Chapter 16, Problem 54PS

### 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

# Phenol (C 6 H 5 OH) commonly called carbolic acid is a weak organic acid C 6 H 5 OH (aq) + H 2 O ( l )  ⇌ C 6 H 5 O − (aq) + H 3 O + (aq)    K a = 1 .3×10 − 10 If you dissolve 0.195 g of the acid in enough water to make 125ml of solution. What is the equilibrium hydronium ion concentration? What is the pH of the solution?

Interpretation Introduction

Interpretation:

The equilibrium of hydronium ion concentration and 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

Volume of solution = 125ml

Dissolved mass of phenol =.0.195g

Molecular mass of phenol = 94g/mol

MolarityÂ ofÂ phenolÂ =Â MolesÂ ofÂ phenolÂ (mol)VolumeÂ ofÂ theÂ solution

(0.195g94g/mol)(1125mlÂ Ã—Â 1000mL1L)Â Â =Â 0.0166M

The phenol reacts with water. The equilibrium reaction is as follows.

C6H5OHÂ (aq)Â +H2OÂ (l)Â â‡ŒC6H5O-Â (aq)Â +Â H3O+(aq)

The equilibrium expression,

Ka(C6H5OH)Â =Â [C6H5O-][H3O+][C6H5OH]

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 C6H5OHÂ (aq)Â +H2OÂ (l)Â Â â‡ŒC6H5O-Â (aq)Â +Â H3O+(aq)IÂ Â Â Â Â Â Â 0.0166Â 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 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 xÂ Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â +xEÂ Â Â Â Â (0.0166Â -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 xÂ Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â x

Ka of phenol is 1

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