Question

Which of these ionic compounds will be more soluble in acid solution than in water: (a) \(\mathrm{BaSO}_{4}\) (b) \(\mathrm{PbCl}_{2},\) (c) \(\mathrm{Fe}(\mathrm{OH})_{3}\) (d) \(\mathrm{CaCO}_{3}\) ? Explain.

Short answer

C: \(\mathrm{Fe}(\mathrm{OH})_{3}\) and D: \(\mathrm{CaCO}_{3}\) are more soluble in acid solution than in water since their reactions with acid result in products that do not further disassociate into ions.

Step-by-step solution

Understanding the compounds' reactions with acid

Let's consider each compound's behavior in an acid solution: (a) \(\mathrm{BaSO}_{4}\) reacts with acid but it forms \(\mathrm{H}_{2}\mathrm{SO}_{4}\), which is a strong acid and disassociates completely into ions, thus not enhancing the solubility. (b) \(\mathrm{PbCl}_{2}\) also reacts with acid, but it forms \(\mathrm{HCl}\), another strong acid that disassociates completely into ions, so it doesn't help solubility.(c) \(\mathrm{Fe}(\mathrm{OH})_{3}\) reacts with acid to create \(\mathrm{H}_{2}\mathrm{O}\), which does not further ionize, meaning this can enhance the solubility.(d) \(\mathrm{CaCO}_{3}\) reacts with acid to form \(\mathrm{H}_{2}\mathrm{O}\) and \(\mathrm{CO}_{2}\), both of which do not further ionize, thus increasing solubility.

Conclusion: Which compounds are more soluble in acid

Therefore, based on these reactions, we can see that (c) \(\mathrm{Fe}(\mathrm{OH})_{3}\) and (d) \(\mathrm{CaCO}_{3}\) will be more soluble in an acid solution than in water. The other compounds do react with the acid, but they form strong acids, which disassociate completely, not helping solubility.

Key concepts

Ionic Compounds

Ionic compounds consist of positively charged cations and negatively charged anions held together by the strong electrostatic forces known as ionic bonds. These compounds have distinct properties, such as high melting points, and their structures are often crystalline in nature.

When dissolved in water, ionic compounds dissociate into their respective ions, a process fundamental to many chemical reactions. The degree and conditions under which an ionic compound dissolves is determined by factors such as temperature, the nature of the solvent, and presence of other substances, like acids, which may affect solubility.

Acid-Base Reactions

Acid-base reactions are a subset of chemical reactions that involves the transfer of protons (H+) between reactants. In water, acids tend to donate protons while bases accept them. These reactions are not only crucial in laboratory settings but also play a significant role in many biological and environmental processes.

For example, when certain ionic compounds are placed in an acid solution, the acid (proton donor) can react with the anions of the compound, potentially increasing the solubility of the compound if a weakly ionizing substance is formed.

Solubility Rules

Solubility rules are guidelines that help predict the solubility of different compounds in water. These rules indicate which types of ionic compounds typically dissolve in water (soluble) and which ones generally do not (insoluble).

However, the presence of an acid can alter the solubility. Compounds with anions that form weak acids are more soluble in an acidic solution than in pure water. This is because the acid reacts with the base formed by those anions, reducing their concentration and thus driving the dissolution of the compound further by Le Chatelier's principle.

Chemical Dissociation

Chemical dissociation refers to the separation of a substance into two or more simpler substances, or into its constituent ions or radicals, usually in a reversible manner. In the context of ionic compounds in solution, dissociation is the process where the compound breaks apart into its ions.

Strong acids or strong bases dissociate almost completely, meaning they produce a significant concentration of ions, whereas weak acids or bases do not dissociate completely, leaving fewer ions in solution. Understanding the extent of dissociation is key in predicting the behavior of substances in various environments, including their solubility in acidic solutions.