Tungstic Acid: Formula, Preparation and Uses

Tungstic acid is a chemical compound with the formula H₂WO₄ or WO₃·H₂O. It is a white or yellowish powder that is soluble in water and has a strong acidic taste. 

• Tungstic acid is a hydrated form of tungsten trioxide, which is the most common commercial form of tungsten.
• Tungstic acid is an important precursor to a wide range of tungsten compounds, including tungsten carbide and tungsten oxide. 
• It is also used as a catalyst in the production of acrylic acid and other organic compounds.
•  In addition, tungstic acid has applications in analytical chemistry, as a reagent for the determination of phosphates and arsenates, and in the preparation of pigments and dyes.

Read More: Acid and Bases

Key Terms: Tungstic acid Formula, Tungstic acid Preparation, Acid of Wolfram, Tungstates

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What is Tungstic Acid

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Tungstic acid has several different crystal structures, including tetragonal, orthorhombic, and monoclinic. Its properties and applications depend on its crystal structure and the conditions under which it is prepared.

• ‘Acid of Wolfram’ is the classical name of tungstic acid.
• Tungstates are the salts of tungstic acid
• It is having a density of 5.5g/cm³
• The melting point of tungstic acid is 100^oC

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Preparation of Tungstic Acid

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Tungstic acid is a chemical compound with the chemical formula H₂WO₄ ,also known as para-tungstic acid. It can be prepared through various methods, including the oxidation of tungsten trioxide, the reaction of sodium tungstate with an acid, and the hydrolysis of tungsten hexachloride.

• Here is a simple method to prepare tungstic acid using sodium tungstate and hydrochloric acid:
• Materials:
  • Sodium tungstate dihydrate (Na₂WO₄.2H₂O)
  • Hydrochloric acid (HCl)
  • Distilled water
  • Glass beaker
  • Stirring rod
  • Filter paper
  • Funnel

Procedure:

• Dissolve 20 grams of sodium tungstate dihydrate in 200 mL of distilled water in a glass beaker. Stir the mixture until the sodium tungstate is fully dissolved.
• Add 50 mL of hydrochloric acid to the sodium tungstate solution. Stir the mixture for a few minutes until the solution becomes cloudy.
• Heat the solution to 70-80°C and continue stirring for 1-2 hours. The solution will gradually turn into a yellow precipitate.
• Allow the solution to cool to room temperature and then filter the precipitate using filter paper and a funnel.
• Wash the precipitate several times with distilled water to remove any remaining impurities.
• Dry the precipitate in an oven at 100°C for several hours until it becomes a dry, white powder.
• Tungstic acid is now ready for use.

Note: The reaction of sodium tungstate with hydrochloric acid generates hydrogen gas, so make sure to perform the reaction in a well-ventilated area.

Read More: List of strong acids

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Tungstic Acid Formula

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Tungstic acid, with the chemical formula H₂WO₄, is a polymeric compound that consists of chains of linked tungsten atoms, each of which is tetrahedrally coordinated to four oxygen atoms. The oxygen atoms are also shared between neighboring tungsten atoms, forming a three-dimensional network of corner-sharing tetrahedra.

Structure of tungstic acid

• In its solid state, tungstic acid exists as a white, amorphous solid powder. In solution, it forms an acidic solution with a pH of around 2.5.
• The structure of tungstic acid can be visualized as a polymer of WO₄ tetrahedra, linked together by shared oxygen atoms. 
• Each tungsten atom is also bonded to two hydroxyl (OH) groups, which contribute to the acidic nature of the compound. 
• The overall structure of tungstic acid resembles that of other polyoxometalates, such as molybdic acid and phosphotungstic acid.

Tungstic acid has a polymeric structure consisting of linked tungsten atoms tetrahedrally coordinated to oxygen atoms, with hydroxyl groups contributing to its acidic properties.

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Properties of Tungstic Acid

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Tungstic acid is a yellowish-white solid compound with the chemical formula H₂WO₄ It is also known as wolframic acid, tungstic (VI) acid, or tungsten acid. Here are some properties of tungstic acid:

• Physical properties: Tungstic acid is a solid substance that has a yellowish-white color. It is odorless and tasteless, and it is insoluble in water.
• Chemical properties: Tungstic acid is a strong oxidizing agent, and it reacts with many substances, such as metals, non-metals, and organic compounds. It can be reduced to tungsten trioxide by heating in a reducing atmosphere.
• Acidic properties: Tungstic acid is a weak acid with a pKa of approximately 1.7. It can donate two protons in solution, forming the tungstate ion (WO₄)^2-.
• Thermal stability: Tungstic acid is stable at room temperature, but it decomposes at higher temperatures, releasing water and forming tungsten trioxide.
• Applications: Tungstic acid is used in the production of tungsten metal and alloys, as well as in the production of catalysts and pigments. It is also used in the chemical industry as an analytical reagent.
• Toxicity: Tungstic acid is generally considered to be of low toxicity, but exposure to high concentrations can cause respiratory and digestive tract irritation. Ingestion or inhalation of large amounts of tungstic acid can cause serious health effects.

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Uses of Tungstic Acid

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Here are some of the uses of tungstic acid:

• Catalyst: Tungstic acid is used as a catalyst in the production of sulfuric acid, which is a widely used industrial chemical. It is also used as a catalyst in the conversion of alkanes to alkenes.
• Pigment: Tungstic acid is used as a yellow pigment in ceramics and other materials.
• Electrochromic devices: Tungstic acid is used in electrochromic devices, such as smart windows and electrochromic mirrors, due to its ability to change color when exposed to an electric current.
• X-ray screens: Tungstic acid is used as a component in X-ray screens and photographic films due to its high density, which allows it to absorb X-rays and other forms of ionizing radiation.
• Tungsten carbide production: Tungstic acid is a key raw material in the production of tungsten carbide, which is used in cutting tools, drilling tools, and other industrial applications.
• Chemical analysis: Tungstic acid is used in chemical analysis as a reagent to test for the presence of various elements, such as copper and tin.

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Things to remember

• Tungstic acid is also known as tungsten trioxide, with the chemical formula H₂WO₄.
• It is a white or yellowish powder that is highly dense and soluble in water and acids.
• Tungstic acid has a variety of industrial applications, including as a catalyst, pigment, and component in electrochromic devices and X-ray screens.
• It is also a key raw material in the production of tungsten carbide, a hard and durable material used in cutting and drilling tools.
• Tungstic acid is generally considered to be non-toxic, although inhalation of its dust may cause respiratory irritation.
• Proper storage and handling of tungstic acid are important to ensure safety and prevent spills or contamination.
• Ongoing research is exploring new applications for tungstic acid and ways to improve existing processes in various industries.