Barium sulfate is the inorganic compound with the chemical formula BaSO₄. It is a white crystalline solid that is odorless and insoluble in water. It occurs in nature as the mineral barite, which is the main commercial source of barium and materials prepared from it.
Barium Sulfate has a high density, making it useful as a contrast agent in X-ray imaging procedures. Additionally, it is chemically inert, non-toxic, and has a low solubility, which makes it suitable for use as a filler material in plastics and rubbers to enhance their strength and resistance.
Barium Sulfate (BaSO4) Structure
Barium sulfate (BaSO4) has a crystal lattice structure, the barium (Ba) cations and sulfate (SO4) anions are arranged in a repeating, three-dimensional pattern.
Cations and Anions:
- Barium (Ba): This is a large, positively charged ion (cation) with two positive charges (Ba2+).
- Sulfate (SO4): This is a polyatomic anion (a group of atoms that carries a negative charge). In sulfate (SO4)², four oxygen atoms surround a central sulfur atom.
Ionic Bonding
The structure of Barium sulfate is formed through ionic bonding. The positively charged barium cation (Ba2+) attracts two negatively charged sulfate anions (SO4)².
Arrangement
- Each barium cation is surrounded by twelve sulfate anions in a distorted octahedral geometry. Imagine a cube with one set of opposite faces missing, and that’s the basic shape around the barium ion. The twelve sulfates arrange themselves around the edges and slightly towards the center of this distorted cube.
- Conversely, each sulfate anion is surrounded by four barium cations in a tetrahedral arrangement. This means the four barium ions form a pyramid-like shape around the sulfate ion.
Preparation of Barium Sulfate
Method 1: Using Barium Chloride (BaCl2) and Sulfuric Acid (H2SO4)
This is a widely used method due to the easy availability of the starting materials.
- Reaction:
BaCl2 (aq) + H2SO4 (aq) → BaSO4 (s) + 2HCl (aq)
- Procedure:
- Dissolve a known amount of Barium Chloride (BaCl2) in a beaker of distilled water.
- Slowly add dilute Sulfuric Acid (H2SO4) to the Barium Chloride solution while stirring continuously.
- A white precipitate of Barium Sulfate (BaSO4) will form.
- Continue adding Sulfuric Acid until no further precipitation occurs. This ensures complete reaction.
- Let the mixture settle for some time.
- Filter the precipitate using filter paper and wash it thoroughly with distilled water to remove any residual Barium Chloride or Sulfuric Acid.
- Dry the collected Barium Sulfate in an oven at around 100-110°C.
Method 2: Using Barium Sulfide (BaS) and Sodium Sulfate (Na2SO4)
This method is less common but offers an alternative route for Barium Sulfate preparation.
- Reaction:
BaS (aq) + Na2SO4 (aq) → BaSO4 (s) + Na2S (aq)
- Procedure:
- Dissolve a known amount of Barium Sulfide (BaS) in a beaker of distilled water. Barium Sulfide releases Hydrogen Sulfide gas (H2S) upon dissolving, so perform this step in a fume hood to ensure proper ventilation.
- Prepare a solution of Sodium Sulfate (Na2SO4) in another beaker.
- Slowly add the Sodium Sulfate solution to the Barium Sulfide solution while stirring continuously.
- Similar to method 1, a white precipitate of Barium Sulfate (BaSO4) will form.
- Follow steps 5-7 from method 1 for filtration, washing, drying, and collection of the Barium Sulfate product.
Physical Properties of Barium Sulfate (BaSO4)
- Appearance: White, crystalline solid, often a fine powder
- Molecular Weight: 233.39 g/mol
- Density: Approximately 4.5 g/cm³
- Solubility: It is practically insoluble in water and most common solvents, including alcohol.
- Melting Point: The melting point is around 1580°C.
- Crystal Structure: It has a barium ion surrounded by sulfate ions in a regular octahedral arrangement.
- Boiling Point: The boiling point is approximately 1600°C.
- Melting Point: The melting point of barium sulfate is around 1580°C.
- Refractive Index: The refractive index is approximately 1.638.
- Electrical Conductivity: It is a poor electrical conductor.
- Hardness: Mohs hardness of 3-3.5
- Thermal Stability: Highly stable under normal conditions; decomposes at temperatures above 1580°C
- Hygroscopicity: It does not absorb moisture from the air.
- Particle Size: Variable; can be nanoparticles, fine powder, or larger crystals.
- Opacity: It is highly opaque to X-rays and visible light.
Chemical Properties of Barium Sulfate (BaSO4)
- Molar Mass: The molar mass is approximately 233.39 g/mol.
- Solubility: It is highly insoluble in water, with a solubility product constant (Ksp) of 1.1 × 10−10.
- Reactivity: Barium sulfate is a stable compound that is not reactive with most chemicals.
- Decomposition: It decomposes at high temperatures (above 1580°C) to form barium oxide (BaO) and sulfur dioxide (SO2).
- Reaction with Acids: It reacts with strong acids to form soluble barium salts and sulfuric acid.
- Reaction with Sulfides: It reacts with sulfides to form barium sulfide (BaS) and sulfur.
- Electrochemistry: It is a good insulator and does not conduct electricity.
- pH: The pH of its solution is neutral.
- Oxidation States: It contains barium in the +2 oxidation state and sulfur in the +6 oxidation state.
- Crystal Structure: It has a barium ion surrounded by sulfate ions in a regular octahedral arrangement.
- Oxidation States: Barium: +2
- Thermal Decomposition: It decomposes to barium oxide and sulfur dioxide at high temperatures.
- Chemical Reactions: It reacts with strong acids to form soluble barium salts and sulfuric acid.
- Chemical Bonding: It has ionic bonding between barium and sulfate ions.
- Reduction reaction: It can undergo a violent reaction with reducing agents like aluminum powder
- Non-toxic: Despite the toxicity of soluble barium salts, barium sulfate is non-toxic.
Uses / Application of Barium Sulfate
- Medical Imaging: It is used as a contrast agent in medical imaging, such as X-rays, CT scans, and fluoroscopy, to enhance the visibility of the gastrointestinal tract, including the esophagus, stomach, and intestines.
- Radiation Shielding: Due to its high density and low permeability to X-rays and gamma rays, barium sulfate is used in heavy concrete to create radiation shields.
- Waste Treatment: It is sometimes used to treat wastes containing barium salts to immobilize and detoxify the barium due to its low solubility.
Industrial Applications
- Drilling Fluids: It is used in oil and gas well drilling to increase the density of the drilling fluid, reducing the risk of a blowout.
- Plastic Manufacturing: It is used as a filler in plastics to increase their density for vibrational mass damping applications.
- Copper Casting: It is used as a release material in the casting of copper anode plates to prevent the direct contact of liquid copper with the solid copper mold.
- Photographic Paper Coating: A thin layer of barium sulfate called baryta is coated on photographic paper to increase its reflectiveness and uniformity of blacks.
- Integrating Sphere Coating: It is used to coat the interior of integrating spheres due to its high reflectance and near-Lambertian characteristics.
- Firearms Manufacturing: It is listed as a material acceptable by the Bureau of Alcohol, Tobacco, Firearms and Explosives (BATFE) to achieve compliance with X-ray machine requirements for depicting the shape of plastic firearms or components.