Chemistry: An Atoms-Focused Approach (Second Edition)
Chemistry: An Atoms-Focused Approach (Second Edition)
2nd Edition
ISBN: 9780393614053
Author: Thomas R. Gilbert, Rein V. Kirss, Stacey Lowery Bretz, Natalie Foster
Publisher: W. W. Norton & Company
Question
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Chapter 15, Problem 15.53QA
Interpretation Introduction

To find:

The value of Ka for lactic acid

Expert Solution & Answer
Check Mark

Answer to Problem 15.53QA

Solution:

Ka=8.91 ×10-4

Explanation of Solution

1) Concept:

We are asked to determine the Ka value for lactic acid from known initial concentration of the acid and given percent ionization. Lactic acid (CH3CHOHCOOH)  indicates that only one H atom per molecule is ionisable in aqueous solution.

The ionization reaction of butanoic acid can be written as

CH3CHOHCOOH aq+H2OlCH3CHOHCOO-aq+H3O+(aq)

And the equilibrium constant expression can be written as

Ka=CH3CHOHCOO-H3O+[CH3CHOHCOOH ]

2) Formulae:

i) Percent ionization=A-equilibriumHAinitial ×100

ii) Ka=CH3CHOHCOO-H3O+[CH3CHOHCOOH]

3) Given:

i) Initial concentration of butanoic acid is 1.00M

ii) Percent ionization of the acid is 2.94%

4) Calculations:

From the given percent dissociation, we can find the CH3CHOHCOO-equilibrium using the percent dissociation formula as

Percent ionization=CH3CHOHCOO-equilibriumCH3CHOHCOOHinitial ×100

2.94%=CH3CHOHCOO-equilibrium1.00 M ×100

0.0294=CH3CHOHCOO-equilibrium1.00 M

C3H7COO-equilibrium=0.0294 ×1.00 M=0.0294 M

The equilibrium concentration of CH3CHOHCOO- is calculated as 0.0294M.

We can set up the RICE table to solve this problem.

Reaction CH3CHOHCOOH aq+H2OlCH3CHOHCOO-aq+H3O+aq CH3CHOHCOOH (M) CH3CHOHCOO-(M) H3O+ (M)
Initial (I) 1.00 0.00 0.00
Change (C) -x +x +x
Equilibrium (E) 1.00-x x x

At equilibrium, H3O+=CH3CHOHCOO-=x=2.94×10-2M

The equilibrium concentration for the acid is

CH3CHOHCOOHequilibrium=CH3CHOHCOOHinitial-H3O+equilibrium

CH3CHOHCOOHequilibrium=1.00-2.94×10-2M= 0.9706M

Inserting the equilibrium values for all the species in the Ka expression, we get

Ka=CH3CHOHCOO-H3O+[CH3CHOHCOOH]

Ka=2.94×10-22.94×10-20.9706 =8.905 ×10-4

Thus, the acid dissociation constant value for lactic acid is 8.91 ×10-4

Conclusion:

Ka value is calculated from the initial concentration and percent ionization of lactic acid.

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Chapter 15 Solutions

Chemistry: An Atoms-Focused Approach (Second Edition)

Ch. 15 - Prob. 15.11QACh. 15 - Prob. 15.12QACh. 15 - Prob. 15.13QACh. 15 - Prob. 15.14QACh. 15 - Prob. 15.15QACh. 15 - Prob. 15.16QACh. 15 - Prob. 15.17QACh. 15 - Prob. 15.18QACh. 15 - Prob. 15.19QACh. 15 - Prob. 15.20QACh. 15 - Prob. 15.21QACh. 15 - Prob. 15.22QACh. 15 - Prob. 15.23QACh. 15 - Prob. 15.24QACh. 15 - Prob. 15.25QACh. 15 - Prob. 15.26QACh. 15 - Prob. 15.27QACh. 15 - Prob. 15.28QACh. 15 - Prob. 15.29QACh. 15 - Prob. 15.30QACh. 15 - Prob. 15.31QACh. 15 - Prob. 15.32QACh. 15 - Prob. 15.33QACh. 15 - Prob. 15.34QACh. 15 - Prob. 15.35QACh. 15 - Prob. 15.36QACh. 15 - Prob. 15.37QACh. 15 - Prob. 15.38QACh. 15 - Prob. 15.39QACh. 15 - Prob. 15.40QACh. 15 - Prob. 15.41QACh. 15 - Prob. 15.42QACh. 15 - Prob. 15.43QACh. 15 - Prob. 15.44QACh. 15 - Prob. 15.45QACh. 15 - Prob. 15.46QACh. 15 - Prob. 15.47QACh. 15 - Prob. 15.48QACh. 15 - Prob. 15.49QACh. 15 - Prob. 15.50QACh. 15 - Prob. 15.51QACh. 15 - Prob. 15.52QACh. 15 - Prob. 15.53QACh. 15 - Prob. 15.54QACh. 15 - Prob. 15.55QACh. 15 - Prob. 15.56QACh. 15 - Prob. 15.57QACh. 15 - Prob. 15.58QACh. 15 - Prob. 15.59QACh. 15 - Prob. 15.60QACh. 15 - Prob. 15.61QACh. 15 - Prob. 15.62QACh. 15 - Prob. 15.63QACh. 15 - Prob. 15.64QACh. 15 - Prob. 15.65QACh. 15 - Prob. 15.66QACh. 15 - Prob. 15.67QACh. 15 - Prob. 15.68QACh. 15 - Prob. 15.69QACh. 15 - Prob. 15.70QACh. 15 - Prob. 15.71QACh. 15 - Prob. 15.72QACh. 15 - Prob. 15.73QACh. 15 - Prob. 15.74QACh. 15 - Prob. 15.75QACh. 15 - Prob. 15.76QACh. 15 - Prob. 15.77QACh. 15 - Prob. 15.78QACh. 15 - Prob. 15.79QACh. 15 - Prob. 15.80QACh. 15 - Prob. 15.81QACh. 15 - Prob. 15.82QACh. 15 - Prob. 15.83QACh. 15 - Prob. 15.84QACh. 15 - Prob. 15.85QACh. 15 - Prob. 15.86QACh. 15 - Prob. 15.87QACh. 15 - Prob. 15.88QACh. 15 - Prob. 15.89QACh. 15 - Prob. 15.90QACh. 15 - Prob. 15.91QACh. 15 - Prob. 15.92QACh. 15 - Prob. 15.93QACh. 15 - Prob. 15.94QACh. 15 - Prob. 15.95QACh. 15 - Prob. 15.96QACh. 15 - Prob. 15.97QACh. 15 - Prob. 15.98QACh. 15 - Prob. 15.99QACh. 15 - Prob. 15.100QACh. 15 - Prob. 15.101QACh. 15 - Prob. 15.102QACh. 15 - Prob. 15.103QACh. 15 - Prob. 15.104QACh. 15 - Prob. 15.105QACh. 15 - Prob. 15.106QACh. 15 - Prob. 15.107QACh. 15 - Prob. 15.108QACh. 15 - Prob. 15.109QACh. 15 - Prob. 15.110QA
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