Question

Specify which of these salts will undergo hydrol\(\begin{array}{llll}\text { ysis: } \mathrm{KF}, & \mathrm{NaNO}_{3}, & \mathrm{NH}_{4} \mathrm{NO}_{2}, & \mathrm{MgSO}_{4}, & \mathrm{KCN},\end{array}\) \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{COONa}, \mathrm{RbI}, \mathrm{Na}_{2} \mathrm{CO}_{3}, \mathrm{CaCl}_{2}, \mathrm{HCOOK}\).

Short answer

The salts that will undergo hydrolysis are KF, NH4NO2, MgSO4, KCN, Na2CO3, and HCOOK.

Step-by-step solution

Determine the ions

The first step to determine whether these salts will undergo hydrolysis or not is to look at their ions. A salt is made up of a cation (positive ion) and an anion (negative ion). The salts have the following cations and anions: KF has K+ and F-, NaNO3 has Na+ and NO3-, NH4NO2 has NH4+ and NO2-, MgSO4 has Mg2+ and SO42-, KCN has K+ and CN-, C6H5COONa has C6H5COO- and Na+, RbI has Rb+ and I-, Na2CO3 has Na+ and CO32-, CaCl2 has Ca2+ and 2Cl-, and HCOOK has HCOO- and K+.

Determine the ability to undergo hydrolysis

Hydrolysis occurs when ions from the salt react with water. Salts of neutral pH won't undergo hydrolysis, meaning if the anion and cation both come from strong bases and strong acids respectively, the salt will not undergo hydrolysis. Salts with cations of weak bases or anions from weak acids will undergo hydrolysis. Through this approach, the salts that would undergo hydrolysis would be: KF, NH4NO2, MgSO4, KCN, Na2CO3, and HCOOK.

Summarize Findings

The salts that would undergo hydrolysis are: KF (due to F-, which comes from weak acid HF), NH4NO2 (due to NH4+, which comes from weak base NH3), MgSO4 (due to Mg2+, which comes from weak base Mg(OH)2), KCN (due to CN-, which comes from weak acid HCN), Na2CO3 (due to CO32-, which comes from weak acid H2CO3), and HCOOK (due to HCOO-, which comes from weak acid HCOOH).

Key concepts

Ions in Salts

Salts are composed of positive ions, known as cations, and negative ions, known as anions. These combinations result from the reaction between acids and bases. When studying a salt, you can break it down into its constituent ions to understand its properties better. For example, in the salt KF, K is the cation \(\text{K}^+\) and F is the anion \(\text{F}^-\). When dissolved in water, these ions become the active participants in chemical interactions.
Other examples include \(\text{NaNO}_3 \) which contains \(\text{Na}^+\) and \(\text{NO}_3^-\), and \(\text{MgSO}_4\) containing \(\text{Mg}^{2+}\) and \(\text{SO}_4^{2-}\). The combination of ions determines whether a salt will undergo certain reactions, such as hydrolysis. Understanding each ion's origin, whether from strong or weak acids/bases, is crucial in predicting these interactions.

Weak Acids and Bases

The acidity or basicity of the salts is determined by the source of their ions. A significant concept is that ions originating from weak acids and bases will have a tendency to undergo hydrolysis when dissolved in water. Hydrolysis is the chemical breakdown of a compound due to reaction with water.
For example, \(\text{CN}^-\), the anion found in \(\text{KCN}\), is derived from the weak acid hydrogen cyanide (HCN). Similarly, \(\text{NH}_4^+\), found in \(\text{NH}_4\text{NO}_2\), comes from the weak base ammonia (NH3). When these ions come from a weak acid or base, they will react with water, affecting the pH of the solution and demonstrating the hydrolysis response.

Chemical Reactions in Water

Chemical reactions in water can alter the properties of dissolved substances like salts. When salts dissolve, their ions dissociate and can participate in hydrolysis. Hydrolysis of salts is crucial as it influences the pH levels of the solution.
In water, ions like \(\text{F}^-\) from \(\text{KF}\) and \(\text{CN}^-\) from \(\text{KCN}\) will react to form their weak acids (HF and HCN, respectively). This reaction with water typically occurs when ions are from weak acids and bases, shifting the pH slightly acidic or basic. This is why recognizing the parent acid or base of each ion is important, as it helps predict the chemical behavior of the solution.