   Chapter 16, Problem 11PS

Chapter
Section
Textbook Problem

What is the pH of a 0.0075 M solution of HCl? What is the hydroxide ion concentration of the solution?

Interpretation Introduction

Interpretation:

For a given concentration of Hydrochloric acid (HCl) solution,pH and the concentration of hydroxide ion in the solution has to be calculated.

Concept introduction:

A strong acid completely dissociates into its constituent ions in aqueous solution, as a result, the concentration of its ion is same as the initial concentration of that strong acid.

For example, strong acid dissociates as follows in water,

HA(aq)+H2O(l)H3O+(aq)+A(aq)

[H3O+]=[A]=[HA]

The pH of a solution is basically the measure of the molar concentration of the H+ or H3O+ ion in the solution. More the concentration of H+ or H3O+ ion in the solution, lesser will be the pH value and more acidic will be the solution.

The expression for pH is given as,

pH=log[H3O+]

The concentration of OH ions is calculated by using the ionic product of water.

Kw=[H3O+][OH]

The value of Kw is 1.0×1014.

If pH<7 then, the solution is acidic in nature.

If pH >7 then, the solution is basic in nature.

If pH=7 then, the solution is neutral in nature.

Explanation

The value of pH for Hydrochloric acid (HCl) solution and the concentration of hydroxide ion in the solution is calculated below.

Given

The initial concentration of HCl solution is 0.0075 M.

HCl is a strong acid and it dissociates as follows in water,

HCl(aq)+H2O(l)H3O+(aq)+Cl(aq)

The ICE table is as follows,

EquilibriumHCl(aq)+H2O(l)H3O+(aq)+Cl(aq)Initial(M)0.007500Change(M)+0.0075+0.0075Equilibrium(M)0.00750.0075

From the table,

[H3O+]=0.0075 M

The expression for pH is given as,

pH=log[H3O+]

Substitute 0

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