Sodium chromate (also known as sodium chromate) is an inorganic compound that can be denoted by the formula Na2CrO4. Sodium Chromate is an odorless yellow crystalline chemical that is primarily used in the production of chemicals, inks, and paints, as well as as a wood preservative. In the petroleum industry, sodium chromate is a poisonous and carcinogenic chemical molecule used as a corrosion inhibitor.
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Key Terms- Sodium Chromate, Na2CrO4, Orthorhombic Crystalline Structure, Oxidizer, Sodium ion, Chromium, Molar Mass
Formula And Structure Of Sodium Chromate
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With a molar mass of 161.97 g/mol, sodium chromate has the chemical formula Na2CrO4.
- It's a salt composed of two sodium cations (Na+) and the chromate anion (CrO4-), which has four oxygen atoms connected to the chromium atom.
- In the chromate salt, the oxidation state of chromium is +6. An orthorhombic crystalline structure exists in the solid substance.
Structure of Sodium Chromate
Preparation Of Sodium Chromate
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Sodium chromate is made from stainless steel dinnerware or cooking equipment with at least 10.5 percent chromium by mass.
- The stainless steel is first completely dissolved in concentrated hydrochloric acid. Because of the chromium(III) ion in the solution, it should be dark green. To neutralize all remaining acids and precipitate a mixture of iron and chromium hydroxides, sodium carbonate (not sodium hydroxide) is added to the solution, which is then filtered and washed.
- The cleaned mixture is added to a solution of sodium hypochlorite, which oxidizes the chromium(III) ions to chromate (CrO42-) ions and dissolves them as sodium chromate.
- The sodium chromate is recrystallized from the solution, which is then dried in a desiccator.
Physical Properties Of Sodium Chromate
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Here are some physical properties of Sodium Chromate-
- Sodium chromate is a hygroscopic yellow crystalline substance (that absorbs water from the air).
- It is an odorless solid with a density of 2.7 g/mL and a melting point of 792 degrees Fahrenheit.
- Tetrahydrate (Na2CrO4.4H2O), hexahydrate (Na2CrO4.6H2O), and decahydrate (Na2CrO4.10H2O) versions are also available.
Chemical Properties Of Sodium Chromate
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The hygroscopic sodium chromate solid absorbs water quickly and converts to hydrated salts. Yellow chromate ions are formed when it dissolves in water. The oxidizing agent sodium chromate is mild. It easily combines with acids to produce sodium dichromate, which is a useful industrial chemical.
Sodium Chromate Through Ferrochrome Electrochemical Oxidation
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| Sodium Nitrate Formula | Sodium Hypochlorite Formula | Sodium Peroxide Formula |
| Sodium Acetate | Sodium Borate | Sodium Chlorate |
Handling Of Sodium Chromate
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Ingestion or inhalation of sodium chromate, like all hexavalent chromium compounds, is extremely poisonous and carcinogenic.
- It can cause dermatitis if handled without gloves, and it can also be absorbed through the skin in small amounts, especially if moist.
- Most materials are notorious for discoloration when exposed to aqueous fluids.
When handling it as a powder, always use gloves and goggles, and a dust mask or respirator to avoid inhaling it, which can be lethal.
Also Read- Sodium Dichromate
Storage And Disposal Of Sodium Chromate
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Sodium chromate should be stored in tightly-sealed bottles with a warning label and a hazard symbol.
With a reducing agent such as ascorbic acid or potassium/sodium sulfites/metabisulfites/thiosulfate, sodium chromate can be safely reduced to the less hazardous Cr(III) oxide.
Also Read-
| Sodium Potassium Tartrate | Sodium Silicate | Sodium Sulfate |
| Sodium Thiosulfate | Structure of Chlorate | Chromium III Chloride |
Uses Of Sodium Chromate
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Here are some common uses of Sodium Chromate-
- The production of sodium dichromate (an important precursor to most chromium compounds) and the extraction of chromium metal from its ores are the two main uses of sodium chromate.
- Corrosion control, pigment formulations, wool dyeing, wood preservation, drilling fluids, catalysts, and as an oxidant in organic synthesis are among its numerous uses.
Also Read- Sodium Dihydrogen Phosphate
Things To Remember
- Sodium Chromate is an inorganic compound.
- Sodium chromate is corrosive and oxidizing, and yellow in color.
- Formula of Sodium Chromate is Na2CrO4
- Sodium chromate is primarily harmful to the respiratory system, causing ulcers, shortness of breath, bronchitis, pneumonia, and asthma.
- This substance is a known human carcinogen linked to an increased risk of lung cancer and sinonasal cavity cancer.
Solved Questions
Ques. Why is sodium chromate such a powerful oxidizer? (3 Marks)
Ans. When elements come into contact with sodium chromate in a chemical reaction, they become more electronegative as the oxidation state of their atoms increases. Because it contains chromium in the +6 oxidation state, it is poisonous. It can be converted to harmless chromium in the +3 oxidation state by reacting with a reducing agent. Na2CrO4 is its chemical formula.
Ques. What is the process for making sodium chromate? (2 Marks)
Ans. It's made in a lab by heating chromium ores like chromite (Fe(CrO2)2) and sodium carbonate in the air. The iron oxide is easily separated from the water-soluble sodium chromate.
Ques. Is sodium chromate water soluble? (1 Mark)
Ans. The yellow crystalline solid sodium chromate is dissolved in a liquid media, most likely water. It is water-soluble.
Ques. Is it true that sodium chromate is a precipitate? (2 Marks)
Ans. The majority of silver compounds are insoluble, while almost all alkali metal compounds and nitrates are soluble (except for acetates, perchlorates, chlorates, and nitrates). When soluble silver nitrate and sodium chromate are combined, insoluble silver chromate develops and precipitates.
Ques. Why Is Sodium Chromate Yellow? (2 Marks)
Ans. The yellow chromate ion and the orange dichromate ion are in equilibrium in an aqueous solution. When sodium hydroxide is added to the potassium chromate solution, it turns from orange to yellow. When sodium hydroxide reacts with hydrogen ions, they are eliminated from the solution.
Ques. What are the risks of sodium chromate to one's health? (3 Marks)
Ans. Respiratory discomfort similar to asthma and nasal septal perforation can be caused by inhaling sodium dichromate (VI) dust or mist. It causes diarrhea and vomiting if it is swallowed. It causes dermatitis and local irritation when it is introduced to the eyes and skin.
Although sodium dichromate is a non-combustible substance, it aids in the combustion of other substances. When it comes into contact with other flammable materials, it can explode and catch fire.
Ques. What are the uses of sodium chromate? (5 Marks)
Ans. Apart from its usage in the production of other chromium compounds, sodium dichromate has a wide range of applications as a component in the manufacture of the following materials:
- Metallic Finish - it prevents corrosion, makes cleaning metallic surfaces easier, and allows the paint to adhere.
- Organic materials are employed in the synthesis of vitamin K and wax as oxidizers.
- Inorganic chromate pigments are made with pigments that provide a range of light-stable colors. In undercoats and primers, certain grades of chromate are employed to prevent corrosion.
- Ceramics are used to make colored glass and glaze for ceramics.
- Textiles - used in acidic dyes as a mordant to improve color fastness.
- It's used to make chromium sulfate.
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