MnO4 + KCl + 3H2O
In neutral or acidic medium the green potassium manganate
disproportionates to KMnO4 and MnO2.
3K2MnO4 + 4CO2 + 2H2O → 2KMnO4 + MnO2 + 4KHCO3
3MnO4
2- + 4H+ → 2MnO4
- + MnO2 + 2H2O
ii. Electrolytic oxidation:
2K2MnO4 + H2O + [O] → 2KMnO4 + 2KOH
The oxygen evolved at the anode converts manganate to
permanganate.

3. Chemical properties of KMnO4:
a. In acidic medium:
The oxidizing reactions of KMnO4 in acidic medium.
i. Oxidation od iodide to iodine:
2MnO4
- + 10I- + 16H+ → 2Mn2+ + 8H2O + I2
ii. Oxidation of Fe+2 to Fe+3
MnO4
- + 5Fe2+ + 8H+ → 5Fe3+ + Mn2+ + 4H2O
iii. Oxidation of H2S
H2S → 2H+ + S2-
5S2- + 2MnO4
- + 16H+ → 2Mn2+ + 5S + 8H2O
iv. Oxidation of oxalic acid
2MnO4
- + 5H2C2O4 + 6H+ → 2Mn2+ + 10CO2 + 8H2O
b. In neutral or weakly alkaline medium:
i. Oxidation of iodide I- to iodate IO3
- :
2MnO4
- + H2O + I- → 2MnO2 + 2OH- + IO3
-
ii. Thiosulphate (S2O3
2-) is oxidised to sulphate (SO4
-2):
8MnO4
- + 3S2O3
2- + H2O → 8MnO2 + 6SO4
-2 + 2OH-
iii. Manganous salt is oxidised to MnO2
2MnO4
- + 3Mn2+ + 2H2O → 5MnO2 + 4H+

4. Uses of KMnO4:
• As antiseptic.
• For unsaturation test in laboratory.
• In volumetric analysis of reducing agents.
• For detecting halides in qualitative analysis.
• Powerful oxidising agent in laboratory and industry.
K2Cr2O7:
Preparation of potassium dichromate:
• In the industrial production, finely powdered chromite ore
(FeOCr2O3) is heated with anhydrous sodium carbonate and a flux of
lime in air in a reverberatory furnace.
4(FeO.Cr2O3) + 8Na2CO3 + 7O2 ՜
Δ
8Na2CrO4 + 2Fe2O3 + 8CO2
• Sodium chromate formed is extracted with water and treated with
concentrated sulphuric acid to get sodium dichromate and hydrated
sodium sulphate.
2Na2CrO4 + H2SO4 → Na2Cr2O7 + Na2SO4.H2O

5. • Addition of potassium chloride to concentrated solution of sodium
dichromate precipitates less soluble orange-red coloured potassium
dichromate.
Na2Cr2O7 + 2KCl → K2Cr2O7 + 2NaCl
Chemical properties of K2Cr2O7:
i. K2Cr2O7 + 6KI + 7H2SO4 → 4K2SO4 + Cr2(SO4)3 + 7H2O + 3I2
ii. K2Cr2O7 + 4H2SO4 + 3H2S → K2SO4 + Cr2(SO4)3 + 7H2O + 3S
Common properties of d block elements:
Physical properties:
i. All d block elements are lustrous and shining.
ii. They are hard and have high density.
iii. Have high melting and boiling points.
iv. They are good electrical and thermal conductors.
v. Have high tensile strength and malleability.
vi. They can form alloys with transition and non transition elements.
vii. Many metals and their compounds are paramagnetic.
viii. Most of the metals are efficient catalyst.

6. Chemical properties:
i. All d block elements are electropositive metals.
ii. They exhibit variable valencies and form coloured salts and
complexes.
iii. They are good reducing agents.
iv. They form insoluble oxides and hydroxides.
v. Iron, cobalt, copper, molybdenum and zinc are biologically
important metals.
vi. Catalyse biological reactions.
Differences:
• Most properties exhibited by d block elements are similar, the
elements of first row differ from second and third rows in
stabilization of higher oxidation states in their compounds.
• e.g. Mo(V) and W(VI) compounds are more stable than Cr(VI) and
Mn(VIII).
• Highest oxidation state for elements of first row is +7 and in the
case of 3rd row +8 oxidation state as in RuO4 and OsO4.