Predict whether aqueous solutions of the following compounds are acidic, basic, or neutral: (a) NH4Br (b) FeCl3 (c) KClO4 (d) NaHC2O4.

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Identify the ions produced when each compound dissociates in water. For example, NH4Br dissociates into NH4^+ and Br^- ions.

Determine the nature of each ion. NH4^+ is the conjugate acid of NH3, which is a weak base, so NH4^+ is a weak acid. Br^- is the conjugate base of HBr, a strong acid, so Br^- is neutral.

For FeCl3, Fe^3+ is a small, highly charged metal ion that can hydrolyze water to produce H^+ ions, making the solution acidic. Cl^- is the conjugate base of HCl, a strong acid, so Cl^- is neutral.

For KClO4, K^+ is the cation of a strong base (KOH) and is neutral. ClO4^- is the conjugate base of a strong acid (HClO4) and is also neutral, so the solution is neutral.

For NaHC2O4, Na^+ is neutral as it is the cation of a strong base (NaOH). HC2O4^- can act as a weak acid, as it can donate a proton to form C2O4^2-, making the solution slightly acidic.

Key Concepts

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

Acid-Base Theory

Acid-base theory explains how substances can donate or accept protons (H+ ions). According to the Brønsted-Lowry theory, acids are proton donors, while bases are proton acceptors. Understanding this concept is crucial for predicting the behavior of compounds in solution, as it helps determine whether a solution will be acidic, basic, or neutral based on the ions produced.

Salt Hydrolysis

Salt hydrolysis occurs when an ionic compound dissolves in water and its constituent ions interact with water molecules, potentially altering the pH of the solution. Some ions can react with water to produce H+ or OH- ions, leading to acidic or basic solutions. Recognizing which ions are present in the salts given in the question is essential for predicting the resulting solution's acidity or basicity.

Common Ion Effect

The common ion effect describes how the addition of an ion common to a weak acid or base can suppress its ionization. This principle is important when considering the behavior of salts in solution, as the presence of certain ions can shift equilibrium positions, affecting the acidity or basicity of the solution. Understanding this effect helps in analyzing how the ions from the compounds influence the overall pH.

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Common Ion Effect

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Pyridinium bromide 1C5H5NHBr2 is a strong electrolyte that dissociates completely into C5H5NH+ and Br-. An aqueous solution of pyridinium bromide has a pH of 2.95. (b) Using Appendix D, calculate the Ka for pyridinium bromide.

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Pyridinium bromide 1C5H5NHBr2 is a strong electrolyte that dissociates completely into C5H5NH+ and Br-. An aqueous solution of pyridinium bromide has a pH of 2.95. (c) A solution of pyridinium bromide has a pH of 2.95. What is the concentration of the pyridinium cation at equilibrium, in units of molarity?

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