Potassium Dichromate and Potassium Permanganate

Dhristi JEE 2022-24

What is Potassium Dichromate?

Potassium dichromate, better known as anhydrochromate, can be prepared by applying neutral yellow chromate of potassium to the solution, which is a moderate volume of one of the stronger acids. Commercially, potassium permanganate is prepared by mixing the potassium hydroxide solution and powdered manganese oxide with oxidizing agents such as potassium chlorate.

Preparation of Potassium Dichromate – K2Cr2O7

Potassium dichromate is an essential chemical that is used in industries as an oxidizing agent and for the preparation of several other compounds.

Usually, dichromates are prepared from chromates, and this is obtained with the combination of chromite ore, including potassium or sodium carbonate, in the presence of air.

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The chemical reaction can be given as follows:

\[4FeCr_2O_4 + 8Na_2CO_3 + 7O_2 \rightarrow 8Na_2CrO_4 + 2Fe_2O_3 + 8CO_2\]

The sodium chromate (Na2CrO4) solution is further purified with sulphuric acid to produce a solution, where the crystals of orange-coloured sodium dichromate (Na2Cr2O7.2H2O) are extracted.

\[2Na_2CrO_4 + 2H^+ \rightarrow Na_2Cr_2O_7 + 2Na^+ + H_2O\]

Now, the potassium dichromate is obtained by reacting a sodium dichromate solution with potassium chloride. The chemical reaction can be given as follows:

\[Na_2Cr_2O_7 + 2KCl \rightarrow K_2Cr_2O_7 + 2NaCl\]

Therefore, we can finally obtain the orange crystals of potassium dichromate.

Structure of Potassium Dichromate Molecules

Potassium dichromate is described as an ionic compound that contains one dichromate anion and two potassium cations. The coordination geometries present around the chromium atoms are tetrahedral. Potassium dichromate’s structure molecule can be illustrated as follows:

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It should also make a note that in the potassium dichromate molecule, potassium shows a+1 oxidation state, and oxygen shows a -2 oxidation state, and chromium shows a+6 oxidation state. It should also make a note that the potassium dichromate crystals have a triclinic structure.

Preparation of Potassium Permanganate – KMnO4

We can get this Potassium Permanganate (KMnO4) by reacting the MnO2 element with an alkali metal hydroxide and the KNO3 (oxidizing agent).

This will further result in the dark green K2MnO4 production, which is disproportionate in a neutral or acidic medium to produce permanganate.

\[3MnO_2^{−4} + 4H^+ \rightarrow 2MnO^{−4} + MnO_2 + 2H_2O\]

\[2MnO_4 + 4KOH + O_4 \rightarrow 2K_2MnO_4 + 2H_2O\]

Thus, the potassium permanganate preparation involves a reaction of MnO2 with KOH to produce MnO2−4 followed by electrolytic oxidation of manganate to produce permanganate ion, MnO2−4.

After this manganese ion, the salt will be oxidized by peroxodisulphate to permanganate ion according to the reaction given as follows:

\[2Mn^{2+} + 5S_2O_2^{−8} + 8H_2O \rightarrow 2MnO^{−4} + 10SO_2^{ −4} + 16H^+ \]

Hence, the potassium permanganate’s dark purple coloured crystals are obtained. The chemical reaction for the same can be given as follows:

\[2KMnO_4 \rightarrow K_2MnO_4 + MnO_2 + O_2\]

Properties of Potassium Dichromate, K2Cr2O7

Potassium dichromate, on heating, decomposes to produce the chromic oxide, oxygen, and potassium chromate. The chemical reaction can be given as follows:

\[4K_2Cr_2O_7 \rightarrow 4K_2CrO_4 + 2CrO_3 + 3O_2\]

  • It is described as a powerful oxidizing agent, and it oxidizes iodide to iodine. The chemical reaction can be given as follows:

\[Cr_2O_2^{−7} + 14H^+ + 6l^− \rightarrow  2Cr^{3+} + 7H_2O +3l_2 \]

  • The compound contains bright red crystals, and it can be used for staining, tanning, dyeing, and more.

  • For medical purposes, it can be antiseptic, caustic, and astringent. When heated, it emits toxic chromium fumes.

  • It is a strong oxidizing agent and highly corrosive for which it can be used in wood preservatives, manufacturing of pigments, and photochemical processes.

Properties of Potassium Permanganate, KMnO4

Potassium permanganate, when heated, produces manganese dioxide, oxygen, and potassium manganate. The chemical reaction can be given as follows:

\[2KMnO_4 \rightarrow K_2MnO_4 + MnO_2 + O_2\]

  • It can be defined as a powerful oxidizing agent in alkaline or acidic solutions.

  • It is noncombustible but works as a catalyst in the burning of combustible materials.

  • It is in purple crystals form and is soluble in hot water.

  • In high concentration, it can become toxic.

  • When mixed with glycerine, it will start a fire.

Applications of Potassium Dichromate

The major application of K2Cr2O7 is in the potassium chrome alum preparation, a compound, which is extensively used in leather tanning. Chromic acid is also prepared from this compound. Also, potassium dichromate is well-known to be used in cement production since it improves the texture and the cement mixture density. 

Another important and major application of potassium dichromate is given in the industry of photography, where it can be used in combination with a powerful mineral acid as an oxidizing agent in photographic screen printing. Since it is non-hygroscopic in nature, potassium dichromate is also employed for many wet tests in the analytical chemistry field.

Use of Potassium Dichromate

It can be used in several applications as an oxidizing agent and also used in different product preparations such as paints, waxes, glues, and more items. Potassium dichromate is highly toxic and carcinogenic as a hexavalent chromium compound.

The critical distinction between potassium permanganate and potassium dichromate is that potassium permanganate has a dim purple tone, while potassium dichromate has a red-orange tone.

Potassium permanganate and potassium dichromate are exceptionally normal in research centers since we regularly use them in titration methods. Albeit these two mixtures contain potassium as a constituent, we can undoubtedly recognize them simply by checking them since they have a totally different appearance.

What is Potassium Permanganate?

Potassium permanganate is an inorganic compound which has the substance recipe KMnO4. Along these lines, the compound is a salt of potassium since it has the two particles, K+ and MnO4–. The metal manganese is in +7 oxidation state. The compound exists in the strong state at room temperature and shows up as a dim purple strong compound. Furthermore, it is a significant medicine to clean injuries.

Key Difference - Potassium Permanganate versus Potassium Dichromate

Also, potassium permanganate is a solid oxidizing specialist. It is water solvent, and after dissolving in water, it gives pink or purple shaded arrangements. The dissipation of water from this arrangement gives dull purple, flickering precious stones.

Besides, this compound is a solid oxidant that doesn't deliver any harmful side-effects. In this way, it is extremely valuable in various applications. The fields of utilization incorporate medication, water treatment, union of natural mixtures, organic product safeguarding, and so forth

What is Potassium Dichromate?

Potassium dichromate is an inorganic compound having the synthetic equation K2Cr2O7. The compound has a splendid, red-orange appearance. Likewise, it is an oxidizing specialist. Hence, there are numerous utilizations of this compound. Nonetheless, as like numerous chromium compounds, potassium dichromate also is intensely hurtful to our wellbeing.

Distinction between Potassium Permanganate and Potassium Dichromate

Coming to creation, there are two methods for delivering potassium dichromate. One is through the response between potassium chloride and sodium dichromate. The subsequent strategy is by cooking the chromate mineral with potassium hydroxide.

Besides, potassium dichromate promptly disintegrates in water, and upon disintegration, it goes through ionization. While considering the applications, it is utilized as a forerunner for potassium chrome alum (a synthetic utilized in the calfskin industry). Other than that, it is additionally utilized for cleaning purposes, in developments, in photography, and so forth

What is the Difference between Potassium Permanganate and Potassium Dichromate?

Potassium permanganate is an inorganic compound which has the synthetic recipe KMnO4 while potassium dichromate is an inorganic compound having the substance equation K2Cr2O7. The vital contrast between potassium permanganate and potassium dichromate is that potassium permanganate has a dim purple tone, while potassium dichromate has a red-orange tone. While considering the oxidation conditions of the metal iotas in these mixtures, manganese in potassium permanganate has +7 oxidation state where chromium in potassium dichromate has +6 oxidation state.

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FAQs (Frequently Asked Questions)

1. What does the potassium dichromate test use?

Potassium dichromate is an oxidizing agent for organic chemistry that is milder than potassium permanganate. It can be used for alcohol oxidation, where this converts the primary alcohols into aldehydes and carboxylic acids under the conditions having more pressure.

2. Is potassium dichromate light-sensitive?

potassium dichromate is light-sensitive and clear orange crystals. It can be used as chromium mordant in cotton dyeing. Potassium dichromate can also be used as an intensifier in black and white image processing.

3. What is the charge of potassium dichromate?

The molecular formula of potassium dichromate can be given as K2Cr2O7. A few of the physical properties of potassium dichromate are: it is a solid reddish-brown colour having a molecular weight of 294.18 grams per mole. This compound is also referred to as a compound of chromium oxidation and hexavalent chromium

4. Why is KMnO4 defined as a self indicator?

The solution loses its pink colour after all the permanganate ions are used up in the chemical reaction. It is meant by the end of the reaction, and thus potassium permanganate is known as self-indicator as it acts as an indicator besides being one of the reactants.