Question

Using solubility guidelines, predict whether each of the following compounds is soluble or insoluble in water: (a) \(\mathrm{Hg}_{2} \mathrm{SO}_{4}\) (b) \(\mathrm{NH}_{4} \mathrm{OH}\), (c) \(\mathrm{Ni}\left(\mathrm{CH}_{3} \mathrm{COO}\right)_{2}\) (d) \(\mathrm{AgNO}_{3}\), (e) FeCO \(_{3}\)

Short answer

Using solubility guidelines, we can predict the following compounds solubility in water: (a) \(\mathrm{Hg}_{2} \mathrm{SO}_{4}\) is insoluble. (b) \(\mathrm{NH}_{4} \mathrm{OH}\) is soluble. (c) \(\mathrm{Ni}\left(\mathrm{CH}_{3} \mathrm{COO}\right)_{2}\) is soluble. (d) \(\mathrm{AgNO}_{3}\) is soluble. (e) FeCO \(_{3}\) is insoluble.

Step-by-step solution

Solubility Guideline Rules

Some of the solubility guideline rules are as follows: 1. All salts containing alkali metals, ammonium (\(\mathrm{NH}_{4}^{+}\)), and nitrates (\(\mathrm{NO}_{3}^{-}\)) are soluble. 2. All salts containing acetates (\(\mathrm{CH}_{3}\mathrm{COO}^{-}\)) and sulfates (\(\mathrm{SO}_{4}^{2-}\)) are soluble, with a few exceptions (e.g., silver, lead, and mercury(I)). 3. All salts containing the halides (e.g., \(\mathrm{Cl}^{-}\), \(\mathrm{Br}^{-}\), \(\mathrm{I}^{-}\)) are soluble, with a few exceptions (e.g., silver, lead, and mercury(I)). 4. All salts containing carbonates (\(\mathrm{CO}_{3}^{2-}\)), phosphates (\(\mathrm{PO}_{4}^{3-}\)), and sulfides (\(\mathrm{S}^{2-}\)) are insoluble, with a few exceptions for the alkali metals and ammonium. Now we will apply the guidelines to each compound in the exercise: (a) \(\mathrm{Hg}_{2} \mathrm{SO}_{4}\)

Solubility of \(\mathrm{Hg}_{2} \mathrm{SO}_{4}\)

Although most sulfates are soluble, there are a few exceptions, including mercury(I) sulfate. In this case, we have \(\mathrm{Hg}_{2} \mathrm{SO}_{4}\) which is mercury(I) sulfate. Therefore, this compound is insoluble in water. (b) \(\mathrm{NH}_{4} \mathrm{OH}\)

Solubility of \(\mathrm{NH}_{4} \mathrm{OH}\)

The compound contains the ammonium ion \(\mathrm{NH}_{4}^{+}\). According to the solubility guideline rules, all salts containing ammonium ions are soluble. Therefore, \(\mathrm{NH}_{4} \mathrm{OH}\) is soluble in water. (c) \(\mathrm{Ni}\left(\mathrm{CH}_{3} \mathrm{COO}\right)_{2}\)

Solubility of \(\mathrm{Ni}\left(\mathrm{CH}_{3} \mathrm{COO}\right)_{2}\)

This compound contains the acetate ion \(\mathrm{CH}_{3}\mathrm{COO}^{-}\). All salts containing acetates are soluble in water, as stated in the solubility guidelines. Therefore, \(\mathrm{Ni}\left(\mathrm{CH}_{3} \mathrm{COO}\right)_{2}\) is soluble in water. (d) \(\mathrm{AgNO}_{3}\)

Solubility of \(\mathrm{AgNO}_{3}\)

This compound contains the nitrate ion \(\mathrm{NO}_{3}^{-}\). According to the solubility guidelines, all salts containing nitrates are soluble in water. Therefore, \(\mathrm{AgNO}_{3}\) is soluble in water. (e) FeCO \(_{3}\)

Solubility of FeCO \(_{3}\)

This compound contains a carbonate ion \(\mathrm{CO}_{3}^{2-}\). The solubility guidelines state that all salts containing carbonates are insoluble in water, with a few exceptions for alkali metals and ammonium. Since iron (Fe) does not belong to either of these exceptions, FeCO \(_{3}\) is insoluble in water.

Key concepts

Solubility Guidelines

Solubility guidelines are essential tools in chemistry to predict whether a compound will dissolve in water. They are based on experimental observations and help identify the general solubility patterns of ionic compounds in aqueous solutions.

These guidelines work by classifying compounds according to the ions they contain. Here are a few key rules to remember:

• Salts containing alkali metals (like sodium and potassium) and the ammonium ion ( NH_4^+ ) are always soluble.
• Sulfates ( SO_4^{2-} ) and acetates ( CH_3COO^- ) are generally soluble, with exceptions for certain heavy metals like lead, barium, and mercury(I).
• Nitrate ( NO_3^- ) salts are uniformly soluble without exceptions.
• Carbonates ( CO_3^{2-} ), phosphates ( PO_4^{3-} ), and sulfides ( S^{2-} ) tend to be insoluble, unless they're paired with alkali metals or ammonium.

These rules allow chemists to quickly deduce the solubility of a compound and predict how it behaves in a chemical reaction.

Ionic Compounds

Ionic compounds are a class of compounds formed from charged particles known as ions. These ions can either be positive (cations) or negative (anions). Ionic compounds in solid form create a lattice structure, maintaining a balance between the positive and negative charges.

When ionic compounds dissolve in water, they dissociate into their individual ions. For example, when sodium chloride ( NaCl ) dissolves in water, it separates into sodium ions ( Na^+ ) and chloride ions ( Cl^- ). This dissociation is what allows ionic compounds to conduct electricity in aqueous solutions.

• The strength of an ionic bond and the solubility of the compound are related. Compounds with strong bonds may be more difficult to dissolve.
• The arrangement of ions in the lattice can also affect solubility. For example, compounds with larger ions are often more soluble.

Understanding these factors helps in predicting and explaining solubility based on the nature of the compound.

Aqueous Solutions

Aqueous solutions are solutions where water is the solvent—a crucial aspect of many chemical reactions. In these solutions, the dissolved substance, or solute, interacts with water molecules, often changing its properties.

Water is commonly used as a solvent because it's abundant and a powerful solvent due to its polar nature. Its polarity allows water molecules to surround and stabilize ions and polar molecules, facilitating their dispersion throughout the solution.

• In an aqueous solution, the solute particles are surrounded by a layer of solvent molecules. This process is known as solvation or hydration when water is the solvent.
• Aqueous solutions can conduct electricity if the solute produces ions when dissolved. These are called electrolytic solutions.

Recognizing the behavior of compounds in aqueous solutions is essential for understanding how they will react and interact in various chemical scenarios.

Chemical Reactions

Chemical reactions in aqueous solutions often involve the formation or dissolution of ionic compounds. These reactions may include precipitation, neutralization, and redox reactions.

When an ionic compound dissolves in water, a chemical reaction may occur, producing new compounds or ions. For example, when two different solutions are mixed, their ions can form an insoluble compound that precipitates out of solution. This is known as a precipitation reaction.

• A neutralization reaction occurs when an acid and a base react to form water and a salt, typically resulting in an aqueous solution.
• Redox reactions in aqueous solutions transfer electrons between substances, thus changing their oxidation states.

Understanding the types of chemical reactions that can occur in aqueous solutions helps in predicting the products of reactions and their various applications in chemistry.