Skip to main content
Biochemistry
Biochemistry
6th Edition
ISBN: 9781305577206
Author: Reginald H. Garrett, Charles M. Grisham
Publisher: Cengage Learning
Not helpful? See similar books
Biochemistry
Biochemistry
Water: The Medium Of Life. 8P

(a) To calculate: The approximate fractional concentrations of H 3 PO 4 at pH values of 0,2,4,6,8,10, and 12. Concept Introduction: Phosphoric acid has three H+ dissociations. H 3 PO 4 ⇌ H + + H 2 PO 4 − pK a 1 = 2.15 H 2 PO 4 − ⇌ H + + HPO 4 2 − pK a 2 = 7.20 HPO 4 2 − ⇌ H + + PO 4 3 − pK a 3 = 12.4 The Henderson-Hasselbalch equation is as follows: p H = p K a + log [ A − ] [ H A ]

Question
Chapter 2, Problem 8P
Interpretation Introduction

(a)

To calculate:

The approximate fractional concentrations of H3PO4 at pH values of 0,2,4,6,8,10, and 12.

Concept Introduction:

Phosphoric acid has three H+ dissociations.

  H3PO4H++H2PO4     pKa1=2.15H2PO4H++HPO42     pKa2=7.20HPO42H++PO43        pKa3=12.4

The Henderson-Hasselbalch equation is as follows:

  pH=pKa+log[A][HA]

Expert Solution

Explanation of Solution

Rearranging the Henderson-Hasselbalch equation as follows:

  pH=pKa+log[ A ][HA][ A ][HA]=antilog(pHpKa)

At particular pH, [H2PO4-][H3PO4] = x, [HPO42-][H2PO4-] = y, [PO43-][HPO42-] = z

Fraction of any species at a particular pH is concentration of the species divided by the sum of the concentration of all species.

  fH3PO4=[H3PO4][H3PO4]+[H2PO4-]+[HPO42-]+[PO43-]

We can rewrite the above equation as a function of x, y, and z.

  fH3PO4=[ H 3 PO 4][ H 3 PO 4]+x[ H 3 PO 4]+xy[ H 3 PO 4]+xyz[ H 3 PO 4]fH3PO4=11+x+xy+xyz

We can manually calculate x, y, z and fractions of each species, but it is time consuming. Therefore, for efficiency we can calculate them using a spread sheet as follows:

    pH x y z
    0 0.00707946 6.3096E-08 3.9811E-13
    2 0.70794578 6.3096E-06 3.9811E-11
    4 70.7945784 0.00063096 3.9811E-09
    6 7079.45784 0.06309573 3.9811E-07
    8 707945.784 6.30957344 3.9811E-05
    10 70794578.4 630.957344 0.00398107
    12 7079457844 63095.7344 0.39810717

Thus,

    pH Fraction of H3PO4
    0 0.993
    2 0.585
    4 0.014
    6 0.000
    8 0.000
    10 0.000
    12 0.000
Interpretation Introduction

(b)

To calculate:

The approximate fractional concentrations of H2PO4- at pH values of 0,2,4,6,8,10, and 12 should be calculated

Introduction:

Phosphoric acid has three H+ dissociations.

  H3PO4H++H2PO4     pKa1=2.15H2PO4H++HPO42     pKa2=7.20HPO42H++PO43        pKa3=12.4

The Henderson-Hasselbalch equation is as follows:

  pH=pKa+log[A][HA]

Expert Solution

Explanation of Solution

Rearranging the Henderson-Hasselbalch equation as follows:

  pH=pKa+log[ A ][HA][ A ][HA]=antilog(pHpKa)

At particular pH, [H2PO4-][H3PO4] = x, [HPO42-][H2PO4-] = y, [PO43-][HPO42-] = z

Fraction of any species at a particular pH is concentration of the species divided by the sum of the concentration of all species.

  fH2PO4-=[H2PO4-][H3PO4]+[H2PO4-]+[HPO42-]+[PO43-]

We can rewrite the above equation as a function of x, y, and z.

  fH2 PO4=[ H 2 PO 4 ] [ H 2 PO 4 ]x+[ H 2 PO 4 ]+y[ H 2 PO 4 ]+yz[ H 2 PO 4 ]fH2 PO4=11x+1+y+yz

We can manually calculate x, y, z and fractions of each species, but it is time consuming. Therefore, for efficiency we can calculate them using a spread sheet as follows:

    pH x y z
    0 0.00707946 6.3096E-08 3.9811E-13
    2 0.70794578 6.3096E-06 3.9811E-11
    4 70.7945784 0.00063096 3.9811E-09
    6 7079.45784 0.06309573 3.9811E-07
    8 707945.784 6.30957344 3.9811E-05
    10 70794578.4 630.957344 0.00398107
    12 7079457844 63095.7344 0.39810717

Thus,

    pH Fraction of H2PO4-
    0 0.007
    2 0.415
    4 0.985
    6 0.941
    8 0.137
    10 0.002
    12 0.000
Interpretation Introduction

(c)

To calculate:

The approximate fractional concentrations of HPO42- at pH values of 0,2,4,6,8,10, and 12.

Introduction:

Phosphoric acid has three H+ dissociations.

  H3PO4H++H2PO4     pKa1=2.15H2PO4H++HPO42     pKa2=7.20HPO42H++PO43        pKa3=12.4

The Henderson-Hasselbalch equation is as follows:

  pH=pKa+log[A][HA]

Expert Solution

Explanation of Solution

Rearranging the Henderson-Hasselbalch equation as follows:

  pH=pKa+log[ A ][HA][ A ][HA]=antilog(pHpKa)

At particular pH, [H2PO4-][H3PO4] = x, [HPO42-][H2PO4-] = y, [PO43-][HPO42-] = z

Fraction of any species at a particular pH is concentration of the species divided by the sum of the concentration of all species.

  fHPO42-=[HPO42-][H3PO4]+[H2PO4-]+[HPO42-]+[PO43-]

We can rewrite the above equation as a function of x, y, and z.

  f HPO4 2=[ HPO 4 2] [ HPO 4 2 ] xy+ [ HPO 4 2 ]y+[ HPO 4 2]+z[ HPO 4 2]f HPO4 2=11 xy+1y+1+z

We can manually calculate x, y, z and fractions of each species, but it is time consuming. Therefore, for efficiency we can calculate them using a spread sheet as follows:

    pH x y z
    0 0.00707946 6.3096E-08 3.9811E-13
    2 0.70794578 6.3096E-06 3.9811E-11
    4 70.7945784 0.00063096 3.9811E-09
    6 7079.45784 0.06309573 3.9811E-07
    8 707945.784 6.30957344 3.9811E-05
    10 70794578.4 630.957344 0.00398107
    12 7079457844 63095.7344 0.39810717

Thus,

    pH Fraction of HPO42-
    0 0.000
    2 0.000
    4 0.001
    6 0.059
    8 0.863
    10 0.994
    12 0.715
Interpretation Introduction

(d)

To calculate:

The approximate fractional concentrations of PO43- at pH values of 0,2,4,6,8,10, and 12.

Concept Introduction:

Phosphoric acid has three H+ dissociations.

  H3PO4H++H2PO4     pKa1=2.15H2PO4H++HPO42     pKa2=7.20HPO42H++PO43        pKa3=12.4

The Henderson-Hasselbalch equation is as follows:

  pH=pKa+log[A][HA]

Expert Solution

Explanation of Solution

Rearranging the Henderson-Hasselbalch equation as follows:

  pH=pKa+log[ A ][HA][ A ][HA]=antilog(pHpKa)

At particular pH, [H2PO4-][H3PO4] = x, [HPO42-][H2PO4-] = y, [PO43-][HPO42-] = z

Fraction of any species at a particular pH is concentration of the species divided by the sum of the concentration of all species.

  fPO43-=[PO43-][H3PO4]+[H2PO4-]+[HPO42-]+[PO43-]

We can rewrite the above equation as a function of x, y, and z.

  f PO4 3=[ PO 4 3] [ PO 4 3 ] xyz+ [ PO 4 3 ] yz+ [ PO 4 3 ]z+[ PO 4 3]f PO4 3=11 xyz+1 yz+1z+1

We can manually calculate x, y, z and fractions of each species, but it is time consuming. Therefore, for efficiency we can calculate them using a spread sheet as follows:

    pH x y z
    0 0.00707946 6.3096E-08 3.9811E-13
    2 0.70794578 6.3096E-06 3.9811E-11
    4 70.7945784 0.00063096 3.9811E-09
    6 7079.45784 0.06309573 3.9811E-07
    8 707945.784 6.30957344 3.9811E-05
    10 70794578.4 630.957344 0.00398107
    12 7079457844 63095.7344 0.39810717

Thus,

    pH Fraction of PO43-
    0 0.000
    2 0.000
    4 0.000
    6 0.000
    8 0.000
    10 0.004
    12 0.285

Want to see more full solutions like this?

Subscribe now to access step-by-step solutions to millions of textbook problems written by subject matter experts!
Biochemistry
Biochemistry
6th Edition
ISBN: 9781305577206
Author: Reginald H. Garrett, Charles M. Grisham
Publisher: Cengage Learning
Not helpful? See similar books
Biochemistry
Biochemistry
Water: The Medium Of Life. 8P
Learn more about
Human Movement
marketing sidebar icon
Want to see more full solutions like this?
Subscribe now to access step-by-step solutions to millions of textbook problems written by subject matter experts.
Knowledge Booster
Biochemistry
Learn more about
Need a deep-dive on the concept behind this application? Look no further. Learn more about this topic, biochemistry and related others by exploring similar questions and additional content below.
Recommended textbooks for you
  • Biochemistry
    Biochemistry
    ISBN:9781305577206
    Author:Reginald H. Garrett, Charles M. Grisham
    Publisher:Cengage Learning
  • Biochemistry
    Biochemistry
    ISBN:9781305577206
    Author:Reginald H. Garrett, Charles M. Grisham
    Publisher:Cengage Learning