Question

Which salt can furnish \(\mathrm{H}^{+}\) in its aqueous solution? (a) \(\mathrm{NaH}_{2} \mathrm{PO}_{2}\) (b) \(\mathrm{Na}_{2} \mathrm{HPO}_{3}\) (c) \(\mathrm{Na}_{2}^{\circ} \mathrm{HPO}_{4}\) (d) All of these

Short answer

All of the given salts (a) \(\mathrm{NaH}_{2} \mathrm{PO}_{2}\), (b) \(\mathrm{Na}_{2} \mathrm{HPO}_{3}\), and (c) \(\mathrm{Na}_{2}^{\text{o}} \mathrm{HPO}_{4}\) can furnish \(\mathrm{H}^{+}\) ions in their aqueous solutions, so the correct answer is (d) All of these.

Step-by-step solution

Understanding the Problem

To determine which salt can furnish \(\mathrm{H}^{+}\) ions in its aqueous solution, we need to analyze the salts given and determine whether they contain any acidic hydrogen atoms that can be released as \(\mathrm{H}^{+}\) ions in solution.

Analyzing Salt (a) - \(\mathrm{NaH}_{2} \mathrm{PO}_{2}\)

Salt (a) \(\mathrm{NaH}_{2} \mathrm{PO}_{2}\) has two acidic hydrogen atoms attached to the phosphorus atom. In an aqueous solution, it can release one or both hydrogen atoms as \(\mathrm{H}^{+}\) ions.

Analyzing Salt (b) - \(\mathrm{Na}_{2} \mathrm{HPO}_{3}\)

Salt (b) \(\mathrm{Na}_{2} \mathrm{HPO}_{3}\) has one acidic hydrogen atom attached to the phosphorus atom. In an aqueous solution, it can release its hydrogen atom as a \(\mathrm{H}^{+}\) ion.

Analyzing Salt (c) - \(\mathrm{Na}_{2}^{\text{o}} \mathrm{HPO}_{4}\)

Salt (c) \(\mathrm{Na}_{2}^{\text{o}} \mathrm{HPO}_{4}\), which is also known as \(\mathrm{Na}_{2} \mathrm{HPO}_{4}\), has one acidic hydrogen atom attached to the phosphorus atom. In an aqueous solution, it can also release its hydrogen atom as a \(\mathrm{H}^{+}\) ion.

Conclusion

Since all options (a), (b), and (c) can release \(\mathrm{H}^{+}\) ions in solution, the correct answer is (d) All of these.

Key concepts

Aqueous Solution of Salts

When salts dissolve in water, they form an aqueous solution. This is a crucial concept for understanding how salts behave chemically. An aqueous solution is simply a solution in which the solvent is water. Salts are naturally composed of cations (positively charged ions) and anions (negatively charged ions). Upon dissolving, these ions separate and disperse throughout the solution.

Different salts can have various effects on the solution's pH level. For instance, if a salt releases H ions when it dissolves in water, the solution becomes acidic. Conversely, if a salt releases OH ions, the solution becomes basic. Salts that do not significantly affect the pH of the water, such as table salt (NaCl), are considered neutral.

Role of Water in Dissolving Salts

The polarity of water molecules allows them to surround and interact with the ions in salts. This interaction between water molecules and ions is what pulls the salt apart into its respective ions, thus creating an aqueous solution. Salts with acidic hydrogen atoms, like those in the exercise, can release H ions because the water molecules can destabilize the bond between the hydrogen atoms and the rest of the salt molecule, leading to the formation of hydrogen ions (H).

Hydrogen Ion Release

Understanding hydrogen ion release in aqueous solutions of salts is pivotal in acid-base chemistry. When acidic hydrogen atoms are present in a salt, they can be released as hydrogen ions (H) once the salt is dissolved in water. The ability of a salt to release H ions is linked to the strength of the bond between the hydrogen atom and the rest of the molecule.

Weakly bound hydrogen atoms, often found in the presence of electronegative elements or within certain molecular structures, are more likely to be ionized in water. This ionization process is governed by the principles of acid dissociation. An acid is a substance that can release H ions, thereby increasing the concentration of hydrogen ions in a solution.

Factors Influencing Hydrogen Ion Release

Several factors can affect the release of hydrogen ions from salts in water. These factors include the salt's structure, the presence of electronegative atoms near the acidic hydrogen, and the pH of the solution. For instance, the salts in the provided exercise, NaHPO and NaHPO, among others, contain acidic hydrogen atoms that can be released due to the instability of the H bond in an aqueous environment.

Acid-Base Chemistry in Physical Chemistry

Acid-base chemistry is a foundational aspect of physical chemistry and it focuses on the reactions and properties related to acids and bases. This field of chemistry primarily deals with the transfer of protons (H) between chemical species. Brønsted-Lowry theory defines acids as proton donors and bases as proton acceptors, which is significant in understanding the behavior of salts in water.

For a salt to act as an acid by releasing H ions, it must have an acidic proton. Not all protons in a salt molecule are acidic; it is typically those that are likely to be donated to water molecules or other bases. The concept of 'acidic hydrogen atoms in salts' refers to such hydrogens that can be donated, leading to the generation of hydronium ions (H) in solution.

pH and Acid-Base Equilibria

The pH of a solution is a measure of its acidity or basicity (alkalinity), which is determined by the concentration of hydrogen ions present. Acidic solutions have a higher concentration of H ions and thus a lower pH. The process of salts releasing hydrogen ions in water and hence affecting the pH is an example of an acid-base reaction. Equilibrium in acid-base reactions is crucial for understanding the extent to which a salt will affect the pH of a solution. Salts like those given in the exercise demonstrate this by their potential to release H ions and form corresponding conjugate bases in the solution.