Potassium Chromate Formula: Potassium chromate is an inorganic compound. Its chemical formula is \({{\text{K}}_2}{\text{Cr}}{{\text{O}}_4}.\) The naturally occurring mineral of potassium chromate is tarapacaite. Potassium chromate is the potassium salt of the chromate anion. It is a yellow crystalline solid and the most widely used laboratory chemical. Like potassium dichromate, potassium chromate is also used as an oxidizing agent. In this article, we are going to discuss more on potassium chromate.

Formula of Potassium Chromate

The chemical formula of potassium chromate is \({{\text{K}}_2}{\text{Cr}}{{\text{O}}_4}.\) It contains potassium \(\left({{{\text{K}}^ + }} \right)\) and chromate \(\left( {{\rm{CrO}}_4^{2 – }} \right)\) ions. There is an ionic bond formed between potassium and chromate ions. Hence it is considered as an ionic compound.
Potassium chromate can be represented as,

The chromate ion in potassium chromate has a tetrahedral structure.

The molar mass of potassium chromate is approximately equal to \(194.189\,{\text{g}}/{\text{mol}}.\)

Structure of Potassium Chromate (K₂CrO₄)

The chemical formula of potassium chromate can be derived using the Criss-cross method.

In the criss-cross method, if we know the valency of each element of a compound, we can easily write its formula. The symbol of the positive part is written to the left-hand side and the symbol of the negative part to its right. The valency of each element is placed as a subscript on the side of the symbol of other elements. Subscript \(1\) is not often written.

Using this, the chemical formula of potassium chromate is found as,

Potassium chromate contains potassium \(\left({{{\text{K}}^ + }} \right)\) and chromate \(\left( {{\rm{CrO}}_4^{2 – }} \right)\) radicals. The valency of potassium radical is one and that of chromate radical is two. By criss-crossing these valency numbers, the chemical formula of potassium chromate is \({{\text{K}}_2}{\text{Cr}}{{\text{O}}_4}.\) That is,

Properties of Potassium Chromate \(\left({{{\text{K}}_2}{\text{Cr}}{{\text{O}}_4}} \right)\)

Let us discuss the physical and chemical properties of potassium chromate.

Physical Properties of Potassium Chromate \(\left( {{{\text{K}}_2}{\text{Cr}}{{\text{O}}_4}} \right)\)

1. Potassium chromate appears as a yellow powder.
2. It is highly soluble in water and insoluble in alcohol.
3. It is an odourless compound.
4. The density of potassium chromate is approximately equal to \(2.7320\,{\text{g}}/{\text{c}}{{\text{m}}^3}.\)
5. The melting point of potassium chromate is approximately equal to \(1241\,{\text{K}}\) and its boiling point is approximately equal to \(1270\,{\text{K}}.\)

Chemical Properties of Potassium Chromate \(\left( {{{\text{K}}_2}{\text{Cr}}{{\text{O}}_4}} \right)\)

1. In solutions, the behavior of potassium chromate is similar to that of sodium dichromate.
2. Potassium chromate when treated with lead \(\left({{\text{II}}} \right)\) nitrate, an orange yellow precipitate of lead \(\left({{\text{II}}} \right)\) chromate is formed. The chemical equation for the reaction can be given as,
   \({\text{Pb}}{\left({{\text{N}}{{\text{O}}_3}} \right)_2} + {{\text{K}}_2}{\text{Cr}}{{\text{O}}_4} \to {\text{PbCr}}{{\text{O}}_4}\left({\text{s}} \right) + 2{\text{KN}}{{\text{O}}_3}\)

Preparation of Potassium Chromate \(\left({{{\text{K}}_2}{\text{Cr}}{{\text{O}}_4}} \right)\)

Potassium chromate can be prepared using the following methods:

1. Reaction of Potassium Dichromate with Potassium Hydroxide

Potassium chromate and water are formed when potassium hydroxide is treated with potassium dichromate. The chemical equation for the reaction can be given as,

\({{\text{K}}_2}{\text{C}}{{\text{r}}_2}{{\text{O}}_7}\left({{\text{aq}}} \right) + 2{\text{KOH}} \to 2~{{\text{K}}_2}{\text{Cr}}{{\text{O}}_4} + {{\text{H}}_2}{\text{O}}\)

2. Reaction Between Chromium Oxide and Potassium Hydroxide

When potassium hydroxide and chromium oxide are fused, potassium chromate is obtained. The chemical equation for the reaction can be given as,

\(2{\text{KOH}} + {\text{C}}{{\text{r}}_2}{{\text{O}}_3} \to 2~{{\text{K}}_2}{\text{Cr}}{{\text{O}}_4} + {{\text{H}}_2}{\text{O}}\)

Practice Exam Questions

3. Reaction of Potassium Chromate with Barium Sulphate:

A yellow precipitate of barium chromate is formed when potassium chromate is reacted with barium sulphate solution. The chemical equation for the reaction can be given as,

\({{\text{K}}_2}{\text{Cr}}{{\text{O}}_4} + {\text{BaS}}{{\text{O}}_4} \to {{\text{K}}_2}{\text{S}}{{\text{O}}_4} + {\text{BaCr}}{{\text{O}}_4}\)

4. Reaction of Potassium Chromate with Hydrochloric Acid

Potassium chloride, water and potassium dichromate are formed when potassium chromate reacts with hydrochloric acid. The chemical equation for the reaction can be given as,

\(2\;{{\rm{K}}_2}{\rm{Cr}}{{\rm{O}}_4} + 2{\rm{HCl}} \to {{\rm{K}}_2}{\rm{C}}{{\rm{r}}_2}{{\rm{O}}_7} + 2{\rm{KCl}} + {{\rm{H}}_2}{\rm{O}}\)

5. Reaction of Potassium Chromate with Nitric Acid

Potassium chromate when treated with an excess of dilute nitric acid, potassium dichromate, potassium nitrate and water are formed. The chemical equation for the reaction can be given as,

\(2~{{\text{K}}_2}{\text{Cr}}{{\text{O}}_4} + 2{\text{HN}}{{\text{O}}_3} \to {{\text{K}}_2}{\text{C}}{{\text{r}}_2}{{\text{O}}_7} + 2{\text{KN}}{{\text{O}}_3} + {{\text{H}}_2}{\text{O}}\)

6. Reaction of Potassium Chromate with Silver Nitrate

Potassium Chromate reacts with silver nitrate to form silver chromate and potassium nitrate. The chemical equation for the reaction can be given as,

\(2{\text{AgN}}{{\text{O}}_3}\left({{\text{aq}}} \right) + {{\text{K}}_2}{\text{Cr}}{{\text{O}}_4}\left( {{\text{aq}}} \right) \to {\text{A}}{{\text{g}}_2}{\text{Cr}}{{\text{O}}_4}\left({\text{s}} \right) + 2{\text{KN}}{{\text{O}}_3}\left({{\text{aq}}} \right)\)

The above reaction is an example of a precipitation reaction as well as a double displacement reaction.

Like potassium dichromate, potassium chromate also acts as an oxidizing agent. For example, potassium chromate is used as an oxidizing agent in organic synthesis. It is a carcinogenic agent too.

Uses of Potassium Chromate

The major uses of potassium chromate include:

1. Potassium chromate is used as an oxidizing agent in organic synthesis.
2. It is majorly used as a reagent in chemical laboratories.
3. Potassium chromate is used in qualitative analysis. For example, in colorimetric test for silver ion.
4. Potassium chromate turns red in the presence of excess of silver ions. Therefore, it is used as an indicator in precipitation titrations along with silver nitrate and sodium chloride.
5. Potassium chromate is used in making paints and pigments.
6. It is used for the production of other chromium compounds.
7. Potassium chromate is used as a fungicide.
8. It is also employed in tanning leather and dyeing textiles.

Summary

Potassium chromate is an inorganic compound with the chemical formula \({{\text{K}}_2}{\text{Cr}}{{\text{O}}_4}.\) It is common laboratory chemical. It is a yellow crystalline solid. It can be produced by the reaction of potassium dichromate with potassium hydroxide or by the reaction of potassium hydroxide and chromium oxide. Like potassium dichromate, potassium chromate is also used as an oxidizing agent. The physical and chemical properties and the common uses of potassium chromate are explained in this article.

FAQs on Potassium Chromate

Q.1. What is \({{\text{K}}_2}{\text{Cr}}{{\text{O}}_4}\)?
Ans: \({{\text{K}}_2}{\text{Cr}}{{\text{O}}_4}\) is potassium chromate. It is a yellow crystalline solid.

Q.2. How do you write the formula for potassium chromate?
Ans: Potassium chromate contains potassium \(\left({{{\text{K}}^ + }} \right)\) and chromate \(\left( {{\rm{CrO}}_4^{2 – }} \right)\) radicals. The valency of potassium radical is one and that of chromate radical is two. By criss-crossing these valency numbers, the chemical formula of potassium chromate is \({{\text{K}}_2}{\text{Cr}}{{\text{O}}_4}.\)

Q.3. Why is potassium chromate used as an indicator?
Ans: Potassium chromate turns red in the presence of excess silver ions. Therefore, it is used as an indicator in precipitation titrations along with silver nitrate and sodium chloride.

Q.4. What is potassium chromate used for?
Ans: Potassium chromate has got many uses. They include:
1. Potassium chromate is used as an oxidizing agent in organic synthesis.
2. It is used as a laboratory reagent.
3. It is used as an indicator.
4. It is used for the production of other chromium compounds.
5. Potassium chromate is used as a fungicide.
6. It is also employed in tanning leather and dyeing textiles.

Q.5. What is the difference between potassium chromate and potassium dichromate?
Ans: They are closely related inorganic compounds. Potassium dichromate is \({{\text{K}}_2}{\text{C}}{{\text{r}}_2}{{\text{O}}_7}\) and potassium chromate is \({{\text{K}}_2}{\text{Cr}}{{\text{O}}_4}.\) Potassium dichromate is a red-orange crystalline solid but potassium chromate is a yellow crystalline solid.

Study About Potassium Hydroxide Here

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