   Chapter 15, Problem 54E

Chapter
Section
Textbook Problem

# Calculate the number of moles of HCl(g) that must be added to 1.0 L of 1.0 M NaC2H3O2 to produce a solution buffered at each pH.a. pH = pKab. pH = 4.20c. pH = 5.00

(a)

Interpretation Introduction

Interpretation:

The concentration and volume of NaC2H3O2 is given. The quantity (moles) of HCl 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.

To determine the number of moles of NaC2H3O2

Explanation

Explanation

Given

Concentration of NaC2H3O2 is 1.0M .

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)(1.0M)=1.0mol_

To determine the pKa value

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

NaC2H3O2+HClC2H4O2+NaCl

The number of moles of C2H4O2 left after the reaction is 1.0x .

The value of Ka of C2H4O2 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 HCl 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 HCl is added. The reaction is,

NaC2H3O2+HClC2H4O2+NaCl

The number of moles of C2H4O2 left after the reaction is 1

(b)

Interpretation Introduction

Interpretation:

The concentration and volume of NaC2H3O2 is given. The quantity (moles) of HCl 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.

To determine the quantity (moles) of HCl that must be added to produce buffer solution when pH=4.20 .

(c)

Interpretation Introduction

Interpretation:

The concentration and volume of NaC2H3O2 is given. The quantity (moles) of HCl 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.

To determine the quantity (moles) of HCl that must be added to produce buffer solution when pH=5.00 .

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