Education Journalist | Study Abroad Lead
Chromate is a kind of inorganic salt that contains chromium acid and consists of chromic ions/anions.It lies in the category of Inorganic salts and chromate salts contain Chromate anion. Compounds that do not have Carbon-Hydrogen bonds are called Inorganic salts. The oxidation state of Chromate is six plus so it is also called chromium oxyanions. It is a moderately strong oxidizing agent. When protons are separated from chromic acid then it results in these oxyanions. The IUPAC name of Chromate is dioxido or dioxo chromium.
| Table of Content |
Keyterms: Chromate, Inorganic Salt, Ion, Anion, Chromium acid, Carbon, Hydrogen, Chromic acid
Physical properties of Chromate - CrO4-2
[Click Here for Sample Questions]
- Chromate is odorless.
- It is yellowish.
- It is easily soluble in water (H2O).
- It appears as a yellowish powder.
- Its topological surface area is 80.3 a3.
- Its heavy atom count is 5.
- As we know two protons are removed from chromic acid to form a chromate ion, therefore its valency is 2.
Also Read:
| Related Articles | ||
|---|---|---|
| Californium | Chromate | Curium |
| Dichromate | Gadolinium | Inner Transition Elements |
Chemical properties of Chromate - CrO4-2
[Click Here for Sample Questions]
Given below are the chemical properties of chromate:
- The Chemical Formula of Chromate or Chromate Ion formula is CrO42-.
- The Molecular weight or the Molar mass of Chromate is 115.994 g/mol-1.
- The density of chromate ion is 2.73 g/cm3.
Structure of Chromate ion
[Click Here for Sample Questions]
In the diagram below, Chromium has covalent bonds with four oxygen atoms consisting of two single and two double bonds.
The resulting structure is a result of the removal of two protons from the chromic acid.
Chromate Structure - CrO4-2
Chemical reactions of Chromate - CrO4-2
[Click Here for Sample Questions]
- In acidic solution, Chromate ion acts as a strong oxidizing agent, while in alkaline solution Chromate ion combines with water (H2O), and we will observe it forms chromium (III) hydroxide.
CrO42− + 4 H2O + 3 e− → Cr(OH)3 + 5 OH−
- Potassium nitrate and barium chromate can be created by reacting potassium chromate to barium nitrate. Likewise, it can combine with other elements to form various other compounds such as calcium chromate, sodium chromate, ammonium chromate, etc.
K2CrO4 + Ba(NO3)2 ↔ BaCrO4 + 2KNO3
Applications of Chromate - CrO4-2
[Click Here for Sample Questions]
- We all are aware that crayons of children are wax products, but some industrial cement consists of chromate salts that are not at all harmful.
- Yellow crystals of potassium chromate are used as a pigment in dye and inks, it is toxic by ingestion.
- Chromate salts are either dry or in solution form, and don't have any effect on aluminum. Salts with Calcium, Potassium, Sodium, and ammonium are excellent corrosive materials. Its pretreatment layer is used to form the coating depending upon its thickness. These salts act as an adhesive material between metal and primer to prevent them from corrosion. The effect is long-lasting, depletion takes place only in case of a scratch or any other damage to the material. In industries, coating of these salts is deposited on the surface of the material.
- Even though the layer of chromate is harmful to health still it’s used in several products such as enamels, rustproofing materials, etc., which are enforced to this way of corrosion prevention.
- Chromate plating is a process that prevents corrosive materials from corrosion, the items that are used regularly are more likely to form rust or decay, so increasing the longevity of the material could be helped by plating chromium salts.
- When used as oxidizing agents in redox chemical reactions, chromate turns into trivalent chromium salts Cr3+, these salts are of a different bluish-green color.
Natural Occurrence of Chromate CrO4-2
[Click Here for Sample Questions]
- Chromates do occur naturally in several forms on the planet.
- They are present in the desert area and in certain metals (which can be extracted by oxidizing the metal). Deserts such as the Atacama Desert in Chile and also the deserts in Jordan have many Chromate deposits.
- Highly oxidizing species are found in nitrate deposits around the globe. They also have other species such as iodine, perchlorate, bromate, and iodate. The existence is due to the scarcity of organic materials present in nature that enables them to react. These minerals or species have high solubility as they are under the preservation of the desert.
Things to Remember
- The IUPAC name of Chromate is dioxido or dioxo chromium.
- The Chemical Formula of Chromate or Chromate Ion formula is CrO4-2.
- The Molecular weight or the Molar mass of Chromate is 115.994 g/mol-1.
- The density of chromate ion is 2.73 g/cm3.
- In acidic solution, Chromate ion acts as a strong oxidizing agent, while in alkaline solution Chromate ion combines with water (H2O), and we will observe it forms chromium (III) hydroxide.
CrO42− + 4 H2O + 3 e− → Cr(OH)3 + 5 OH−
- Potassium nitrate and barium chromate can be created by reacting potassium chromate to barium nitrate. Likewise, it can combine with other elements to form various other compounds such as calcium chromate, sodium chromate, ammonium chromate, etc.
K2CrO4 + Ba(NO3)2 ↔ BaCrO4 + 2KNO3
Also Read:
Sample Questions
Ques. Chromate is an acid or base? (2 marks)
Ans. The chromate ion is the predominant species in alkaline solutions but in acidic solutions, dichromate can become a predominant ion.
Ques. Is there any difference between chromium and chromate? (2 marks)
Ans. They are similar and not completely different. An acid of chromium called chromic acid loses two protons to form chromate. Chromium is widely used for electroplating and several other processes. Similarly, industries use chromate to prevent rusting and corrosion of materials. So basically the chromates are the modified form of chromium elements.
Ques. What is chromate used for? (2 marks)
Ans. It is mainly used as an inhibitor of corrosion, as a primer, as a decorative finish, or to maintain electrical conductance. The process takes its name from the chromate present in chromic acid, also known as hexavalent chromium, the most commonly used chemical in the immersion bath phase by which the coating is applied.
Ques. How do you make a chromate solution? (2 marks)
Ans. Formulated in yellow chromate. Dissolve the dichromate and the chromic acid first with a little water, then add the nitric and sulphuric and carry the volume with water up to 50 liters to dissolve both.
Ques. What is potassium chromate used for? (2 marks)
Ans. It is used as a fungicide in chemical processing, for making pigments for paints and inks, and for producing other chromium compounds. Potassium chromate is a potassium salt in a ratio of 2:1 consisting of potassium and chromate ions. It has a role as both a carcinogenic and an oxidizing agent.
Ques. Why does chromate have a 2 charge? (2 marks)
Ans. When chromate salt dissociates, we get chromate ions. It consists of one chromium and four oxygen atoms. By adding the oxidation state of chromium and total oxidation state of oxygen, we get -2. So, the ionic charge on chromate ions is -2.
Ques. How do you test for chromate? (2 marks)
Ans. This test involves placing drops of a lead acetate solution on the surface of the product, waiting 5 seconds, and then blotting it gently. If this solution creates a dark deposit or black stain, then there is unpassivated zinc present. A clear result indicates the presence of a chromate passivation coating.
Ques. How do you test for zinc plating? (2 marks)
Ans. With a yellow dichromate coating, the test will determine how well the chromate (color) protects the zinc plating deposit, or how many hours it takes to wear through the chromate which causes the zinc to rust and form its characteristic “white rust”. This is reported as hours to white rust.
Ques. Explain how condensation reactions occur for chromate and dichromate ions? (5 marks)
Ans. All polyoxoanions of chromium (VI) have structures made from tetrahedral CrO4 units sharing corners.
The hydrogen chromate ion, HCrO4−, may be a weak acid:
HCO-4 ⇔ CrO2-4 + H+; pKa ≈ 5.9
It is also in equilibrium with the dichromate ion:
2 HCrO−4 ⇔ Cr2O2−7 + H2O
As a result, this equilibrium doesn’t involve a change in proton concentration, which might predict that the equilibrium is independent of pH. The hydrogen chromate ion could also be protonated, with the formation of molecular acid, H2CrO4, but the pKa for the equilibrium
H2CrO4 ⇔ HCrO−4 + H+
Is not well characterized. Reported values vary between about −0.8 and 1.6.
The dichromate ion may be a somewhat weaker base than the chromate ion.
HCr2O−7 ⇔ Cr2O2 -7 + H+, pK = 1.8
The pK value for this reaction shows that it is often ignored at pH > 4.
For Latest Updates on Upcoming Board Exams, Click Here: https://t.me/class_10_12_board_updates
Check-Out:
Comments