[PDF] DETERMINATION OF ALKALINITY OF NATURAL WATERS





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Alkalinity Alkalinity is a chemical measurement of a waters ability to

As mentioned previously alkalinity in natural waters is primarily due to carbonate species and the following set of chemical equilibria is established in 



Alkalinity

Chemical reactions. Sulfuric acid (hydrochloric acid may be used) reacts with the three forms of alkalinity converting them to water or carbonic acid.



7.0 EXPERIMENT ON DETERMINATION OF ALKALINITY OF WATER

Alkalinity as carbonate and bicarbonate of saline water is very important in tertiary recovery processes for recovering petroleum. Alkaline water offers better.



DETERMINATION OF ALKALINITY OF NATURAL WATERS

THEORY. As mentioned previously alkalinity in natural water is due primarily to carbonate species. The following set of chemical equilibria is established:.



pH Alkalinity of Water

pH Alkalinity HCl(Borax). Advisable syringe. 10 mL (Hamilton). Sample. Name. Water ? 1. Amount. 100. [mL]. QC. Name. QC Sample. Electrode. Type.



1 Answer: pH 11 => All three types of alkalinity; pOH=14-pH = 14-11

7 févr. 2012 specific gravity of 2.65 in water at 20°C? Comment on settling behaviour of this type of particles. µ=1.001×10-3 N.s/m2 at 20°C.



Alkalinity

Scope and application: For water wastewater and seawater. The primary forms of alkalinity in water are hydroxide



Alkalinity

acidification US EPA has monitored regional surface water alkalinity and has The following forms of alkalinity can be determined and reported:.



Name of Faculty:Dr. Anjali Tiwari Designation: Professor Department

turbidity as it can affect brightness and colour of paper; alkalinity as it “Water treatment” is the process by which all types of undesirable ...



The alkalinity of a solution may be defined as the capacity for solutes

Several different solute species contribute to the alkalinity of water as defined above and titration with acid does not specifically identify them.



Alkalinity - Whitman College

To determine the alkalinity a known volume of water sample is titrated with a standard solution of strong acid to a pH value in the approximate range of 4 to 5 Titrations can distinguish between three types of alkalinity; carbonate bicarbonate and total alkalinity



URI pH and Alkalinity - University of Rhode Island

Alkalinity comes from rocks and soils salts certain plant activities and certain industrial wastewater discharges (detergents and soap-based products are alkaline) If an area’s geology contains large quantities of calcium carbonate (CaCO3 limestone) water bodies tend to be more alkaline



Alkalinity - Kennesaw State University

Total alkalinity is measured by titrating (step-wise addition of reagent) the water sample with sulfuric acid (H2SO4) to a pH endpoint of ~4 5 Once the water sample reaches a pH of 4 5 the three main forms of alkalinity (bicarbonate carbonate and hydroxide) have been neutralized



Searches related to types of alkalinity of water PDF

to alkalinity are carbonate bicarbonate and hydroxide Alkalinity may also include contributions from borates phosphates silicates or other bases Why measure alkalinity? Alkalinity measurement is important in many environmental and industrial applications such as: Water quality

What are the three types of alkalinity?

Titrations can distinguish between three types of alkalinity; carbonate, bicarbonate, and total alkalinity. Carbonate alkalinity is determined by titration of the water sample to the phenolphthalein indicator endpoint, or approximately a pH of 8.3.

What is the alkalinity of water?

1.2 The alkalinity of water is its acid-neutralizing capacity, comprised of the total of all titratable bases. Alkalinity is a measure of the sum of properties of water, and can be interpreted in terms of specific substances only when the chemical composition of the sample is known.

How is alkalinity measured?

One common method the U.S. Geological Survey (USGS) uses for measuring alkalinity is to use take a water sample and to add acid to it while checking the pH of the water as the acid is added. An initial pH reading of the water is taken and then small amounts of acid are added in increments, the water is stirred, and the pH is taken.

What is the pH at equivalence point of alkalinity?

When alkalinity is due predominately to carbonate or bicarbonate, as in fresh waters, the pH at the equivalence point is determined by the concentration of carbon dioxide (CO 2) at that point. The concentration of CO 2depends upon the total carbonate species originally present.

  • Past day

21

DETERMINATIONOFALKALINITY

OFNATURALWATERS

Purpose:Todeterminethealkalinityof anaturalwater samplebytitration

BACKGROUND

Alkalinityisachemical measurementofa waterÕsability toneutralizeacids. Alkalinityis alsoameasure ofawaterÕ sbuf feringcapacityor itsabilityto resist changesinpH upontheaddition ofacids orbases.The alkalinityofnatural waters isdue primarilytothe presenceofweak acidsalts,although strongbasesmay also contributeinindustrialwaters(i.e., OH ).Bicarbonatesrepresent themajorform ofalkali nityinnaturalwatersand arede rivedfromthepartition ingofCO 2 fromthe atmosphereandthe weatheringofcarbonate mineralsinrocks andsoil. Othersalts ofweakacids, suchasborate, silicates,ammonia,phosphates, andorganic bases fromnaturalor ganicmatter, maybepresentinsmallamounts. Alkalinity,by convention,isreportedasmg/LCaCO 3 ,sincemost alkalinityisderi vedfrom the weatheringofcarbonate mineralsratherthan fromCO 2 partitioningwiththe atmo- sphere.Alkalinityfor naturalwater(in molarunits)is typicallydeÞ nedasthe sum ofthecarbonate, bicarbonate,hydroxide, andhydroniumconcentrations suchthat

½alkalinity#¼2½CO

2! 3 #þ½HCO 3 #þ½OH #!½H 3 O #ð21-1Þ Alkalinityvalues canrangefromzerofromacid rainÐaffectedareas, toless than20mg/L forwatersin contactwithnon-carbonate-be aringsoils,to 2000to EnvironmentalLaboratoryExercisesfor InstrumentalAnalysisandEnvironmental Chemistry

ByFrankM. Dunniv ant

ISBN0-471-48856-9 Copyright#2004JohnW ileyð Sons,Inc. 245

4000mg/Lfor watersfromthe anaerobicdigestorsof domesticwastewater

treatmentplants(Pohland andBloodgood,1963). Neitheralkalinitynor acidity,the converse ofalkalinity,hasknown adverse healtheffects, althoughhighlyacidicoralkalinewaters arefrequentlyconsidered unpalatable.Howe ver,alkalinitycanbeaffectedbyoraffectotherparameters. Belowaresomeofthe mostimportant effectsof alkalinity.

1.Thealkalinity ofabody ofwater determineshow sensitive thatwaterbody

istoacidic inputssuchas acidrain.A waterwithhigh alkalinitybetter resistschangesin pHuponthe additionofacid (fromacidrain orfrom an industrialinput).W ediscussthis furtherwhenwediscusstherele vant equilibriumreactions.

2.Turbidity isfrequentlyremovedfrom drinkingwaterby theaddition of

alum,Al 2 (SO 4 3 ,tothe incomingwaterfollo wedbycoagulation, ßoccula- tion,and settlingina clariÞer.ThisprocessreleasesH intothewater throughthereaction Al 3þ

þ3H

2

O!AlðOHÞ

3

þ3H

ð21-2Þ

Foreffective andcompletecoagulationtooccur,alkalinitymustbepresent inexcess ofthatreactedwiththeH releases.Usually, additionalalkalinity, inthe formofCa(HCO 3 2 ,Ca(OH) 2 ,orNa 2 CO 3 (sodaash),is addedto ensureoptimumtreatment conditions.

3.Hardwaters arefrequently softenedbyprecipitation methodsusingCaO

(lime),Na 2 CO 3 (sodaash), orNaOH.The alkalinityofthe watermustbe knowninordertocalculate thelime, sodaash,or sodiumhydroxide requirementsfor precipitation.

4.Maintainingalkalinity isimportantto corrosioncontrolin pipingsystems.

Corrosionisof littleconcernin moderndomesticsystems, butman ymain waterdistribution linesandindustrialpipesaremade ofiron.Lo w-pH waterscontainlittle tonoalkalinity andleadto corrosioninmetal pipe systems,whichare costlytoreplacement.

5.BicarbonateðHCO

3

ÞandcarbonateðCO

2! 3

Þcancomplex otherelementsand

compounds,alteringtheir toxicity,transport, andfatein theenvironment.In general,themost toxicformof ametalis itsuncomplex edhydrated metal ion.Complexation ofthisfreeionbycarbonate speciescanreduce toxicity.

THEORY

Asmentionedpre viously,alkalinity innaturalwaterisdueprimarilytocarbonate species.Thefollo wingsetof chemicalequilibriaisestablished: CO 2 þH 2 O,H 2 CO 3

ð21-3Þ

H 2 CO 3 ,HCO 3 þH

ð21-4Þ

HCO 3 ,CO 2! 3 þH

ð21-5Þ

246DETERMINATIONOFALKALINITYOFNATURALWA TERS

whereH 2 CO 3 representsthetotal concentrationofdissolv edCO 2 andH 2 CO 3

Reaction(21-3)represents theequilibriumof CO

2 inthe atmospherewith dissolvedCO 2 inthewater .Theequilibrium constant,usingHenryÕslaw ,for thisreactionis K CO 2 ½H 2 CO 3 P CO 2

¼4:48)10

!5

M=mmHgð21-6Þ

Theequilibriume xpressionsfor reactions(21-4)and(21-5)are K 1 ½H #½HCO 3 ½H 2 CO 3

¼10

!6:37

ð21-7Þ

K 2 ½H #½CO 2! 3

½HCO

3

¼10

!10:32

ð21-8Þ

Asyoucan seefromequations (21-6)to (21-8),theimportant speciescontributing toalkalinityare CO 2! 3 ,HCO 3 ,andH 2 CO 3 ,andeach ofthesereactions istied stronglytopH. To illustratetheimportance oftheserelations,wewillcalculate thepHof naturalrainwaterfalling throughEarthÕsatmospherethat currently contains380ppm CO 2

First,wecon vertthe concentrationofCO

2 intheair tomol/L (step1),and then calculateitspartial pressureforuse inequation(21-6) (step2). Thisenablesus to calculatethe molarityofcarbon dioxideinwater [the[H 2 CO 3 ]termin equation (21-6)](step3), andthenthe molarityofH 2 CO 3 inthewater (step4).Finally ,we calculatethe pHofthe water,based ontheequilibrium establishedbetweenthe differentspeciesofdissolved carbonate(step4).

Step1:

densityofair ¼0:001185g=mLð1000mL=LÞ¼1:185g=L CO 2

ðairÞ¼380mgCO

2 =kgair

¼380mgCO

2

¼0:450mgCO

2 =L

0:450mg=Lð1g=1000mgÞð1molCO

2 =44gCO 2

¼1:02)10

!5 MCO 2 inair

Step2:UsingPV¼nRT(notethatn=V¼M)giv esus

P CO 2

¼MRT¼ð1:02)10

!5

¼2:50)10

!4 atm

THEORY247

Step3:UsingK

CO 2

¼½CO

2 H 2 O =P CO 2

¼4:48)10

!5

M=mmHgyields

P CO 2

ðmmHgÞ¼2:50)10

!4 atmð760mmHg=atmÞ¼0:19mmHg K CO 2

¼4:48)10

!5

M=mmHg¼M

CO 2 =P CO 2 M CO 2 inwater¼4:48)10 !5

M=mmHgð0:19mmHgÞ

¼8:52)10

!6 MCO 2

Step4: Fromstep 3,CO

2

ðaqÞ¼8:52)10

!6 M; CO 2

ðgÞþH

2 O,H 2 CO 3

K¼1:88

K¼ ½H 2 CO 3 CO 2

ðaqÞ

½H 2 CO 3 #¼1:88ð8:52)10 !6 MÞ

¼1:6)10

!5 MH 2 CO 3 Step5: Now,solvingforpHusingthe equilibriumexpression forH 2 CO 3 ,we obtain H 2 CO 3 þH 2 O,H 3 O

þHCO

3 K a

¼4:2)10

!7 K a

¼4:2)10

!7 ½H 3 O #½HCO 3 ½H 2 CO 3

4:2)10

!7 x 2

1:6)10

!5 !x andusingthe quadraticequationto solve forxyields x¼½H 3 O #¼2:59)10 !6 pH¼5:59pHof naturalrainwater Wecanalsosolv eforthe remainingchemicalspecies usingequilibrium equations.

½HCO

3 #¼xalso;so½HCO 3 #¼2:59)10 !6 MHCO 3 ½H 2 CO 3 #¼1:6)10 !5

ðtotalcarbonicconcentration Þ

!2:59)10 !6

¼1:3)10

!5 M HCO 3 þH 2 O,CO 2! 3 þH 3 O K a

¼4:8)10

!11

½CO

2! 3 #¼4:8)10 !11 M

248DETERMINATIONOFALKALINITYOFNATURALWA TERS

Summarizingyields

½H 3 O #¼2:59)10 !6

MpH¼5:59

½H 2 CO 3 #¼1:6)10 !5 M

½HCO

3 #¼2:59)10 !6 M

½CO

2! 3 #¼4:88)10 !11 M Thus,apH valueof lessthan5.6 forarainorsnow sampleisdue tomineral acidsfromatmospheric pollutionorvo lcanicemissions.Interaction oflessacidic precipitationwithsoil mineralsusuallyadds alkalinityandraises thepH value, whichcounteractsthe useofcarbon dioxidebyalgae duringdaylighthours. Ifthe consumptionrateof CO 2 isgreaterthan itsreplacementrate fromtheatmosphere, ascanoccur whenacidprecipitation isinput,the dissolvedCO 2 concentrationin thesurface waterandgroundwater willfalland resultina shifttothe leftfor the correspondingequilibriumreactions: CO 2

ðaqÞþH

2 O,H 2 CO 3 H 2 CO 3 þH 2 O,HCO 3 þH 3 O Thiswillalso resultin anincreasein thepHof thewater. AsthepH continuesto increase,thealkalinity changeschemicalspecies toreplace theCO 2 consumedby thealgae.Note theequilibriumshifts towardincreased CO 2 concentrations,which isillustratedin thefollowing reactions 2HCO 3 ,CO 2! 3 þH 2

OþCO

2 CO 2! 3 þH 2 O,2OHquotesdbs_dbs14.pdfusesText_20
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