Chapter 17, Problem 17PS

### Chemistry & Chemical Reactivity

10th Edition
John C. Kotz + 3 others
ISBN: 9781337399074

Chapter
Section

### Chemistry & Chemical Reactivity

10th Edition
John C. Kotz + 3 others
ISBN: 9781337399074
Textbook Problem

# Which of the following combinations would be the best to buffer the pH of a solution at approximately 9? (a) HCl and NaCl (b) NH3 and NH4C1 (c) CH3CO2H and NaCH3CO2

(a)

Interpretation Introduction

Interpretation:

A buffer solution is to be prepared with pH value approximately 9. Which of the following pair is suitable, HCl+ NaCl has to be found.

Concept introduction:

The Henderson-Hasselbalch equation relates pH of a buffer with pKa of acid, concentration of conjugate base and concentration of acid. The expression is written as,

pH=pKa+log[conjugatebase][acid] (1)

This equation shows that pH of buffer solution is controlled by two major factors. First, Strength of the acid can be expressed on terms of pKa and second, the relative concentration of acid and its conjugate base at equilibrium. It can be seen from equation (1) that pH of the buffer solution is comparable to pKa values. So this equation can be used to establish a relation between pH and pKa value of acid.

Explanation

The hydrochloric acid,HCl is a strong acid. It will undergo complete ionization in aqueous solution and give H3O+ and Clâˆ’. There is also Clâˆ’ ions areÂ  present in the mixture due to the ionization of NaCl

(b)

Interpretation Introduction

Interpretation:

A buffer solution is to be prepared with pH value approximately 9. Which of the following pair is suitable, NH3+ NH4Cl has to be found.

Concept introduction:

The Henderson-Hasselbalch equation relates pH of a buffer with pKa of acid, concentration of conjugate base and concentration of acid. The expression is written as,

pH=pKa+log[conjugatebase][acid] (1)

This equation shows that pH of buffer solution is controlled by two major factors. First, Strength of the acid can be expressed on terms of pKa and second, the relative concentration of acid and its conjugate base at equilibrium. It can be seen from equation (1) that pH of the buffer solution is comparable to pKa values. So this equation can be used to establish a relation between pH and pKa value of acid.

(c)

Interpretation Introduction

Interpretation:

A buffer solution is to be prepared with pH value approximately 9. Which of the following pair is suitable, CH3COOH+ CH3COONa has to be found.

Concept introduction:

The Henderson-Hasselbalch equation relates pH of a buffer with pKa of acid, concentration of conjugate base and concentration of acid. The expression is written as,

pH=pKa+log[conjugatebase][acid] (1)

This equation shows that pH of buffer solution is controlled by two major factors. First, Strength of the acid can be expressed on terms of pKa and second, the relative concentration of acid and its conjugate base at equilibrium. It can be seen from equation (1) that pH of the buffer solution is comparable to pKa values. So this equation can be used to establish a relation between pH and pKa value of acid.

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