   # What quantity (moles) of NaOH must be added to 1.0 L of 2.0 M HC 2 H 3 O 2 to produce a solution buffered at each pH? a. pH = p K a b. pH = 4.00 c. pH = 5.00 ### Chemistry: An Atoms First Approach

2nd Edition
Steven S. Zumdahl + 1 other
Publisher: Cengage Learning
ISBN: 9781305079243

#### Solutions

Chapter
Section ### Chemistry: An Atoms First Approach

2nd Edition
Steven S. Zumdahl + 1 other
Publisher: Cengage Learning
ISBN: 9781305079243
Chapter 14, Problem 53E
Textbook Problem
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## What quantity (moles) of NaOH must be added to 1.0 L of 2.0 M HC2H3O2 to produce a solution buffered at each pH?a. pH = pKab. pH = 4.00c. pH = 5.00

(a)

Interpretation Introduction

Interpretation:

The concentration and volume of HC2H3O2 is given. The quantity (moles) of NaOH that must be added to produce buffer solution is to be calculated from the given conditions.

Concept introduction:

A solution that contains mixture of a weak acid and its conjugate base is known as buffer solution. The pH value is the measure of H+ ions.

### Explanation of Solution

Explanation

To determine the number of moles of HC2H3O2

Given

Concentration of HC2H3O2 is 2.0M .

Volume of solution is 1.0L .

The number of moles of a compound in a solution is calculated using the formula,

Molesofcompound=Concentrationofcompound×Volumeofsolution

Substitute the values of concentration and volume of solution in the above equation.

Molesofcompound=Concentrationofcompound×Volumeofsolution=(1.0L)(2.0M)=2.0moles_

To determine pKa

It is assumed that x moles of NaOH is added. The reaction is,

HC2H3O2+NaOHNaC2H3O2+H2O

The number of moles of HC2H3O2 left after the reaction is 2.0x .

The value of Ka of HC2H3O2 is 1.8×105 .

The formula of pKa is,

pKa=logKa

Where,

• Ka is acid equilibrium constant.

Substitute the value of Ka in the above equation.

pKa=logKa=log(1.8×105)=4.74_

To find the quantity (moles) of NaOH that must be added to produce buffer solution when pH=pKa

As the volume of solution is 1.0L , the concentration of compound is equal to number of moles.

It is assumed that x moles of NaOH is added and the number of moles of HC2H3O2 left after the reaction is 2.0x .

Formula

The pH is calculated using the Henderson-Hassel Bach equation,

pH=pKa+log[C2H3O2][HC2H3O2]

Where,

• pH is the measure of H+ ions

(b)

Interpretation Introduction

Interpretation:

The concentration and volume of HC2H3O2 is given. The quantity (moles) of NaOH that must be added to produce buffer solution is to be calculated from the given conditions.

Concept introduction:

A solution that contains mixture of a weak acid and its conjugate base is known as buffer solution. The pH value is the measure of H+ ions.

(c)

Interpretation Introduction

Interpretation:

The concentration and volume of HC2H3O2 is given. The quantity (moles) of NaOH that must be added to produce buffer solution is to be calculated from the given conditions.

Concept introduction:

A solution that contains mixture of a weak acid and its conjugate base is known as buffer solution. The pH value is the measure of H+ ions.

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