Is BaSO4 soluble or insoluble?

Answer: BaSO4 would typically be considered insoluble due to the presence of a sulfate ion. This usually precludes an ion from disassociating easily in an aqueous solution; this being water. 

The idea of BaSO4 being considered insoluble is further borne out in the Ksp values. While these cannot be directly related to molar solubility, they provide a strong hint that Barium sulfate is more stringent than other comparable molecules. For example Ba(OH)2's ksp is approximately seven orders of magnitude less which means that it is much more likely to ionize. You can tell that the molar solubility of barium hydroxide is orders of magnitude greater without performing the necessary calculations. As a reminder a compound is considered insoluble if less than 1% of the compound ionizes. 

Barium Products Ksp Values
ksp values of some common Barium products (source)

What is the molar solubility of BaSO4?

The calculation is based on the chemical equation for the disassociation of BaSO4 and the formula for ksp (equilibrium constants only include aqueous and gaseous species). 

BaSO₄(s) ⇌ Ba²⁺(aq) + SO₄²⁻(aq)

K_sp = [Ba²⁺][SO₄²⁻]

Since when we ionize we create the two ions in equal molar quantity we can state the following

[Ba²⁺] = [SO₄²⁻] = x

$1.1*10^-10 = x^2$

x = $1.05*10^-5$ M

This concentration indicates that less than 1% of the solution is composed of ionized species. 

How does BaSO4 theoretically ionize? 

As the equation (BaSO4 (s) => Ba(2+)(aq) + SO4(2-)(aq)) indicates, barium sulfate would disassociate and produce the barium and sulfate ion. In the real world; however, the low molar solubility indicates that very little barium sulfate actually ionizes. 

What experimental techniques can be utilized in order to verify the solubility of BaSO4?

Experimental observations play a crucial role in confirming the insolubility of barium sulfate. Several methods and techniques are employed to assess the solubility of a compound, and in the case of barium sulfate, the following experimental observations contribute to our understanding of its insolubility:

  1. Precipitation Reaction: One common method to demonstrate the limited solubility of barium sulfate is through a precipitation reaction. When a soluble barium salt (e.g., barium chloride, BaCl₂) is added to a solution containing a soluble sulfate salt (e.g., sodium sulfate, Na₂SO₄), a white precipitate of barium sulfate forms. The appearance of the precipitate indicates that the compound is not fully dissolving in the solution, supporting its insoluble nature.

BaCl₂(aq) + Na₂SO₄(aq) → BaSO₄(s) + 2NaCl(aq)

  1. Gravimetric Analysis: Gravimetric analysis is a quantitative method used to determine the concentration of a particular species in a solution by measuring its mass. In the case of barium sulfate, after precipitating the compound as mentioned above, the collected precipitate is filtered, washed, and dried to remove any remaining soluble impurities. The mass of the resulting dried barium sulfate is then measured, and from the stoichiometry of the reaction, the concentration of dissolved barium ions can be calculated. The extremely small mass of barium sulfate obtained in these experiments is indicative of its low solubility.

  2. Solubility Curves: A solubility curve represents the relationship between temperature and the solubility of a compound. For barium sulfate, a solubility curve can be constructed by determining the concentration of dissolved barium ions at various temperatures. The resulting curve shows that the solubility of barium sulfate is virtually constant over a wide temperature range, consistent with its insoluble nature.

  3. Saturation Point: By adding barium sulfate to water and continuously stirring the mixture, a saturation point is eventually reached where no more solid will dissolve, and any additional barium sulfate added will not disappear into the solution. This point is critical as it shows the maximum concentration of dissolved barium ions that can be achieved, providing further evidence of the compound's limited solubility.

Together, these experimental observations provide strong evidence for the insolubility of barium sulfate in water and support the theoretical understanding derived from the thermodynamics and solubility product constant (K_sp) considerations. The combination of theoretical principles and experimental data reinforces our confidence in the knowledge that barium sulfate is indeed highly insoluble in aqueous solutions.

What are the other properties of BaSO4?

Barium sulfate (BaSO₄) possesses several noteworthy properties, some of which are outlined below:

  1. Physical State: Barium sulfate is a white, crystalline solid at room temperature. It occurs naturally as the mineral "barite" and is commonly synthesized for various applications.

  2. Density: Barium sulfate has a relatively high density, typically around 4.5 grams per cubic centimeter (g/cm³). This density makes it useful for certain applications, such as in radiology as a contrast agent.

  3. Insolubility: As previously discussed, barium sulfate is highly insoluble in water and most common solvents. This property contributes to its use in medical imaging procedures (e.g., barium sulfate suspensions for X-ray examinations of the gastrointestinal tract) and as a filler in various materials.

  4. Chemical Inertness: Barium sulfate is chemically inert, meaning it does not readily react with other substances under normal conditions. This inertness is advantageous in applications where chemical stability is essential, such as in paints, coatings, and plastics.

  5. Non-Toxicity: Barium sulfate is considered non-toxic, which further supports its use in medical applications. When consumed in small quantities (e.g., in medical tests), it passes through the body without being absorbed or causing harm.

  6. Refractive Index: Barium sulfate has a relatively high refractive index, making it useful as a filler in products like paint and plastics to enhance opacity and brightness.

  7. Thermal Stability: Barium sulfate exhibits good thermal stability, retaining its physical and chemical properties at elevated temperatures. This characteristic makes it suitable for applications in industries where high temperatures are involved.

  8. Electrical Insulator: Due to its non-conductive nature, barium sulfate serves as an excellent electrical insulator. This property is valuable in applications where electrical isolation is necessary, such as in electronic devices and insulating materials.

  9. X-ray Absorption: Barium sulfate has high X-ray absorption properties, which is why it is used as a contrast agent in medical imaging procedures like barium X-rays. It allows for clear visualization of the gastrointestinal tract and certain anatomical structures.

  10. Photographic Uses: Barium sulfate was historically used in black-and-white photography as a white pigment in photographic paper and certain emulsions.

Overall, the unique combination of properties exhibited by barium sulfate makes it valuable in various industrial, medical, and commercial applications. Its insolubility, chemical inertness, and X-ray absorption properties, in particular, make it a versatile and sought-after material in different fields.


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