   # Arsenic acid (H 3 AsO 4 ) is a triprotic acid with K a 1 = 5.5 × 10 −3 , K a 2 = 1.7 × 10 −7 , and K a 3 = 5.1 × 10 −12 . Calculate [H + ], [OH − ], [H 3 AsO 4 ], [H 2 AsO 4 − ], [HAsO 4 2− ], and [AsO 4 3− ] in a 0.20- M arsenic acid solution. ### 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 108E
Textbook Problem
17 views

## Arsenic acid (H3AsO4) is a triprotic acid with K a 1 = 5.5 × 10−3, K a 2 = 1.7 × 10−7, and K a 3 = 5.1 × 10−12. Calculate [H+], [OH−], [H3AsO4], [H2AsO4−], [HAsO42−], and [AsO43−] in a 0.20-M arsenic acid solution.

Interpretation Introduction

Interpretation: The value of [H+],[OH],[H2AsO4],[HAsO42] and [AsO43] for a 0.20M solution of arsenic acid is to be calculated.

Concept introduction: Arsenic acid is a weak acid; therefore, it dissociates up to a very small extent and slowly in an aqueous solution.

To determine: The value of [H+],[OH],[H3AsO4],[HAsO42] and [AsO43] for a 0.20M solution of arsenic acid.

### Explanation of Solution

Explanation

Given

The standard value of Ka1 for arsenic acid is 5.5×103.

The standard value of Ka2 for arsenic acid is 1.7×107.

The standard value of Ka3 for arsenic acid is 5.1×1012.

The dissociated amount of [H+] and [H2AsO4] from the arsenic acid (H3AsO4) is assumed to be x. The concentration of [H+] and [H2AsO4] is calculated by using the ICE (Initial Change Equilibrium) table.

H3AsO4H++H2AsO4Initial(M):0.2000Change(M):xxxEquilibrium(M):0.20xxx

The value of acid dissociation equilibrium constant Ka is calculated by the formula,

Ka=[Concentrationofproducts][Concentrationofreactants]

Thus, Ka for the above stated reaction is,

Ka1=[H+][H2AsO42][H3AsO4]

Substitute the values of Ka1, concentration of reactants and products from the ICE table in the above expression.

5.5×103=[x][x][0.20x]x2+5.5×103x1.1×103=0x=0.0305M_

Hence, the values of [H+] and [H2AsO4] at equilibrium is 0.0305M_.

The dissociated amount of [H+] and [HAsO42] from H2AsO41 is assumed to be y. The concentration of [H+] and [HAsO42] is calculated by using the ICE (Initial Change Equilibrium) table.

H2AsO4H++HAsO42Initial(M):0.030500Change(M):yyyEquilibrium(M):0.0305yyy

The value of acid dissociation equilibrium constant Ka is calculated by the formula.

Ka=[Concentrationofproducts][Concentrationofreactants]

Thus, Ka for the above stated reaction is,

Ka2=[H+][HAsO42][H2AsO41]

Substitute the values of Ka2, concentration of reactants and products from the ICE table in the above expression.

1.7×107=[x][x][0.0305x]x2+1.7×107x5.18×109=0x=7.18×10-5M_

Hence, the values of [H+] and [HAsO42] at equilibrium is 7

### Still sussing out bartleby?

Check out a sample textbook solution.

See a sample solution

#### The Solution to Your Study Problems

Bartleby provides explanations to thousands of textbook problems written by our experts, many with advanced degrees!

Get Started

Find more solutions based on key concepts
A person who exercises moderately for longer than 20 minutes begins to a. use less glucose and more fat for fue...

Nutrition: Concepts and Controversies - Standalone book (MindTap Course List)

Give the IUPAC name for each of the following: a. b c.

Chemistry for Today: General, Organic, and Biochemistry

What is an extremophile?

Oceanography: An Invitation To Marine Science, Loose-leaf Versin

A particle with electric charge is fired into a region of space where the electric field is zero. It moves in a...

Physics for Scientists and Engineers, Technology Update (No access codes included) 