Barium hydroxide (Ba(OH)₂): Structure, Properties & Uses

Barium hydroxide, also known as baryta, is a chemical compound with the formula Ba(OH)2. It has a unique structure that influences its properties and behavior. In its solid state, barium hydroxide crystallizes as an octahydrate, Ba(OH)2·8H2O, which can be converted to the monohydrate by heating in air. The octahydrate form is a white crystalline solid.

It is an alkali metal hydroxide, which means its nature is fundamentally basic. Upon dissolving in water, it undergoes an exothermic reaction, liberating heat and forming barium ions (Ba2+) and hydroxide ions (OH-).

The compound is used in various industries, including the production of barium salts, ceramics, pH regulators, and manufacturing of lubricating oils and greases. Barium hydroxide is also used in analytical chemistry for the titration of weak acids, as well as in organic chemistry as a strong base in the hydrolyzation and preparation of other compounds.

Physical Properties of Barium hydroxide (Ba(OH)₂)

  • Molar mass: 171.34 g/mol (anhydrous), 189.355 g/mol (monohydrate), 315.46 g/mol (octahydrate)
  • Appearance: White solid
  • Density: 3.743 g/cm3 (monohydrate), 2.18 g/cm3 (octahydrate, 16 °C)
  • Melting point: 78 °C (octahydrate), 300 °C (monohydrate), 407 °C (anhydrous)
  • Boiling point: About 780 °C, although does not have a well-defined boiling point, as it decomposes before boiling.
  • Solubility: It is moderately soluble in water. At 20°C, approximately 3.89 grams of Ba(OH)₂ can dissolve in 100 grams of water.
  • Crystal Structure: It crystallizes in a monoclinic structure in its anhydrous form.

Chemical Properties of Barium hydroxide (Ba(OH)₂)

  • When barium hydroxide is dissolved in water, it undergoes an exothermic reaction, releasing heat and forming barium ions (Ba2+) and hydroxide ions (OH-) in solution.
  • PH: The solution of barium hydroxide in water is strongly alkaline, with a pH around 12-13 for a 0.1 M solution. Ba(OH)2​→Ba2++2OH−
  • Reaction with Acids: Barium hydroxide reacts with acids to neutralize them and form barium salts and water. Ba(OH)2​+2HCl→BaCl2​+2H2​O
  • Reaction with Carbon Dioxide: Barium hydroxide reacts with carbon dioxide (CO₂) to form barium carbonate (BaCO₃) and water. Ba(OH)2​+CO2​→BaCO3​+H2​O
  • Reaction with Ammonium Salts: Barium hydroxide reacts with ammonium salts, releasing ammonia gas (NH₃). Ba(OH)2​+2NH4​Cl→BaCl2​+2NH3​+2H2​O
  • Precipitation of Metal Hydroxides: Barium hydroxide can precipitate hydroxides of other metals from their aqueous solutions due to the high pH it generates.
  • Thermal Decomposition: Upon heating, barium hydroxide decomposes into barium oxide (BaO) and water vapor. Ba(OH)2​->BaO+H2​O
  • Conductivity: Being a strong base, Ba(OH)₂ solutions exhibit high electrical conductivity due to the dissociation into Ba²⁺ and OH⁻ ions.

Barium hydroxide (Ba(OH)₂) Structure

Barium hydroxide has a layered structure where the Ba centers adopt a square antiprismatic geometry. Each Ba center is bound by two water ligands and six hydroxide ligands, which are respectively doubly and triply bridging to neighboring Ba centers.

The structure of barium hydroxide can be broken down into its constituent ions. The barium ion (Ba2+) has a +2 charge and is surrounded by eight hydroxide ions (OH-) in the octahydrate form. Each hydroxide ion, in turn, consists of an oxygen atom (O2-) covalently bonded to a hydrogen atom (H+).

The octahydrate structure of barium hydroxide can be represented as:

Ba(OH)2·8H2O = [Ba(OH)2]·[8(H2O)]

In this structure, the barium ion is octahedrally coordinated by eight hydroxide ions, forming a complex structure with a high degree of hydration.

When barium hydroxide is dissolved in water, it undergoes an exothermic reaction, releasing heat and forming barium ions (Ba2+) and hydroxide ions (OH-) in solution. This increases the pH of the solution and makes barium hydroxide a strong base.

Preparation of Barium hydroxide (Ba(OH)₂)

One common method involves dissolving barium oxide (BaO) in water. This reaction is highly exothermic, meaning it releases a significant amount of heat. The reaction can be represented as:

BaO + H2O → Ba(OH)2

Another method of preparation involves the reaction of barium chloride (BaCl2) with sodium hydroxide (NaOH). This method is also used to produce barium hydroxide and sodium chloride (NaCl) as byproducts. The reaction can be represented as:

BaCl2 + 2NaOH → Ba(OH)2 + 2NaCl

In a laboratory setting, barium hydroxide is often prepared in an octahydrate form, Ba(OH)2·8H2O. This form is then converted to the monohydrate by heating in air. The octahydrate form is typically used because it is more stable and easier to handle.

To prepare a solution of barium hydroxide, the solid is dissolved in water. For example, to prepare 1000 mL of a 0.1 mol/L solution of barium hydroxide, 31.5462 g of Ba(OH)2·8H2O (100% purity) is dissolved in deionized or distilled water. After the solid is completely dissolved, the solution is diluted to a final volume with deionized (distilled) water.

Uses of Barium hydroxide (Ba(OH)₂)

  • Serves as a precursor for synthesizing various barium compounds, such as barium salts (e.g., barium sulfate, barium carbonate).
  • Employed in organic synthesis for deprotonation reactions and as a catalyst in certain condensation reactions.
  • Used to adjust the pH of water and to remove sulfate ions by precipitating them as barium sulfate (BaSO₄).
  • Acts as an additive in the production of lubricating oils and greases to enhance their stability and performance.
  • Used as a stabilizer in the production of PVC and other plastics, preventing degradation and improving material properties.
  • Used in titrations and other analytical procedures to determine the concentration of acids and other substances.
  • Helps detect the presence of sulfate ions and other anions through precipitation reactions.
  • Used in the refining of sugar from molasses to remove impurities by precipitating them out.
  • Occasionally used to treat acidic soils to raise the pH and improve soil quality for agricultural purposes.
  • It is used in oil-drilling muds and as a component in some types of oil-drilling muds.

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