   # For the reaction of hydrazine (N 2 H 4 ) in water, H 2 NNH 2 ( a q ) + H 2 O ( l ) ⇌ H 2 NNH 3 + ( a q ) + OH − ( a q ) K b is 3.0 × 10 −6 . Calculate the concentrations of all species and the pH of a 2.0- M solution of hydrazine 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 96E
Textbook Problem
449 views

## For the reaction of hydrazine (N2H4) in water, H 2 NNH 2 ( a q ) + H 2 O ( l ) ⇌ H 2 NNH 3 + ( a q ) + OH − ( a q ) Kb is 3.0 × 10−6. Calculate the concentrations of all species and the pH of a 2.0-M solution of hydrazine in water.

Interpretation Introduction

Interpretation: The concentration of all the species present in the given 2.0M solution of hydrazine in water and the pH value of the solution is to be calculated.

Concept introduction: The pH of a solution is defined as a figure that expresses the acidity of the alkalinity of a given solution.

The pOH of a solution is calculated by the formula, pOH=log[OH]

The sum, pH+pOH=14

At equilibrium, the equilibrium constant expression is expressed by the formula,

Kb=ConcentrationofproductsConcentrationofreactants

To determine: The concentration of all the species present in the given 2.0M solution of hydrazine in water and the pH value of the solution.

### Explanation of Solution

Explanation

The major species present in the given solution of hydrazine (H2NNH2) in water are H2NNH3+ , OH and H2O .

H2NNH2 is a weak base.

In the presence of water, the reaction that takes place is,’

H2NNH2(aq)+H2O(l)H2NNH3+(aq)+OH(aq)

The major species present in the given solution of H2NNH3+ , OH and H2O .

The equilibrium constant expression for the given reaction is, Kb=[H2NNH3+][OH][H2NNH2]

At equilibrium, the equilibrium constant expression is expressed by the formula,

Kb=ConcentrationofproductsConcentrationofreactants

Where,

• Kb is the base ionization constant.

The equilibrium constant expression for the given reaction is,

Kb=[H2NNH3+][OH][H2NNH2] (1)

The [OH] is 2.45×10-3M_ .

The change in concentration of H2NNH2 is assumed to be x .

The liquid components do not affect the value of the rate constant.

The ICE table for the stated reaction is,

H2NNH2(aq)H2NNH3+(aq)+OH(aq)Inititialconcentration2.000Changex+x+xEquilibriumconcentration2.0xxx

The equilibrium concentration of [H2NNH2] is (2.0x)M .

The equilibrium concentration of [H2NNH3+] is xM .

The equilibrium concentration of [OH] is xM .

The Kb value is given to be 3.0×106 .

Substitute the value of Kb , [H2NNH2] , [H2NNH3+] and [OH] in equation (1).

3.0×106=[x][x][2

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