Chromate Ion

In the field of chemistry, chromate falls under the category of inorganic salts. Acids and bases come together to form neutral ionic compounds known as salts. Subsequently, the compounds that do not possess carbon-hydrogen bonds are inorganic salts, and the compounds that have carbon-hydrogen bonds are organic salts. When an acid reacts or acts on a base, then it results in the formation of inorganic salts. In some instances, acids can also react with metals to form inorganic salts. Some great examples of mineral salts are sodium chloride, potassium chloride, calcium chloride etc. Sodium, potassium, and calcium combine with chlorine to form these inorganic salt compounds. Let us consider an acid A and a base B then they combine to form salt AB and release water in the process. 

AH+BOH ---> AB+H2O

They are in the form of granules, powders, or solids at room temperature. Now let us look at chromate as salt, the chromate formula, and chromate ion formula. 

What is Chromate?

Chromate is a type of inorganic salt containing chromic acid consisting of chromate ion(anions). It can be distinguishable by its specific yellowish colour. In addition to that, the oxidation state of chromate is six plus. And hence it is also called chromium oxoanions. When the protons from chromic acid are separated, then it results in these oxoanions. The IUPAC name of chromate is dioxo chromium. Also, chromate has a molecular weight of 194.18 g/mol. Now let us look at the chromate formula or chromate anion formula. The chromate formula for chromate ion formula is CrO42-

Structure of Chromate Ion

To have an in-depth understanding of the structure of the Chromate ion formula, we will have to look at the diagram below. We know that the molecular formula of chromate is CrO42-.

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                                                   ( Structure of Chromate Ion)

In the above diagram, chromium has covalent bonds with four oxygen atoms consisting of two single and two double bonds. This structure is the direct result of the removal of two protons from the chromic acid.  

Physical Properties of Chromate

Chromate has several visible physical properties. Generally, it is easily soluble in water( H2O ). The appearance of chromate is identifiable by the yellowish colour or yellow powder. Chromate is odourless when it comes to odour.  Since two of the protons from chromic acid are removed to form chromate, the valency of chromate is two. It has a topological polar surface area of 80.3. Furthermore, the heavy atom count is five.   

Chemical Properties of Chromate

Chromate has a variety of chemical properties. It also has a variation known as dichromate salts that possess dichromate anion. In acidic solutions, its ion works as a firm oxidizing agent.  Upon combining it with water, we can observe that it forms chromium(III) hydroxide. 

CrO42- + 4H2O + 3e-  ---> Cr(OH)3 + 5OH-

We can create potassium nitrate and barium chromate by reacting potassium chromate (i.e. the combination of potassium and chromate) to barium nitrate.

K2CrO4 + Ba(NO3)2 <---> BaCrO4+ 2KNO3

Similarly,  it combines with other elements to form various new products such as ammonium chromate, sodium chromate, calcium chromate etc. 

Uses of Chromate

There are various uses of chromate. Some of them are:

  • Their salts either in the dry form or solution form, do not have any effect on aluminium. Salts with potassium, sodium, calcium, ammonium act as excellent corrosive materials. We use its pretreatment layer to form its coating depending upon the thickness. The salts act as an adhesive material between metal and primer and prevent it from corrosion. It has a long-lasting effect and only depletes on scratch or other damage to the material. Hence, they possess a self-healing effect alongside their low solubility property. Industries deposit the coatings of these salts upon the surface of the material. Although the layer of chromate can be hazardous for health, we still use it on several products. Products such as rustproofing materials, enamels etc. are subject to this method of corrosion prevention. 

  • The crystals of its salts with other elements such as potassium (mainly yellowish colour) can form pigments for ink or dye. Their oxidizing property, as well as insolubility, makes them perfect for the job. Due to salts being health hazardous, they are highly toxic for health, and no one should consume these products. 

  • You must be aware that the crayons for children are wax products, but some industrial crayons contain chromate salts that are not at all harmless. 

  • A process called chromate plating is used to prevent corrosive materials from corrosion. The items that we use every day are prone to rust and decay, so to increase their longevity plating of salts(chromium) is perfect.

FAQ (Frequently Asked Questions)

1. What Is The Difference Between Chromium And Chromate?

Chromium and chromate are not fundamentally different. They are very much similar. Chromium, also known as chrome is widely in use for electroplating and various other processes. Similarly, industries use chromate to prevent rusting or corrosion from metals by providing a conversion finish—an acid of chromium, also known as chromic acid loses two protons to form chromates. So chromates are simply a modification of chromium elements.    

2. Where Can We Find Chromate On Earth Naturally?

Besides the processes involved in creating chromate by chemical means, there are several other sources as well. Chromate occurs naturally in different forms on the planet. They are present in mainly two areas first is deserts and second in a few metals ( extracting by oxidizing the metal). Deserts such as the Atacama in Chile and deserts in Jordan have significant chromite deposits. We find some of the highly oxidizing species in nitrate deposits around the globe. They also contain some other species such as iodine, perchlorate, iodate and bromate. They mainly exist due to the scarcity of the organic materials present in nature that enables them to react. Also, these minerals or species have high solubility since they are under the preservation of the desert.