   # Table 13-4 lists the stepwise K a values for some polyprotic acids. What is the difference between a monoprotic acid, a diprotic acid, and a triprotic acid? Most polyprotic acids are weak acids; the major exception is H 2 SO 4 . To solve for the pH of a solution of H 2 SO 4 , you must generally solve a strong acid problem as well as a weak acid problem. Explain. Write out the reactions that refer to K a 1 and K a 2 for H 2 SO 4 . For H 3 PO 4 , K a 1 = 7.5 × 10 −3 , K a 2 = 6.2 × 10 −8 , and K a 3 = 4.8 × 10 −13 . Write out the reactions that refer to the K a 1 , K a 2 and K a 3 equilibrium constants. What are the three acids in a solution of H 3 PO 4 ? Which acid is strongest? What are the three conjugate bases in a solution of H 3 PO 4 ? Which conjugate base is strongest? Summarize the strategy for calculating the pH of a polyprotic acid in water. ### 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 13, Problem 7RQ
Textbook Problem
3 views

## Table 13-4 lists the stepwise Ka values for some polyprotic acids. What is the difference between a monoprotic acid, a diprotic acid, and a triprotic acid? Most polyprotic acids are weak acids; the major exception is H2SO4. To solve for the pH of a solution of H2SO4, you must generally solve a strong acid problem as well as a weak acid problem. Explain. Write out the reactions that refer to K a 1 and K a 2 for H2SO4.For H3PO4, K a 1 = 7.5 × 10−3, K a 2 = 6.2 × 10−8, and K a 3 = 4.8 × 10−13. Write out the reactions that refer to the K a 1 , K a 2 and K a 3 equilibrium constants. What are the three acids in a solution of H3PO4? Which acid is strongest? What are the three conjugate bases in a solution of H3PO4? Which conjugate base is strongest? Summarize the strategy for calculating the pH of a polyprotic acid in water.

Interpretation Introduction

Interpretation: The difference between monoprotic acid, diprotic acid, triprotic acid, pH calculation of H2SO4 , reactions referring to Ka1,Ka2 and Ka3 equilibrium constants , pH calculation of polyprotic acid

Concept introduction: Acids are distinguished based upon their number of protons. H2SO4 is a diprotic acid. Each successive step of equilibrium of proton donation is written in stepwise-equilibrium constant form. For polyprotic acid we consider stepwise-equilibrium constant.

### Explanation of Solution

Explanation

To determine: The difference between monoprotic acid, diprotic acid, triprotic acid, pH calculation of H2SO4 , reactions referring to  equilibrium constants Ka1,Ka2 and Ka3 , pH calculation of polyprotic acid

Acids having only 1 proton attached to them are called monoprotic acids while acids having 2 and 3 protons attached to them are called diprotic and triprotic acids respectively.

The compound H2SO4 is an exception in polyprotic acids as initially it furnishes H+ and HSO4 ions as a strong acid but in the second step HSO4 ion behaves as a weak acid giving H+ and SO42 with difficulty and an equilibrium is established between the reactants and products. The reactions that take place are,

H2SO4H++HSO4HSO4H++SO2

Now using an ICE table the stepwise-equilibrium constant values are calculated.

The compound H3PO4 is a triprotic acid furnishing 3 protons in 3 successive steps.

Proton donating reactions of H3PO4 along with stepwise-equilibrium constant expression is stated as follows.

The initial dissociation reaction is,

H3PO4H++H2PO4

The acid dissociation constant is calculated by the formula as,

Ka=[concentrationofproducts][concentrationofreactants] (1)

Therefore, for the stated reaction, the equilibrium constant expression is,

Ka1=[H+][H2PO4][H3PO4]=7

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