Question

Characterize the following compounds as soluble or insoluble in water: (a) \(\mathrm{Ca}_{3}\left(\mathrm{PO}_{4}\right)_{2},\) (b) \(\mathrm{Mn}(\mathrm{OH})_{2}\), (c) \(\mathrm{AgClO}_{3},\) (d) \(\mathrm{K}_{2} \mathrm{~S}\).

Short answer

(a) Insoluble, (b) Insoluble, (c) Soluble, (d) Soluble.

Step-by-step solution

Determine Solubility of \(\text{Ca}_3(\text{PO}_4)_2\)

Calcium phosphate, \(\text{Ca}_3(\text{PO}_4)_2\), is generally insoluble in water. Most phosphate salts are insoluble, with the exception of those involving Group 1 elements and ammonium.

Determine Solubility of \(\text{Mn(OH)}_2\)

Manganese(II) hydroxide, \(\text{Mn(OH)}_2\), is typically insoluble in water. Hydroxides are usually insoluble except for those of Group 1 elements and some members of Group 2, like Ba(OH)₂.

Determine Solubility of \(\text{AgClO}_3\)

Silver chlorate, \(\text{AgClO}_3\), is soluble in water. Most chlorates are soluble regardless of their cations.

Determine Solubility of \(\text{K}_2\text{S}\)

Potassium sulfide, \(\text{K}_2\text{S}\), is soluble in water. Compounds with Group 1 elements like potassium are generally soluble.

Key concepts

Insoluble Compounds

Insoluble compounds are those that do not dissolve readily in water. Take calcium phosphate, \(\mathrm{Ca}_{3}\left(\mathrm{PO}_{4}\right)_{2}\), for example. This compound is a common insoluble phosphate. Most phosphate compounds do not dissolve in water, except when they are paired with Group 1 elements like sodium and potassium, or ammonium ions.
Reasons for Insolubility:

• Strong ionic bonds within the compound that water molecules cannot break.
• Formation of a lattice structure that is stable and does not allow water to penetrate easily.

Because of these strong interactions, only a small amount, if any, of the compound dissolves in water. Understanding solubility rules can help identify similar insoluble compounds. This is important in fields like chemistry and environmental science.

Soluble Compounds

Soluble compounds dissolve easily in water, breaking up into ions. Potassium sulfide, \(\mathrm{K}_{2}\mathrm{~S}\), is one such example. Potassium, a Group 1 element, typically forms soluble compounds. When these substances dissolve, they dissociate into ions, which can move freely in solution.
Factors Influencing Solubility:

• The nature of the ion pair (like potassium and sulfide) that facilitate dissolving.
• The hydration energy which is released when ions interact with water molecules.

Chlorates, including silver chlorate \(\mathrm{AgClO}_{3}\), are also usually soluble. Their solubility is due to the chlorate ions forming weak bonds that are easy for water to break. This ease of division allows compounds to mix effectively in aqueous solutions.

Water Solubility

Water solubility refers to a substance's ability to dissolve in water to form a homogeneous solution. It is a vital concept in chemistry for determining how compounds behave in aqueous environments. The solubility can be affected by several factors such as temperature, pressure, and the presence of other chemicals.
Key Points:

• Temperature: Generally, increasing temperature increases solubility for solids in liquids.
• Pressure: Mainly affects gases, where higher pressures usually increase solubility.
• Interactions: Solvent-solute interactions are critical for determining how well a compound can dissolve.

Understanding whether a compound is soluble or not helps in various applications, from industrial processes to biological systems.

Compound Characterization

Compound characterization involves determining a substance's physical and chemical properties. This can include solubility, which helps define how a compound interacts with water. Manganese(II) hydroxide, \(\mathrm{Mn(OH)}_{2}\), is usually classified as insoluble. Such hydroxides do not dissolve significantly unless bound to more soluble elements like those in Group 1 of the periodic table.
Techniques for Characterization:

• Solubility testing: Determines how much of a compound dissolves in water.
• Analytical methods: Techniques like spectroscopy or chromatography identify compound structure.
• Chemical reactivity: Observes how a substance reacts with other chemicals, aiding in understanding compound behavior.

Characterizing compounds is essential for chemists and industries to utilize the right substances for desired reactions and processes.