Determine if each salt will form a solution that is acidic, basic, or pH-neutral. a. Al(NO3)3 b. C2H5NH3NO3 c. K2CO3 d. RbI e. NH4ClO

Understanding the nature of salt solutions begins by recognizing that salts can cause the resulting solution to be acidic, basic, or neutral. Acidic salts are those which come from the neutralization of a strong acid and a weak base. For instance, in step 1 and step 2 of the exercise, Al(NO3)3 and C2H5NH3NO3 are examples of acidic salts. The reason lies in the fact that their cations (Al3+ and C2H5NH3+, respectively) are capable of reacting with water, a process known as hydrolysis, to release H+ ions into the solution. This increases the concentration of H+ ions, lowering the pH and hence creating an acidic medium.

Conversely, basic salts result from the neutralization of a strong base and a weak acid. Take K2CO3 from step 3 for example. The carbonate ion (CO3^2-) is the result of neutralizing H2CO3 with a strong base. This ion will hydrolyze to produce OH- ions, which elevate the OH- concentration and raise the pH, thereby making the solution basic. It's critical to recognize these ions' behavior in water to predict the pH of their solutions effectively.

Hydrolysis of salts refers to the reaction of salt ions with water to form an acidic or basic solution. This pivotal concept helps us decipher why certain solutions exhibit certain pH values. Hydrolysis occurs when an ion reacts with water, accepting or donating a hydrogen ion (H+).

As detailed in the exercise's solutions, for Al(NO3)3 in step 1, the Al3+ ion reacts with water, which results in the production of H+ ions. The NO3- ion, however, does not react with water since it is the conjugate base of a strong acid and is, therefore, considered aweak base incapable of significantly changing the pH of the solution. Meanwhile, for NH4ClO in step 5, the NH4+ ion is a weak acid and also hydrolyzes to release H+ ions, while ClO- remains relatively inactive in terms of hydrolysis. The tendency of a salt ion to hydrolyze is linked to the strengths of its parent acid or base—a weak acid or base would produce ions more likely to undergo hydrolysis.

The concept of conjugate acid-base pairs is central to understanding the pH of salt solutions. Each pair consists of two species that transform into each other by the gain or loss of a proton (H+ ion). When an acid donates an H+ ion, it becomes its conjugate base, while a base accepting an H+ ion becomes its conjugate acid.

In the context of the given exercise, the cation C2H5NH3+ in step 2 is the conjugate acid of a weak base (ethanamine), indicating that it can give up an H+ ion to the solution. Similarly, the CO3^2- anion in K2CO3 (step 3) is the conjugate base of a weak acid (carbonic acid), thus capable of attracting an H+ ion to form OH- ions making the solution basic. Since none of the ions from RbI (step 4) tend to gain or lose H+ ions readily, they don't form a conjugate acid-base pair that significantly affects the pH, rendering the solution pH-neutral. Recognizing these pairs and their relative strengths is crucial in predicting the behavior of salts in solution.