Question

Using solubility guidelines, predict whether each of the following compounds is soluble or insoluble in water: (a) \(\mathrm{NiCl}_{2}\), (b) \(\mathrm{Ag}_{2} \mathrm{~S}\), (c) \(\mathrm{Cs}_{3} \mathrm{PO}_{4}\) (d) \(\mathrm{SrCO}_{3}\) (e) \(\mathrm{PbSO}_{4}\).

Short answer

Based on the solubility guidelines, the following compounds have the respective solubilities in water: (a) \(NiCl_2\) is soluble, (b) \(Ag_2S\) is insoluble, (c) \(Cs_3PO_4\) is soluble, (d) \(SrCO_3\) is insoluble, and (e) \(PbSO_4\) is insoluble.

Step-by-step solution

(a) Solubility of NiCl₂

According to rule 2, most chloride salts are soluble in water except for those containing silver, lead, and mercury(I). Nickel(II) chloride, NiCl₂, does not contain any of these exceptions, so it is soluble in water.

(b) Solubility of Ag₂S

According to rule 5, most sulfide salts are insoluble in water except for those containing ammonium, alkali metals, and calcium. Silver(I) sulfide, Ag₂S, contains silver, which does not fall under any of these exceptions, so it is insoluble in water.

(c) Solubility of Cs₃PO₄

According to rule 1, most phosphate salts are insoluble in water, except for those containing ammonium and alkali metals. Cesium is an alkali metal, so cesium phosphate, Cs₃PO₄, is soluble in water.

(d) Solubility of SrCO₃

According to rule 4, most carbonate salts are insoluble in water, except for those containing ammonium and alkali metals. Strontium carbonate, SrCO₃, contains strontium, which does not fall under any of these exceptions, so it is insoluble in water.

(e) Solubility of PbSO₄

According to rule 3, most sulfate salts are soluble in water, except for those containing calcium, strontium, barium, and lead. Lead(II) sulfate, PbSO₄, contains lead, which falls under one of these exceptions, so it is insoluble in water.

Key concepts

Solubility of Ionic Compounds

Understanding the solubility of ionic compounds is crucial in various fields, from chemical synthesis to environmental science. Solubility refers to the ability of a substance to dissolve in a solvent. For ionic compounds, which are made of positively and negatively charged ions, water is often the solvent of interest because of its polarity.

The process of dissolution involves the ions of the solute separating and interacting with the water molecules. These interactions are governed by the lattice energy of the ionic compound, which is the energy required to separate the ions, and the hydration energy, the energy released when water molecules surround the ions.

Key Factors Influencing Solubility

• Ion Charge: Compounds with higher charges tend to have higher lattice energies, which makes them less soluble.
• Ion Size: Smaller ions have stronger interactions with water molecules and are usually more soluble.
• Temperature: Raising the temperature can increase solubility by providing more energy to overcome lattice energy.

Understanding these principles aids in predicting whether an ionic compound will be soluble in water.

Predicting Compound Solubility

Predicting the solubility of compounds requires familiarity with various solubility rules. These rules are based on empirical observations and can be quite reliable for anticipating if a compound will dissolve in water. Students often use a chart or a set of guidelines that summarize these rules.

To predict solubility effectively, it's beneficial to memorize some general trends:

General Solubility Trends

• Most alkali metal salts and ammonium salts are soluble.
• Nitrates, acetates, and most perchlorates are soluble.
• Halides are generally soluble, with exceptions for silver, lead, and mercury I.
• Most carbonates, sulfides, oxides, and phosphates are insoluble, except when paired with alkali metals or ammonium.

However, understanding the why behind these rules can greatly enhance the predictive power. This involves considering the interplay of factors such as lattice energy and hydration energy, as well as the thermodynamics of the dissolution process.

Solubility Guidelines in Water

The solubility guidelines in water serve as a useful reference for determining whether a compound is likely soluble or insoluble. These guidelines culminate from years of experimental observations and are summarized into an easy-to-consult chart or list.

For instance, salts containing nitrate (NO₃⁻) ions are almost always soluble, while most salts containing carbonate (CO₃²⁻) ions are not, unless they're paired with an alkali metal ion or ammonium (NH₄⁺).

Here's how to apply these guidelines to textbook problems:

Solubility Application

• Identify the ions that make up the compound.
• Consult the solubility guidelines to determine the general solubility of these ion pairings.
• Consider any exceptions that might apply to the compound in question.
• Remember that solubility can also be affected by concentration and temperature.

Using these guidelines, students can systematically approach problems and develop a grounded understanding of chemical solubility.