An unknown salt is either KBr, NH4Cl, KCN, or K2CO3. If a 0.100 M solution of the salt is neutral, what is the identity of the salt?

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Identify the possible ions from each salt: KBr (K+ and Br-), NH4Cl (NH4+ and Cl-), KCN (K+ and CN-), K2CO3 (2K+ and CO3^2-).

Consider the nature of each ion in water: K+ is neutral, Br- is neutral, NH4+ is a weak acid, Cl- is neutral, CN- is a weak base, and CO3^2- is a weak base.

Determine the effect of each ion on the pH of the solution. Salts containing neutral ions (K+ and Cl-) will not affect the pH, making the solution neutral. Salts with a weak acid or weak base will make the solution either slightly acidic or slightly basic.

Compare the pH effect of each salt with the information given that the solution is neutral. This means the salt must be composed of ions that do not alter the pH significantly.

Conclude that the salt which forms a neutral solution and matches the given concentration is KBr, as it contains ions (K+ and Br-) that do not affect the pH of the solution.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Acid-Base Neutrality

A neutral solution has a pH of around 7, indicating that the concentrations of hydrogen ions (H+) and hydroxide ions (OH-) are equal. In the context of salts, a neutral solution typically arises from the reaction of a strong acid with a strong base, resulting in no excess H+ or OH- ions. Understanding the acid-base properties of the ions in the salt is crucial for determining whether the solution will be neutral.

Salt Hydrolysis

Salt hydrolysis refers to the reaction of a salt with water, which can lead to the formation of acidic or basic solutions. When a salt dissolves, its constituent ions can interact with water, potentially altering the pH. For example, salts derived from strong acids and strong bases do not hydrolyze significantly, while those from weak acids or bases can create acidic or basic solutions, affecting neutrality.

Identifying Ions in Salts

To identify the unknown salt, it is essential to analyze the ions it contains. KBr consists of K+ and Br-, NH4Cl contains NH4+ and Cl-, KCN has K+ and CN-, and K2CO3 includes K+ and CO3^2-. By evaluating the properties of these ions, particularly their acid-base behavior, one can determine which salt would produce a neutral solution when dissolved in water.