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Chapter 15: Problem 91

Write the equilibrium equation and the equilibrium constant expression for an ammonia-ammonium ion buffer solution.

Short Answer

Expert verified
The equilibrium equation for an ammonia-ammonium ion buffer solution is \( NH3 (aq) + H2O (l) \leftrightarrow NH4+ (aq) + OH- (aq) \) and the equilibrium constant expression (Kb) is \( Kb = [NH4+][OH-] / [NH3] \)

Step by step solution

01

Understanding Buffer Solution

A buffer solution is an aqueous solution consisting of a mixture of a weak acid and its conjugate base or a weak base and its conjugate acid. It has the ability to maintain a constant pH even when small amounts of acid or base are added. For ammonia-ammonium ion buffer system, ammonia (NH3) serves as the weak base and ammonium ion (NH4+) serves as its conjugate acid.
02

Writing the Equilibrium Equation

The equilibrium within the buffer solution occurs when ammonia (the weak base) reacts with water, acting as acid, to form ammonium ions (the conjugate acid) and hydroxide ions. Hence, the equilibrium equation can be written as: \[ NH3 (aq) + H2O (l) \leftrightarrow NH4+ (aq) + OH- (aq) \] This equation reflects the balance between the reactants (NH3 and H2O) and the products (NH4+ and OH-).
03

Formulation of the Equilibrium Constant Expression

The equilibrium constant expression (Kb) for this reaction can be written as the ratio of the concentration of the products to the concentration of the reactants, with each concentration raised to the power of its stoichiometric coefficient. However, the concentration of water remains constant and is therefore not included in the expression. Thus, the equilibrium constant expression becomes: \[ Kb = [NH4+][OH-] / [NH3] \] This represents the basicity constant for ammonia.

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Most popular questions from this chapter

Why is a buret, rather than a graduated cylinder, used in titrations?

Calculate the concentration of the \(\mathrm{H}_{3} \mathrm{O}^{+}\) and \(\mathrm{OH}^{-}\) ions in an aqueous solution of pH \(5.0 .\)

A solution of a weak acid has a pH of \(4.7 .\) What is the hydronium ion concentration?

A small volume of indicator solution is usually added to the titration flask right before the titration. As a result, the sample is diluted slightly. Does this matter? Why or why not?

What is a base according to Arrhenius? according to Bronsted and Lowry?
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