   Chapter 16, Problem 37QAP ### Introductory Chemistry: A Foundati...

9th Edition
Steven S. Zumdahl + 1 other
ISBN: 9781337399425

#### Solutions

Chapter
Section ### Introductory Chemistry: A Foundati...

9th Edition
Steven S. Zumdahl + 1 other
ISBN: 9781337399425
Textbook Problem
4 views

# . Why do scientists tend to express the acidity of a solution in terms of its Ph, rather than in terms of the molarity of hydrogen ion present? How is pH defined mathematically?

Interpretation Introduction

Interpretation:

The reason for scientists to express the acidity of a solution in terms of its pH rather than in terms of the molarity of hydrogen ions present should be explained.

Concept Introduction:

It is important to have a scale to compare the strength of a property. Acidity of a certain solution is a critical parameter that one must consider in comparing reaction conditions, yields and activity of the enzymes. Therefore it is important to have an easy and understandable scale that one gets a clear idea about the acidity of a given solution.

Explanation

Assume that the [H+ (aq)] of a given solution is 10-4 M. This is typically smaller quantity in terms of concentration. But if one uses the pH scale;

pH=-log10[H3O+(aq)]

pH=-log1 0 (10-4 M) = 4

Hence it is much easier to represent the hydrogen ion concentration using the scale. Also, if one needs to compare the acidity strength of different solutions, this pH scale becomes useful.

Depending on the value of the solubility product of water the integer values which pH can attain could be limited from 1-14. Hence, chemists could get a much representative idea about the acidity by using the scale.

How the scale extends from 1 to 14 can be shown as below?

pH=-log10[H3O+(aq)]

Also,

pOH=log10[OH(aq)]

Kw =[H3O+(aq)]×[OH-(aq)] …… (1)

Here, [H3O+(aq)] is the hydronium ion concentration and [OH-(aq)] is hydroxide ion concentration.

Taking natural log on both sides of the equation (1) and multiplying both sides by negative sign

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