## Dr. SaMeH S. Ahmed

Associate Prof. of Environmental Engineering

# pH

In chemistrypH (Potential Hydrogen) is a measure of the acidity or basicity of an aqueous solution. Pure water is neutral, with a pH close to 7.0 at 25 °C (77 °F). Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic oralkaline. pH measurements are important in medicinebiologychemistryagricultureforestryfood scienceenvironmental science,oceanographycivil engineering and many other applications.

In a solution pH approximates but is not equal to p[H], the negative logarithm (base 10) of the molar concentration of dissolvedhydronium ions (H3O+); a low pH indicates a high concentration of hydronium ions, while a high pH indicates a low concentration. This negative of the logarithm matches the number of places behind the decimal point, so, for example, 0.1 molar hydrochloric acid should be near pH 1 and 0.0001 molar HCl should be near pH 4 (the base 10 logarithms of 0.1 and 0.0001 being −1, and −4, respectively). Pure (de-ionized) water is neutral, and can be considered either a very weak acid or a very weak base, giving it a pH of 7 (at 25 °C(77 °F)), or 0.0000001 M H+. The pH has no upper or lower limit and can be lower than 0 or higher than 14, although with water, it is limited by the acidity and basicity of water. For an aqueous solution to have a higher pH, a base must be dissolved in it, which binds away many of these rare hydrogen ions. Hydrogen ions in water can be written simply as H+ or as hydronium (H3O+) or higher species (e.g., H9O4+) to account for solvation, but all describe the same entity. Most of the Earth's freshwater bodies surface are slightly acidic due to the abundance and absorption of carbon dioxide. in fact, for millennia in the past, most fresh water bodies have had a slightly acidic pH.

However, pH is not precisely p[H], but takes into account an activity factor. This represents the tendency of hydrogen ions to interact with other components of the solution, which affects among other things the electrical potential read using a pH meter. As a result, pH can be affected by the ionic strength of a solution—for example, the pH of a 0.05 M potassium hydrogen phthalate solution can vary by as much as 0.5 pH units as a function of added potassium chloride, even though the added salt is neither acidic nor basic

### pH

pH is defined as minus the decimal logarithm of the hydrogen ion activity, aH+, in a solution.[14]

$mathrm{pH} = - log_{10}(a_{ extrm{H}^+}) = log_{10}left(frac{1}{a_{ extrm{H}^+}} ight)$

This definition was adopted because ion-selective electrodes, which are used to measure pH, respond to activity. Ideally, electrode potential, E, follows the Nernst equation, which, for the hydrogen ion can be written as

$E = E^0 + frac{RT}{F} ln(a_{ extrm{H}^+})=E^0 - frac{RT}{F} pH$

where E is a measured potential, E0 is the standard electrode potential, R is the gas constantT is the temperature in kelvinsF is the Faraday constant. For H+ number of electrons transferred is one. It follows that electrode potential is proportional to pH when pH is defined in terms of activity. Precise measurement of pH is presented in International Standard ISO 31-8 as follows:[15] A galvanic cell is set up to measure the electromotive force (e.m.f.) between a reference electrode and an electrode sensitive to the hydrogen ion activity when they are both immersed in the same aqueous solution. The reference electrode may be a silver chloride electrode or a calomel electrode. The hydrogen-ion selective electrode is a standard hydrogen electrode.

Reference electrode | concentrated solution of KCl || test solution | H2 | Pt

Firstly, the cell is filled with a solution of known hydrogen ion activity and the emf, ES, is measured. Then the emf, EX, of the same cell containing the solution of unknown pH is measured.

$ext{pH(X)} = ext{pH(S)}+frac{E_ ext{S} - E_ ext{X} }{z}$

The difference between the two measured emf values is proportional to pH. This method of calibration avoids the need to know the standard electrode potential. The proportionality constant, 1/z is ideally equal to $frac{1}{2.303RT/F}$ the "Nerstian slope".

To apply this process in practice, a glass electrode is used rather than the cumbersome hydrogen electrode. A combined glass electrode has an in-built reference electrode. It is calibrated against buffer solutions of known hydrogen ion activity. IUPAC has proposed the use of a set of buffer solutions of known H+ activity.[14] Two or more buffer solutions are used in order to accommodate the fact that the "slope" may differ slightly from ideal. To implement this approach to calibration, the electrode is first immersed in a standard solution and the reading on a pH meter is adjusted to be equal to the standard buffer's value. The reading from a second standard buffer solution is then adjusted, using the "slope" control, to be equal to the pH for that solution. Further details, are given in the IUPAC recommendations.[14] When more than two buffer solutions are used the electrode is calibrated by fitting observed pH values to a straight line with respect to standard buffer values. Commercial standard buffer solutions usually come with information on the value at 25 °C and a correction factor to be applied for other temperatures. pH is an example of an acidity function. Hydrogen ion concentrations can be measured in non-aqueous solvents, but this leads, in effect, to a different acidity function, because the standard state for a non-aqueous solvent is different from the standard state for water. Superacids are a class of non-aqueous acids for which the Hammett acidity functionH0, has been developed.

pH in its usual meaning is a measure of acidity of (dilute) aqueous solutions only.[1] Recently the concept of "Unified pH scale"[16] has been developed on the basis of the absolute chemical potential of the proton. This concept proposes the "Unified pH" as a measure of acidity that is applicable to any medium: liquids, gases and even solids.

### Office hours

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Tuesday:     10-12

Wednesday: 10-11

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### Civil Eng. Students

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As we approaching the second midterm exams..  Get ready and remember our offices are open to answer you . do not hesitate to .contact me if you have difficulties

For CE 370 students : I do apologize for did not attend the extra lab session that proposed to be on Wednesday at 6 am.  Sorry

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### Announcements

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Please visit the  announcement box for the relevant course and make sure that you can download and upload easily, otherwise

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There will be an orientation session in the midell of this term to help you select your track in Civil and Environmental Engineering

### Event

#### Special Issue

Published Online on January 2016

### Mining Engineering

Mining engineering is an engineering discipline that involves practice, theory, science, technology, and the application of extracting and processing minerals from a naturally occurring environment. Mining engineering also includes processing minerals for additional value.

### Environmental Engineering

Environmental engineers are the technical professionals who identify and design solutions for    environmental problems. Environmental engineers provide safe drinking water, treat and properly dispose of wastes, maintain air quality, control water pollution, and remediate sites contaminated due to spills or improper disposal of hazardous substances. They monitor the quality of the air, water, and land. And, they develop new and improved means to protect the environment.

### Proverb

Actions speak louder than words

### Univeristies

Universities I've worked in

Assuit University (Home University), Egypt

Imperial College, London, UK

King Saud University, KSA

,Majmaah University

## My Academic Pages

https://www.researchgate.net/profile/Sameh_Ahemd

and give me

### Think

How many red balls we need to make balance

### Sports

Egypt vs Tunisia (Handball final)  30/1/2016

### Course 2016/17-1

1. Computer Applications in Surveying  CE 473
2. Surveying 1 CE 370
3. Photogrammetry CE 474
4. Surveying II  CE 371
5. Design I  (round 4) CE 498

Rule #7

### Latest

Member of the Editorial Board: " Journal of Water Resources and Ocean Sciences"  2013

Participating in The Third International Conference on Water, Energy and Environment,(ICWEE) 2015 - American University of Sharjah, UAE 24-26 March 2015 with a Paper and Poster

New article

Recovery of Titania from Waste-Sludge of Majmaah Water Treatment Plant

"Production of Titania Nano-particles from Wast-

Sludge

### Coming soon

Results of M2 CE311

### Student Conference

Participation  in the 6Th Student Conference

With a paper and oral presentation

From the Senior Design Project CE499 -35

See inside, the paper, and presentation

## Surveying  I -  CE 370 - 2016-2017-1

 Power point Sheets Lecture notes Second Midterm Exam Results Model Answer

Student Performance Records

## Surveying II - CE 371 - 2016-2017-1

 Lectures First midterm exam Lab Results

See Inside

Student Performance Records

## CE 473

 Lecturers Power point Sheets Exams + Quizzes Results

### 2015-2016-2 - Photogrammetry  CE474

 Available 0-1-2-3-4 Power point Available Quizzes 2 and 3 with model Answer Quizzes Available Chapter 1,2,3,4,5 Lecture notes Report 1  Cameras Report Y 60 marks Exams

See Inside

Student Performance Records

## Environmental Engineering 1

CE 360: Environmental Engineering 1

37-2

 Y PP0-1-2-3,4 Power point Y 1,2,3,4,5 Chapters Water quality Poster + Climate Change Reports will be announced (Quiz #2 will be using D2L- Online Quizzes Y Quizzez 2,3 and 4 with model answer and results Exams and results

### Engineering Report Writing

GE 306: Engineering Report Writing

### Senior Design 2 - CE 499

Meeting on 14-4-2015

Second Best paper from Senior Design Projects in 2015

Paper title:

### Evaluation of Groundwater Quality Parameters using Multivariate Statistics- a case Study of Majmaah, KSA

Students:

Abdullah A. Alzeer

Husam K. Almubark

Maijd M. Almotairi

### CE 360-Summer Course

Environmental Engineering I

## Welcome to CE360 second Term 2015-2016

### Engineering Practice

Engineering Practice GE 307

### What is your opinion

See what can you get from Google!! more than translation and locations

### Contact me

Mobile: 00966598311652

s.mohamed@mu.edu.sa

### Thank you

Your frequent visit to my website has helped  a lot to get the 2nd place in the university competition in the  year 1434-2013... Thanks very mush and please keep following my work

زيارتكم المتكررة لموقعي ساهمت في حصولي على المركز الثاني لاحسن المواقع الشخصية بجامعة المجمعة ...لكم جميعا خالص شكري وتقديري

## CE 212

 Y from PP0 to PP 6 + PDF Power points Y Midterm #2 + Model Answer + results Exams Y lab 3 Labs Solution of Quiz 4 + Results HW

## CE 311

M2+ model Answer + PP 1-9 = PDF 1-9 all are available

Sheets 2 + 4 with model Answers

Results of M2

### إحصائية الموقع

عدد الصفحات: 1412

البحوث والمحاضرات: 1541

الزيارات: 51449