   Chapter 16, Problem 72E

Chapter
Section
Textbook Problem

# Solutions of sodium thiosulfate are used to dissolve unexposed AgBr (Ksp = 5.0 × 10−13) in the developing process for black-and-white film. What mass of AgBr can dissolve in 1.00 L of 0.500 M Na2S2O3? Ag+ reacts with S2O32− to form a complex ion: Ag + ( a q )   +   2 S 2 O 3 2 − ( a q )   ⇌   A g ( S 2 O 3 ) 2 3 − ( a q )   K   =   2.9   ×   10 13

Interpretation Introduction

Interpretation: The mass of AgBr that can dissolve in 1.0L of 0.500M Na2S2O3 is to be calculated.

Concept introduction: Concept introduction: Solubility is defined as the maximum amount of solute that can dissolve at a certain amount of solvent at certain temperature. The solubility product, Ksp is the equilibrium constant that is applied when salt partially dissolve in a solvent. The solubility product of dissociation of AxBy is calculated by the formula,

Ksp=[A]x[B]y

Explanation

Explanation

To determine: The mass of AgBr that can dissolve in 1.0L of 0.500M Na2S2O3 .

The concentration of AgBr is 3.625mol/L_ .

Given

The volume of Na2S2O3 is 1.0L .

The molarity of Na2S2O3 is 0.500M .

AgBr is soluble in sodium thiosulfate.

The reactions that occur are,

AgBrAg++BrKsp(AgI)=5.0×1013Ag++2S2O32Ag(S2O3)23K=2.9×1013

Add the two equations. The final reaction is

AgBr+2S2O32Ag(S2O3)23+Br

The overall equilibrium constant for the reaction is calculated by the formula,

Ke=KspK

Where,

• Ksp is the solubility product of AgI .
• K is the overall formation constant.

Substitute the value of Ksp and K in the above expression.

Ke=(5.0×1013)(2.9×1013)=14.5

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

Ke=ConcentrationofproductsConcentrationofreactants

Where,

• Ke is the equilibrium constant.

The equilibrium constant expression for the given reaction is,

Ke=[Ag(S2O3)23][Br][AgBr][S2O32]2

The ICE table is formed.

InitialChangeEquilibrium AgBr+2S2O32Ag(S2O3)23+Br00

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