enve 201 environmental engineering chemistry 1
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ENVE 201 Environmental Engineering Chemistry 1. pH Dr. Aslıhan Kerç. Definition of pH. Used to express the intensity of the acid or alkaline condition of a solution Express hydrogen ion concentration Express hydrogen ion activity. Why pH is important in environmental engineering?. - PowerPoint PPT PresentationTRANSCRIPT
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ENVE 201Environmental Engineering
Chemistry 1
pH
Dr. Aslıhan Kerç
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Definition of pH
• Used to express the intensity of the acid or alkaline condition of a solution
• Express hydrogen ion concentration• Express hydrogen ion activity
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Why pH is important in environmental engineering?In environmental engineering pH must be
considered in:• Chemical coagulation• Disinfection• Water softening• Corrosion control• Microorganisms in biological treatment• Sludge dewatering• Oxidation of certain substances (such as
cyanide)
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Common characteristics of Acids and Bases
• All acids contain element hydrogen• Neutralization reaction between acids- bases?
produce water• Bases contain hydroxyl groups• Strong acid ? Weak acid?• Strong acids and bases are highly ionized• Weak acids and bases are poorly ionized in
aqueous solutions.
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Hydrogen Electrode
• Used to measure hydrogen ion activity• Pure water dissociates to produce hydrogen
and hydroxyl ionsH2O H+ + OH-
H ions 10-7 mol/LOH ions 10-7 mol/LEquilibrium equation?
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Equilibrium Equation
• Since concentration of water is constant, activity =1
• {H+} {OH-}=10-7 x 10-7 = 10-14
KOH
OHH
2
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• When acid is added to water, hydrogen activity increases
• When base is added to water hydoxile ion activity increases
• {H+} and {OH-} can never be zero
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Sorenson, 1909
• pH = - log {H+}• pH range 0 -14• pH 7 @25oC represent absolute neutrality• Neutrality @ 0oC pH 7.5• Neutrality @ 60oC pH 6.5• Kw changes with change in temperature
pH of neutrality changes with temperature
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Measurement of pH
• Hydrogen electrode absolute standard for pH measurement. Not practical in use
• Indicators calibrated with hydrogen electrode. Different color characteristics at different pH levels
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Indicator pH Range Quantity per 10 ml Acid Base
Thymol Blue 1.2-2.8 1-2 drops 0.1% soln. in aq. red yellow
Pentamethoxy red 1.2-2.3 1 drop 0.1% soln. in 70% alc. red-violet colorless
Tropeolin OO 1.3-3.2 1 drop 1% aq. soln. red yellow
2,4-Dinitrophenol 2.4-4.0 1-2 drops 0.1% soln. in 50% alc. colorless yellow
Methyl yellow 2.9-4.0 1 drop 0.1% soln. in 90% alc. red yellow
Methyl orange 3.1-4.4 1 drop 0.1% aq. soln. red orange
Bromphenol blue 3.0-4.6 1 drop 0.1% aq. soln. yellow blue-violet
Tetrabromphenol blue 3.0-4.6 1 drop 0.1% aq. soln. yellow blue
Alizarin sodium sulfonate 3.7-5.2 1 drop 0.1% aq. soln. yellow violet
α-Naphthyl red 3.7-5.0 1 drop 0.1% soln. in 70% alc. red yellow
p-Ethoxychrysoidine 3.5-5.5 1 drop 0.1% aq. soln. red yellow
Bromcresol green 4.0-5.6 1 drop 0.1% aq. soln. yellow blue
Methyl red 4.4-6.2 1 drop 0.1% aq. soln. red yellow
Bromcresol purple 5.2-6.8 1 drop 0.1% aq. soln. yellow purple
Chlorphenol red 5.4-6.8 1 drop 0.1% aq. soln. yellow red
Bromphenol blue 6.2-7.6 1 drop 0.1% aq. soln. yellow blue
p-Nitrophenol 5.0-7.0 1-5 drops 0.1% aq. soln. colorless yellow
Azolitmin 5.0-8.0 5 drops 0.5% aq. soln. red blue
Phenol red 6.4-8.0 1 drop 0.1% aq. soln. yellow red
Neutral red 6.8-8.0 1 drop 0.1% soln. in 70% alc. red yellow
Rosolic acid 6.8-8.0 1 drop 0.1% soln. in 90% alc. yellow red
Cresol red 7.2-8.8 1 drop 0.1% aq. soln. yellow red
α-Naphtholphthalein 7.3-8.7 1-5 drops 0.1% soln. in 70% alc. rose green
Tropeolin OOO 7.6-8.9 1 drop 0.1% aq. soln. yellow rose-red
Thymol blue 8.0-9.6 1-5 drops 0.1% aq. soln. yellow blue
Phenolphthalein 8.0-10.0 1-5 drops 0.1% soln. in 70% alc. colorless red
α-Naphtholbenzein 9.0-11.0 1-5 drops 0.1% soln. in 90% alc. yellow blue
Thymolphthalein 9.4-10.6 1 drop 0.1% soln. in 90% alc. colorless blue
Nile blue 10.1-11.1 1 drop 0.1% aq. soln. blue red
Alizarin yellow 10.0-12.0 1 drop 0.1% aq. soln. yellow lilac
Salicyl yellow 10.0-12.0 1-5 drops 0.1% soln. in 90% alc. yellow orange-brown
Diazo violet 10.1-12.0 1 drop 0.1% aq. soln. yellow violet
Tropeolin O 11.0-13.0 1 drop 0.1% aq. soln. yellow orange-brown
Nitramine 11.0-13.0 1-2 drops 0.1% soln in 70% alc. colorless orange-brown
Poirrier's blue 11.0-13.0 1 drop 0.1% aq. soln. blue violet-pink
Trinitrobenzoic acid 12.0-13.4 1 drop 0.1% aq. soln. colorless orange-red
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Measurement of pH
• Glass electrode standard method of pH measurement. A potential is developed related to the hydrogen ion activity.
Field instrumentsBenchtop models
Standardized with buffer solutions of known pH values
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Interpretation of pH Data• pH data should be interpreted in terms of
hydrogen ion activity• Approximately we can assume
[H+] = {H+}pH + pOH = ?
= 14[H+] and [OH-] can never be zero
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• pOH or hydroxy ion activity is important in precipitation reactions involving formation of hydroxides
e.g. Precipitation of Mg2+ in softening of water with lime