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11 Nov 2019

In a solution, when the concentrations of a weak acid and its conjugate base are equal, ________.

1.
the -log of the [H⁺] and the -log of the K_a are equal

2.
the buffering capacity is significantly decreased

3.
the system is not at equilibrium

4.
All of the above are true.

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A good buffer generally contains relatively equal concentrations of weak acid and conjugate base. If you wanted to buffer a solution at pH = 4.00 or pH = 10.00, how would you decide which weak acid-conjugate base or weak base-conjugate acid pair to use? The second characteristic of a good buffer is good buffering capacity. What is the capacity of a buffer? How do the following buffers differ in capacity? How do they differ in pH?

0.01 M acetic acid/0.01 M sodium acetate

0.1 M acetic acid/0.1 M sodium acetate

1.0 M acetic acid/1.0 M sodium acetate

magentamammoth658

A good buffer generally contains relatively equal concentrations of weak acid and conjugate base. If you wanted to buffer a solution at pH = 4.00 or pH = 10.00, how would you decide which weak acid–conjugate base or weak base–conjugate acid pair to use? The second characteristic of a good buffer is good buffering capacity. What is the capacity of a buffer? How do the following buffers differ in capacity? How do they differ in pH?

0.01 M acetic acid/0.01 M sodium acetate

0.1 M acetic acid/0.1 M sodium acetate

1.0 M acetic acid/1.0 M sodium acetate

pucehamster19

Experiment 18: Buffers Purpose In this experiment you will prepare several buffers and investigate their properties. Discussion A solution of a weak acid and one of its salts, in approximately equal concentrations, resists changes in pH when acid or base is added to it. (Note: The pH of a solution is a measure of the concentration of free H3Ot ion; it does not indicate concentration of combined acid such as HA.) The same is true for a solution of a weak base and one of its salts. A solution with this property is called a buffer (see illustration next page). Bufter systems are extremely important in many chemical and biological systems. For example, your blood contains a buffer system utilizing carbonic acid and bicarbonate ion. The important equilibrium in an acidic buffer is HA (aq) H20 ) A (a)0 () acid conjugate base in which the concentrations of acid and conjugate base are approximately equal. If a small amount of free acid (H30) is added to this solution, it reacts with the conjugate base A (reaction 1 in reverse). The equilibrium constant for this reaction is very large, so the reaction proceeds to near completion, absorbing the added acid. Similarly, added base (OH-) reacts with the acid HA as shown below: 2. HA (aq) + OH-(aq) ATaq) + H2O (1) This reaction also proceeds to completion, effectively absorbing any added base. Since the H30 and OH- concentrations are kept constant, the solution thus resists pH changes when an acid or base is added to it. A similar argument can be made for a basic buffer The actual pH of a buffer can be determined from the value of the Ka and the concentrations of the acid and conjugate base obtained from an initial-change- equilibrium table. However, a shortcut for buffers is available, and is shown below. We begin by writing and rearranging the equilibrium constant expression for the acid dissociation. If the -log of both sides of equation (3) is taken, a relationship involving pH is then obtained. H30IA] HA] 3. HA HAI -loglH30'1- -log Ka A- 141

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In a solution, when the concentrations of a weak acid and its conjugate base are equal, ________.

1.
the -log of the [H⁺] and the -log of the K_a are equal

2.
the buffering capacity is significantly decreased

3.
the system is not at equilibrium

4.
All of the above are true.

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Principles of Chemistry Molecular Approach

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1.		the -log of the [H⁺] and the -log of the K_a are equal
2.		the buffering capacity is significantly decreased
3.		the system is not at equilibrium
4.		All of the above are true.

In a solution, when the concentrations of a weak acid and its conjugate base are equal, ________. 1. the -log of the [H+] and the -log of the Ka are equal 2. the buffering capacity is significantly decreased 3. the system is not at equilibrium 4. All of the above are true.

Unlock all answers

Related textbook solutions

Basic Chemistry

Principles of Chemistry Molecular Approach

Principles of Chemistry Molecular Approach

Chemistry: Structure and Properties

Chemistry: A Molecular Approach

Chemistry: A Molecular Approach

Principles of Chemistry: A Molecular Approach

Chemistry: The Central Science

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Weekly leaderboard

In a solution, when the concentrations of a weak acid and its conjugate base are equal, ________.

1.
the -log of the [H⁺] and the -log of the K_a are equal

2.
the buffering capacity is significantly decreased

3.
the system is not at equilibrium

4.
All of the above are true.