STRONTIUM HYDROXIDE (SR (OH) ₂): STRUCTURE, PROPERTIES, USES - CHEMISTRY - 2025

The strontium hydroxide (Sr (OH) ₂) is an inorganic chemical compound consisting of a strontium ion (Sr) and two hydroxide ions (OH). This compound is obtained by combining a strontium salt with a strong base, resulting in an alkaline compound whose chemical formula is Sr (OH) ₂.

Generally, for the preparation of strontium hydroxide, sodium hydroxide (NaOH) or potassium hydroxide (KOH) is used as a strong base. On the other hand, the strontium salt (or strontium ion) that reacts with the strong base is strontium nitrate Sr (NO ₃) ₂ and the process is described by the following chemical reaction:

2KOH + Sr (NO ₃) ₂ → 2KNO ₃ + Sr (OH) ₂

In solution, the strontium cation (Sr ⁺) comes into contact with the hydroxide anion (OH ^-) forming a basic ionic salt of strontium. Since strontium is an alkaline earth metal, strontium hydroxide is considered a caustic alkali compound.

Obtaining

In addition to the process previously explained, it can be said that once the reaction is carried out, Sr (OH) ₂ precipitates from the solution. Then it is subjected to the washing and drying process, finally obtaining a very fine white powder.

An alternative method for obtaining strontium hydroxide is by heating strontium carbonate (SrCO ₃) or strontium sulfate (SrSO ₄) with steam at a temperature ranging between 500 ° C and 600 ° C. The chemical reaction occurs as shown below:

SrCO ₃ + H ₂ O → Sr (OH) ₂ + CO ₂

SrS + 2H ₂ O → Sr (OH) ₂ + H ₂ S

Chemical structure and physicochemical properties

Currently, 3 forms of strontium hydroxide are known: octahydrate, monohydrate and anhydrous.

Strontium hydroxide octahydrate

Strontium hydroxide precipitates in octahydrate form from solutions under normal conditions of temperature and pressure (25 ° C and 1 atm), whose chemical formula is Sr (OH) ₂ ∙ 8H ₂ O.

This compound has a molar mass of 265.76 g / mol, a density of 1.90 g / cm and precipitates as tetragonal crystals (with space group P4 / ncc) with a quadrangular and colorless prismatic appearance.

Also, strontium hydroxide octahydrate has the ability to absorb atmospheric moisture, as it is an easily deliquescent compound.

Strontium hydroxide monohydrate

According to optical microscopy studies (carried out using the X-ray diffraction technique), by raising the temperature to about 210 ° C -at a constant atmospheric pressure- Sr (OH) ₂ ∙ 8H ₂ O is dehydrated and transformed into Strontium hydroxide monohydrate (Sr (OH) ₂ ∙ H ₂ O).

This form of the compound has a molar mass of 139.65 g / mol and its melting temperature is -73.15 ° C (375K). Due to its atomic configuration, it has less solubility in water than that described in its octahydrate form.

Anhydrous Strontium Hydroxide

By continuing to increase the temperature of the system to about 480 ° C, the dehydration is prolonged until obtaining an anhydrous strontium hydroxide.

Unlike its hydrated forms, it has a molar mass of 121.63 g / mol and a density of 3.625 g / cm ³. Its boiling point is reached at 710 ° C (1,310 ° F or 983 K) while the melting point is at 535 ° C (995 ° F or 808 K).

By Andif1, from Wikimedia Commons

Solubility

Strontium hydroxide octahydrate has a solubility in water of 0.91 grams per 100 milliliters (measured at 0 ° C), while its anhydrous form at similar temperature conditions has a solubility of 0.41 grams per 100 milliliters.

Similarly, this substance is considered insoluble in acetone and fully soluble in acids and ammonium chloride.

Chemical reactivity

Strontium hydroxide is not flammable, its chemical reactivity remains stable at moderate temperatures and pressures, and it is capable of absorbing carbon dioxide from atmospheric air, transforming it into strontium carbonate.

In addition, it is a severely irritating compound if it comes into contact with the skin, respiratory tract or other mucous areas of the body.

Applications

Due to its hygroscopic characteristics and basic properties, strontium hydroxide is used for different applications in industry:

• Extraction of molasses and refining of sugar from beets.
• Plastics stabilizer.
• Greases and lubricants.

Extraction of molasses and refining of beet sugar

At the beginning of the 21st century, strontium hydroxide began to be used in Germany for the refining of sugar from beets through the process patented by Carl Scheibler in 1882.

This procedure consists of the mixture of strontium hydroxide and the sugar pulp of the beet, which results in an insoluble disaccharide. This solution is separated by decantation and once the refining process has been carried out, the sugar is obtained as a final product.

Despite the fact that this procedure is still used today, there are other methods with much more demand, because they are cheaper, which are used in the vast majority of sugar refineries in the world. For example, the Barsil method, which uses Barium silicate or the Steffen method using Cal as an extracting agent.

Strontium fats

They are lubricating greases that contain strontium hydroxide. They are capable of strongly adhering to surfaces with metallic characteristics, are resistant to water and withstand sudden changes in temperature.

Due to their good physical and chemical stability, these greases are used as industrial lubricants.

Plastics stabilizer

The vast majority of plastics, when exposed to climatic factors such as the sun, rain and atmospheric oxygen, modify their properties and deteriorate.

Due to its considerable resistance to water, strontium hydroxide is added to these polymers -during the melting phase- acting as a stabilizer in the manufacture of plastic products to prolong their useful life.

Other apps

• In the paint industry it is used as an essential additive to accelerate the drying process in commercial and industrial paints.
• Strontium salts or ions are obtained from strontium hydroxide, which are used as raw material for the production of pyrotechnic articles.

References

1. Wikipedia. (nd). Strontium hydroxide. Recovered from en.wikipedia.org
2. PubChem. (sf). Strontium Hydroxide. Retrieved from pubchem.ncbi.nlm.nih.gov
3. Lambert, I. and Clever, HL (2013). Alkaline Earth Hydroxides in Water and Aqueous Solutions. Recovered from books.google.co.ve
4. Krebs, RE (2006). The History and Use of Our Earth's Chemical Elements: A Reference Guide. Obtained from books.google.co.ve
5. Honeywell. (sf). Strontium Hydroxide Octahydrate. Recovered from honeywell.com