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D O N E B Y : D U H A N Y U A N 3 O 1 0 6

Introduction and theApplications of pH

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What is pH?

y pH is a unit of measurement to show the degree ofacidity or alkalinity of a solution. It is measured on ascale of 0 to 14

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Origins of pH

y The term pH is made up of two characters, p & H

y p is the mathematical symbol of the negativelogarithm

y H is the chemical symbol of Hydrogen

y Thus the formal definition of pH is the negativelogarithm of the Hydrogen ion activity

y Equation of pH = -log[H+]

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pH Measurement

y A rough measurement of pH can be obtained using pH papers or indicators, whichchanges colour as the pH level varies

y These indicators have limitations on their accuracyy Some of these indicators include: universal indicator, methyl orange,

phenolphthalein, litmus papery More accurate pH measurements can be obtained with a pH meter

y A pH measurement system consists of three parts: a pH measuring electrode, areference electrode, and a high input impedance meter

y The pH electrode can be thought of as a battery, with a voltage that varies with thepH of the measured solution

y The pH measuring electrode is a hydrogen ion sensitive glass bulb, with a millivoltoutput that varies with the changes in the relative hydrogen ion concentration insideand outside of the bulb

y

The reference electrode output does not vary with the activity of the hydrogen iony The pH electrode has very high internal resistance, making the voltage change with

pH difficult to measurey The pH meter is basically a high impedance amplifier that accurately measures the

minute electrode voltages and displays the results directly in pH units on either ananalog or digital display

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Applications of pH

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Body pH Test (urinary)

y pH could also be used for testing for your urinary pH

y The pH of the urine indicates how the body isworking to maintain the proper pH of the blood and

also indicates the efforts of the body via the kidneys,adrenals, lungs and gonads to regulate body pHbalance through the buffer salts and hormones.

y The urine reveals the alkaline building (anabolic)

and acid tearing down (catabolic) cyclesy pH paper is also used for testing

y The ideal range of urinary pH is 6.5-7.0+

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Soil pH Test

y The pH of the soil is very important in sustaining the life andgrowth of vegetation

y Some crops have a preference for either alkaline or acidic soil,affecting the harvest

y The pH will also affect the availability of nutrients in the soiland there may be some diseases which thrives in a particularpH range

y Thus the first step in preparing soil is to test the pH

y Typically, when the pH level of soil is too low (acidic), lime

will be added as it is alkaline, thus neutralizing the soil.y If the pH is too high (alkaline), sulfur is added to the soil as it

is acidic, thus neutralizing the soil

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Swimming Pool pH Test

y Maintaining appropriate pH levels in swimmingpools will ensure that the pool is safe and sanitary

y An acidic pool can deteriorate the pool surfaces and

the surfaces of pool equipment and can also burn theswimmers' eyes, thus endangering swimmers

y An alkaline pool can result in calcification and canprevent the antibacterial properties of the chlorine

(this is because chlorine is acidic, thus it will beneutralized due to the alkaline waters of the pool),thus making the pool not sanitary

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pH in daily life

1. Waking up in the morning 2. Brushing teeth

How does this relate tothe application of pH?

Toothpaste is mildly alkaline in nature. It has a pH of 8.0 to 9.0.It is alkaline in nature as the plaque in the mouth produces plaque

acids and will corrode the teeth. Thus the alkaline toothpaste willneutralize the acid and prevent tooth decay.

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pH used in Food Preservation

y Lye (or sodium hydroxide) is used in food preservation

y Make the food too alkaline for bacteria to grow

y Lye will also saponify (a chemical process where soap is

formed from fatty acids derivatives) fats in the food, whichwill change the texture and flavour

y Lye is used in various foods we see today for example, oliverecipes and my personal favourite: century eggs

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pH used in Food Preservation (contd)

y Most microorganisms grow best at a pH of around 7and can't grow in an acidic environment

y Thus adding an acid like vinegar or citric acid (or in

most cases, vitamin C) will increase the acidity andlimit bacterial and fungal growth

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Conclusion

pH is a wonderful measurement that is crucial in ourlives. Without pH we will not be able to preventtooth decay. Neither will we be able to use our

swimming pools or will we be able to properly farm,and some of our wonderful preserved food will alsodisappear. Thus I feel that pH is indeed very usefuland learning about it will benefit one greatly.

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Thank You!

y Bibliography:

y http://www.ionizers.org/ph-balance.html

y http://www.ehow.com/list_6039108_practical-

uses-ph-testing.html

y http://faculty.ccri.edu/aahughes/GenChemII/Lab%20Experiments/pH_Measurement_and_Uses.pdf

y http://www.omega.com/techref/ph.html

y http://faculty.sxu.edu/~fast/bio101_lab/preservation.htm