Potassium Dichromate and Potassium Permanganate

Frequently Asked Questions (FAQs)

Join ALLEN!

(Session 2026 - 27)

Name

Mobile Number

Class

Choose class

Goal

Choose your goal

Preferred Programs

Preferred Mode

State

Choose State

I agree to

I authorise ALLEN Career Institute Pvt Ltd to send me regular updates via Phone calls, Whatsapp, SMS, Robocalls (Automated Calls), Emails, or on postal address.

Potassium Dichromate and Potassium Permanganate

1.0Potassium Dichromate K₂Cr₂O₇ and Potassium Permanganate KMnO₄

Potassium dichromate and potassium permanganate are among the most important oxidising agents used in chemistry, particularly in volumetric analysis and organic synthesis. Their unique properties and preparation methods are crucial topics for JEE, as they are part of the d- and f-block elements chapter. This guide covers their industrial preparation and key chemical properties in detail.

2.0Potassium Dichromate K₂Cr₂O₇

Potassium dichromate is a powerful oxidizing agent that appears as an orange crystalline solid.

Preparation from Chromite Ore $(F e C r_{2} O_{4})$

The preparation of K₂Cr₂O₇ involves a three-step process:

Conversion of Chromite Ore to Sodium Chromate:

Chromite ore is fused with sodium carbonate (Na_2CO_3) in the presence of air. The iron is oxidized to iron(III) oxide, and the chromium is oxidized to soluble sodium chromate.

$4 F e C r_{2} O_{4} + 8 N a_{2} C O_{3} + 7 O_{2} Δ 8 N a_{2} C r O_{4} + 2 F e_{2} O_{3} + 8 C O_{2}$
Conversion of Sodium Chromate to Sodium Dichromate:

The yellow solution of sodium chromate is acidified with sulfuric acid (H_2SO_4) Chromate ions are converted to orange dichromate ions.

$2 N a_{2} C r O_{4} + H_{2} S O_{4} \to N a_{2} C r_{2} O_{7} + N a_{2} S O_{4} + H_{2} O$
Conversion of Sodium Dichromate to Potassium Dichromate:

Potassium chloride (KCl) is added to the solution of sodium dichromate. Sodium dichromate is highly soluble, while potassium dichromate is less soluble and precipitates out.

$N a_{2} C r_{2} O_{7} + 2 K Cl \to K_{2} C r_{2} O_{7} ↓ + 2 N a Cl$

Properties

Oxidizing Nature:(K_2Cr_2O_7) acts as a strong oxidizing agent in acidic medium. The chromium(VI) is reduced to chromium(III).

$C r_{2} O_{7}^{2 -} + 14 H^{+} + 6 e^{-} \to 2 C r^{3 +} + 7 H_{2} O (E^{\circ} = + 1.33 V)$

One mole of K₂Cr₂O₇ accepts 6 electrons, so its equivalent weight is 6Molar Mass.
Action of Alkali: In an alkaline medium, the orange dichromate ion converts to the yellow chromate ion. This reaction is reversible and pH-dependent.

$C r_{2} O_{7}^{2 -} (Orange) + 2 O H^{-} ⇌ 2 C r O_{4}^{2 -} (Yellow) + H_{2} O$
Reaction with Halides: In an acidic medium, it oxidizes iodide ions to iodine and bromide ions to bromine.

$C r_{2} O_{7}^{2 -} + 14 H^{+} + 6 I^{-} \to 2 C r^{3 +} + 3 I_{2} + 7 H_{2} O$

3.0Potassium Permanganate KMnO₄

Potassium permanganate is a powerful oxidizing agent that exists as a dark purple crystalline solid.

Preparation from Pyrolusite Ore (MnO_2)

The industrial preparation of KMnO4 is also a multi-step process:

Fusion of Pyrolusite Ore to Potassium Manganate:

$2 M n O_{2} + 4 K O H + O_{2} fusion 2 K_{2} M n O_{4} (green) + 2 H_{2} O$

Finely powdered pyrolusite ore is fused with potassium hydroxide (KOH) and an oxidizing agent like potassium nitrate (KNO_3). Manganese(IV) is oxidized to green manganate(VI) ion.

Oxidative Electrolysis of Potassium Manganate:

The green solution of potassium manganate is electrolytically oxidized. Manganate(VI) ions are converted to permanganate(VII) ions at the anode.
$A t A n o d e : M n O_{4}^{2 -} \to M n O_{4}^{-} + e^{-}$
$A tC a t h o d e : 2 H_{2} O + 2 e^{-} \to H_{2} + 2 O H^{-}$
The green solution turns purple due to the formation of permanganate ions.

Properties

Oxidizing Nature: The oxidizing power of KMnO₄depends on the medium (acidic, basic, or neutral).
Acidic Medium: It is a powerful oxidizing agent. Manganese(VII) is reduced to manganese(II).

$M n O_{4}^{-} + 8 H^{+} + 5 e^{-} \to M n^{2 +} + 4 H_{2} O (E^{\circ} = + 1.51 V)$

One mole of KMnO₄ accepts 5 electrons, so its equivalent weight is 5Molar Mass.
Neutral or Faintly Alkaline Medium: Manganese(VII) is reduced to manganese(IV).

$M n O_{4}^{-} + 2 H_{2} O + 3 e^{-} \to M n O_{2} ↓ + 4 O H^{-}$

One mole of KMnO₄ accepts 3 electrons.
Strongly Alkaline Medium: Manganese(VII) is reduced to manganese(VI).

$M n O_{4}^{-} + e^{-} \to M n O_{4}^{2 -}$

One mole of KMnO₄ accepts 1 electron.
Colour: KMnO₄ solutions are intensely purple due to the charge transfer spectrum. It does not show d-d transition because Mn has a d0 configuration in the MnO_4^- ion.

4.0Key Differences Between K₂Cr₂O₇ and KMnO₄

Feature	Potassium Dichromate (K₂Cr₂O₇)	Potassium Permanganate (KMnO₄)
Colour	Orange	Dark Purple
Oxidizing Power	Strong in acidic medium only	Strong in all medium (acidic > neutral > alkaline)
Reduction Product	Cr^{3+} (Green) in acidic medium	Mn^{2+} (Colourless) in acidic medium, (MnO_2) (Brown) in neutral/alkaline medium
Equivalent Weight	Molar mass / 6 (in acidic medium)	Molar mass / 5 (in acidic medium)
Preparation	From chromite ore (FeCr_2O_4)	From pyrolusite ore (MnO_2)

Join ALLEN!

(Session 2026 - 27)

Name

Mobile Number

Class

Choose class

Goal

Choose your goal

Preferred Programs

Preferred Mode

State

Choose State

I agree to

I authorise ALLEN Career Institute Pvt Ltd to send me regular updates via Phone calls, Whatsapp, SMS, Robocalls (Automated Calls), Emails, or on postal address.

Potassium Dichromate and Potassium Permanganate

1.0Potassium Dichromate K₂Cr₂O₇ and Potassium Permanganate KMnO₄

Potassium dichromate and potassium permanganate are among the most important oxidising agents used in chemistry, particularly in volumetric analysis and organic synthesis. Their unique properties and preparation methods are crucial topics for JEE, as they are part of the d- and f-block elements chapter. This guide covers their industrial preparation and key chemical properties in detail.

2.0Potassium Dichromate K₂Cr₂O₇

Potassium dichromate is a powerful oxidizing agent that appears as an orange crystalline solid.

Preparation from Chromite Ore $(F e C r_{2} O_{4})$

The preparation of K₂Cr₂O₇ involves a three-step process:

Conversion of Chromite Ore to Sodium Chromate:

Chromite ore is fused with sodium carbonate (Na_2CO_3) in the presence of air. The iron is oxidized to iron(III) oxide, and the chromium is oxidized to soluble sodium chromate.

$4 F e C r_{2} O_{4} + 8 N a_{2} C O_{3} + 7 O_{2} Δ 8 N a_{2} C r O_{4} + 2 F e_{2} O_{3} + 8 C O_{2}$
Conversion of Sodium Chromate to Sodium Dichromate:

The yellow solution of sodium chromate is acidified with sulfuric acid (H_2SO_4) Chromate ions are converted to orange dichromate ions.

$2 N a_{2} C r O_{4} + H_{2} S O_{4} \to N a_{2} C r_{2} O_{7} + N a_{2} S O_{4} + H_{2} O$
Conversion of Sodium Dichromate to Potassium Dichromate:

Potassium chloride (KCl) is added to the solution of sodium dichromate. Sodium dichromate is highly soluble, while potassium dichromate is less soluble and precipitates out.

$N a_{2} C r_{2} O_{7} + 2 K Cl \to K_{2} C r_{2} O_{7} ↓ + 2 N a Cl$

Properties

Oxidizing Nature:(K_2Cr_2O_7) acts as a strong oxidizing agent in acidic medium. The chromium(VI) is reduced to chromium(III).

$C r_{2} O_{7}^{2 -} + 14 H^{+} + 6 e^{-} \to 2 C r^{3 +} + 7 H_{2} O (E^{\circ} = + 1.33 V)$

One mole of K₂Cr₂O₇ accepts 6 electrons, so its equivalent weight is 6Molar Mass.
Action of Alkali: In an alkaline medium, the orange dichromate ion converts to the yellow chromate ion. This reaction is reversible and pH-dependent.

$C r_{2} O_{7}^{2 -} (Orange) + 2 O H^{-} ⇌ 2 C r O_{4}^{2 -} (Yellow) + H_{2} O$
Reaction with Halides: In an acidic medium, it oxidizes iodide ions to iodine and bromide ions to bromine.

$C r_{2} O_{7}^{2 -} + 14 H^{+} + 6 I^{-} \to 2 C r^{3 +} + 3 I_{2} + 7 H_{2} O$

3.0Potassium Permanganate KMnO₄

Potassium permanganate is a powerful oxidizing agent that exists as a dark purple crystalline solid.

Preparation from Pyrolusite Ore (MnO_2)

The industrial preparation of KMnO4 is also a multi-step process:

Fusion of Pyrolusite Ore to Potassium Manganate:

$2 M n O_{2} + 4 K O H + O_{2} fusion 2 K_{2} M n O_{4} (green) + 2 H_{2} O$

Finely powdered pyrolusite ore is fused with potassium hydroxide (KOH) and an oxidizing agent like potassium nitrate (KNO_3). Manganese(IV) is oxidized to green manganate(VI) ion.

Oxidative Electrolysis of Potassium Manganate:

The green solution of potassium manganate is electrolytically oxidized. Manganate(VI) ions are converted to permanganate(VII) ions at the anode.
$A t A n o d e : M n O_{4}^{2 -} \to M n O_{4}^{-} + e^{-}$
$A tC a t h o d e : 2 H_{2} O + 2 e^{-} \to H_{2} + 2 O H^{-}$
The green solution turns purple due to the formation of permanganate ions.

Properties

Oxidizing Nature: The oxidizing power of KMnO₄depends on the medium (acidic, basic, or neutral).
Acidic Medium: It is a powerful oxidizing agent. Manganese(VII) is reduced to manganese(II).

$M n O_{4}^{-} + 8 H^{+} + 5 e^{-} \to M n^{2 +} + 4 H_{2} O (E^{\circ} = + 1.51 V)$

One mole of KMnO₄ accepts 5 electrons, so its equivalent weight is 5Molar Mass.
Neutral or Faintly Alkaline Medium: Manganese(VII) is reduced to manganese(IV).

$M n O_{4}^{-} + 2 H_{2} O + 3 e^{-} \to M n O_{2} ↓ + 4 O H^{-}$

One mole of KMnO₄ accepts 3 electrons.
Strongly Alkaline Medium: Manganese(VII) is reduced to manganese(VI).

$M n O_{4}^{-} + e^{-} \to M n O_{4}^{2 -}$

One mole of KMnO₄ accepts 1 electron.
Colour: KMnO₄ solutions are intensely purple due to the charge transfer spectrum. It does not show d-d transition because Mn has a d0 configuration in the MnO_4^- ion.

4.0Key Differences Between K₂Cr₂O₇ and KMnO₄

Feature	Potassium Dichromate (K₂Cr₂O₇)	Potassium Permanganate (KMnO₄)
Colour	Orange	Dark Purple
Oxidizing Power	Strong in acidic medium only	Strong in all medium (acidic > neutral > alkaline)
Reduction Product	Cr^{3+} (Green) in acidic medium	Mn^{2+} (Colourless) in acidic medium, (MnO_2) (Brown) in neutral/alkaline medium
Equivalent Weight	Molar mass / 6 (in acidic medium)	Molar mass / 5 (in acidic medium)
Preparation	From chromite ore (FeCr_2O_4)	From pyrolusite ore (MnO_2)

Frequently Asked Questions (FAQs)

What are the colors of K₂Cr₂O₇ and KMnO₄?

Which is a stronger oxidizing agent in acidic medium?

How is K₂Cr₂O₇ prepared from chromite ore?

Can K₂Cr₂O₇ react with bases?

Frequently Asked Questions (FAQs)

What are the colors of K₂Cr₂O₇ and KMnO₄?

Which is a stronger oxidizing agent in acidic medium?

How is K₂Cr₂O₇ prepared from chromite ore?

Can K₂Cr₂O₇ react with bases?

Join ALLEN!

Potassium Dichromate and Potassium Permanganate

1.0Potassium Dichromate K₂Cr₂O₇ and Potassium Permanganate KMnO₄

2.0Potassium Dichromate K₂Cr₂O₇

Preparation from Chromite Ore $(F e C r_{2} O_{4})$

Properties

3.0Potassium Permanganate KMnO₄

Properties

4.0Key Differences Between K₂Cr₂O₇ and KMnO₄

Table of Content

Join ALLEN!

Potassium Dichromate and Potassium Permanganate

1.0Potassium Dichromate K₂Cr₂O₇ and Potassium Permanganate KMnO₄

2.0Potassium Dichromate K₂Cr₂O₇

Preparation from Chromite Ore $(F e C r_{2} O_{4})$

Properties

3.0Potassium Permanganate KMnO₄

Properties

4.0Key Differences Between K₂Cr₂O₇ and KMnO₄

Table of Content

Frequently Asked Questions (FAQs)

What are the colors of K₂Cr₂O₇ and KMnO₄?

Which is a stronger oxidizing agent in acidic medium?

How is K₂Cr₂O₇ prepared from chromite ore?

Can K₂Cr₂O₇ react with bases?

Frequently Asked Questions (FAQs)

What are the colors of K₂Cr₂O₇ and KMnO₄?

Which is a stronger oxidizing agent in acidic medium?

How is K₂Cr₂O₇ prepared from chromite ore?

Can K₂Cr₂O₇ react with bases?

Join ALLEN!

Potassium Dichromate and Potassium Permanganate

1.0Potassium Dichromate K2Cr2O7 and Potassium Permanganate KMnO4

2.0Potassium Dichromate K2Cr2O7

Preparation from Chromite Ore (FeCr2​O4​)

Properties

3.0Potassium Permanganate KMnO4

Properties

4.0Key Differences Between K2Cr2O7 and KMnO4

Table of Content

Join ALLEN!

Potassium Dichromate and Potassium Permanganate

1.0Potassium Dichromate K2Cr2O7 and Potassium Permanganate KMnO4

2.0Potassium Dichromate K2Cr2O7

Preparation from Chromite Ore (FeCr2​O4​)

Properties

3.0Potassium Permanganate KMnO4

Properties

4.0Key Differences Between K2Cr2O7 and KMnO4

Table of Content

1.0Potassium Dichromate K₂Cr₂O₇ and Potassium Permanganate KMnO₄

2.0Potassium Dichromate K₂Cr₂O₇

Preparation from Chromite Ore $(F e C r_{2} O_{4})$

3.0Potassium Permanganate KMnO₄

4.0Key Differences Between K₂Cr₂O₇ and KMnO₄

1.0Potassium Dichromate K₂Cr₂O₇ and Potassium Permanganate KMnO₄

2.0Potassium Dichromate K₂Cr₂O₇

Preparation from Chromite Ore $(F e C r_{2} O_{4})$

3.0Potassium Permanganate KMnO₄

4.0Key Differences Between K₂Cr₂O₇ and KMnO₄