Chapter 16, Problem 53PS

### Chemistry & Chemical Reactivity

10th Edition
John C. Kotz + 3 others
ISBN: 9781337399074

Chapter
Section

### Chemistry & Chemical Reactivity

10th Edition
John C. Kotz + 3 others
ISBN: 9781337399074
Textbook Problem

# What are the equilibrium concentration of H 3 O + , CN‒ and HCN in a 0.025 M solution of HCN? What is the pH of the solution?

Interpretation Introduction

Interpretation:

The equilibrium concentration of H3O+,CN- and HCN in a 0.025 M solution of HCN and also pH of the solution has to be calculated.

Concept introduction:

Equilibrium constants:

The equilibrium constant is used to quantitative measurement of the strength of the acid and bases in the water.

Ka is acid constant for equilibrium reactions.

HA + H2OH3O++ A-Ka[H3O+][A-][HA]

Kb is base constant for equilibrium reaction.

BOH + H2OB++ OH-Ka[B+][OH-][BOH]

Explanation

The equation for the reaction of a HCN with water and its equilibrium constant expression are

HCN(aq)Â +Â H2O(l)Â â‡ŒCN-(aq)Â +Â H3O+(aq)Ka(HCN)=Â [CN-][H3O+][HCN]

Enter the ICE table the concentrations before equilibrium is established, the change that occurs as the reaction proceeds to equilibrium and the concentrations when equilibrium has been achieved.

Â Â Â Â Â Â Â HCN(aq)Â Â Â Â Â +Â Â H2O(l)Â â‡ŒCN-Â +Â H3O+IÂ Â Â Â Â Â Â 0.025Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â --Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â --Â Â Â Â Â Â Â Â Â Â --CÂ Â Â Â Â Â Â Â Â Â -xÂ Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â --Â Â Â Â Â Â Â Â Â Â Â Â Â Â +Â xÂ Â Â Â Â Â Â +Â xEÂ Â Â Â (0.025Â -Â x)Â Â Â Â Â Â Â Â Â Â Â --Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â xÂ Â Â Â Â Â Â Â Â Â Â x

The Ka of the Hydrogen cyanide is 4.0Ã—10-10

Ka(HCN)Â =Â [CN-][H3O+][HCN]Â =Â 4.0Ã—10-10

4

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