““Save the whales. Collect the whole Save the whales. Collect the whole set”set”

““Plan to be spontaneous tomorrow”Plan to be spontaneous tomorrow”

““Ambition is a poor excuse for not Ambition is a poor excuse for not having enough sense to be lazy”having enough sense to be lazy”

““Life is too short not to be in a hurry”Life is too short not to be in a hurry”

A.A. AnnouncementAnnouncement::http://www.columbia.

edu/itc/sipa/envp/louchouarn/courses/

B.B. SolutionsSolutions

C.C. Acid-BasesAcid-Bases::• Carbonate systemsCarbonate systems• AlkalinityAlkalinity

D.D. The legacy of acid-rain in a changing The legacy of acid-rain in a changing climateclimate

U6220: Environmental Chem. & U6220: Environmental Chem. & Tox.Tox.

Thursday, June 16 2004Thursday, June 16 2004

Polarity of moleculesBasic Chemistry ReviewBasic Chemistry Review

The C-H bond is one of the most common in organic The C-H bond is one of the most common in organic compounds. The electronegativity difference between these compounds. The electronegativity difference between these two atoms is 0.4 (weakly polar).two atoms is 0.4 (weakly polar).The electronegativity difference in the O-H bond, however, is The electronegativity difference in the O-H bond, however, is 1.4 (polar bond)1.4 (polar bond)

Dipole bonding results Dipole bonding results from polar substances in from polar substances in a polar solution a polar solution (solubility)(solubility)

Apolar molecules will Apolar molecules will tend to have low tend to have low solubility in polar solubility in polar solutionssolutions

The Water (“Mickey Mouse”) MoleculeThe Water (“Mickey Mouse”) MoleculeWater:Water: H H22O! How simple can that be?O! How simple can that be?

Dipole (slightly charged at each end!)Dipole (slightly charged at each end!) Uneven charge Uneven charge Hydrogen bonds! Hydrogen bonds!

Higher energy requirement for change of state (i.e. to “separate” Higher energy requirement for change of state (i.e. to “separate” Mickey and Minnie!)Mickey and Minnie!)

Melting-Boiling T of water

-100

-50

0

50

100

150

0 20 40 60 80 100 120 140

Molecular weight (moles)

Temperature (

oC)

H2O

H2SH2Se

H2Te

SolubilitySolubilityBasic Chemistry ReviewBasic Chemistry Review

Solubility of compounds in water (or any other liquid/solvent) Solubility of compounds in water (or any other liquid/solvent) influences their dispersal and fate in the environment (water influences their dispersal and fate in the environment (water exists in liquid form on land, under land, and in the exists in liquid form on land, under land, and in the atmosphere).atmosphere).

Solution of an ionic compound in Solution of an ionic compound in a polar solvent (ie. NaCl in a polar solvent (ie. NaCl in water). water).

SolubilityC) Basic Chemistry ReviewC) Basic Chemistry Review

Solubility of nonpolar compounds in nonpolar solvents:Solubility of nonpolar compounds in nonpolar solvents:““like” dissolves “like”like” dissolves “like”

NaCl will NOT dissolve in hexaneNaCl will NOT dissolve in hexaneBut PCBs, oil, etc, will!But PCBs, oil, etc, will!Solubility of nonpolar solutes in Solubility of nonpolar solutes in water decreases with size of water decreases with size of solutesolute

4)4) Partition behaviorPartition behavior

Basic Chemistry ReviewBasic Chemistry Review

Partition coefficient: Ratio of a concentrations of a chemical in two Partition coefficient: Ratio of a concentrations of a chemical in two different phases different phases organic pollutants - PCBs, PAHs – and lipids organic pollutants - PCBs, PAHs – and lipids

how solutes behave with respect to two solvents (polar how solutes behave with respect to two solvents (polar vsvs. non . non polar)polar)

The partition coefficient is constant for a The partition coefficient is constant for a given solute and two specific solvents given solute and two specific solvents (under constant environmental conditions: (under constant environmental conditions: T & P) T & P)

Partition coefficient is dependent on:Partition coefficient is dependent on:1)1) Polarity of solutePolarity of solute2)2) Its molecular weightIts molecular weight3)3) Relationship to the polarity of solventsRelationship to the polarity of solvents

4)4) Partition behaviorPartition behaviorBasic Chemistry ReviewBasic Chemistry Review

Octanol (CHOctanol (CH33-(CH-(CH22))77-OH)/water partition (imitates lipid/water -OH)/water partition (imitates lipid/water partition)partition)

[C][C]oo = [C] = [C]w w K Kowow

KKowow = [C] = [C]oo/[C]/[C]ww

As KAs Kowow increases, the “lipophilicity” of a chemical increases increases, the “lipophilicity” of a chemical increases

KKowow for various homologous for various homologous series is related to series is related to molecular surface area molecular surface area sizesize

Solutions

Kind of Mixture Particle Size Example CharacteristicsSolution <2.0 nm air, seawater,

gasoline, wineTranslucent, doesnot separate, non

filtrableColloid 2.0-500 nm butter, milk, fog,

humic riversOften opaque,

does not separate,non filterable (!…)

Heterogeneous >500 nm Blood, paint,sediments,aerosols

opaque or murky,separation uponstanding, filtrable

A.A. Molarity (M)Molarity (M)

Moles of solute/Liters of solutionsMoles of solute/Liters of solutions

B.B. Mass per Volume (g/L)Mass per Volume (g/L)

mass of solute/Liters of solutionsmass of solute/Liters of solutions

C.C. Mass per Mass (ppm)Mass per Mass (ppm)

mass of solute/mass of solutions (g/g)mass of solute/mass of solutions (g/g)

D.D. Mass per Mass per Volume (ppmv)Mass per Mass per Volume (ppmv)

percent volume solute/volume of solutionpercent volume solute/volume of solution

Solutions

Aquatic equilibria are important in environmental Aquatic equilibria are important in environmental processesprocesses

At equilibrium:At equilibrium:

Solution Equilibria and AcidsSolution Equilibria and Acids

aA + bB aA + bB cC + dD cC + dDKKcc = [C] = [C]cc[D][D]dd/[A]/[A]aa[B][B]bb

Where KWhere Kcc is the equilibrium constant and the right hand of the is the equilibrium constant and the right hand of the equation, equation, the the equilibrium quotientequilibrium quotient, is the ratio of products to , is the ratio of products to

reactantsreactants

Le Chatelier PrincipleLe Chatelier Principle (useful indications of shifts in (useful indications of shifts in equilibrium):equilibrium):““When a system in equilibrium is subjected to change, the When a system in equilibrium is subjected to change, the system will alter in such a way as to lessen the effect of that system will alter in such a way as to lessen the effect of that change”change”

Adding product ‘C’ to the system will make the rxn shift to Adding product ‘C’ to the system will make the rxn shift to the left (consumption of ‘C’ and ‘D’) and the position of the the left (consumption of ‘C’ and ‘D’) and the position of the equilibrium changes (equilibrium changes (KKcc remains unchanged) remains unchanged)

Dissociation of water and the pH scaleDissociation of water and the pH scale

2H2H22O O HH33OO++ + OH + OH--

oror

HH22O O HH++ + OH + OH--

wherewhere

KKww = ([H = ([H++]] [OH[OH--]/[H]/[H22O])O])eqeq

Where [HWhere [H22O] is equal to unity (pure substances)O] is equal to unity (pure substances)

KKww = ([H = ([H++]] [OH[OH- - ])])eqeq

Dissociation of water and the pH scaleDissociation of water and the pH scale

KKww = ([H = ([H++]] [OH[OH--]/[H]/[H22O])O])eqeq

Experimental determination shows thatExperimental determination shows that

KKww = 1.8x10 = 1.8x10-16-16 mol/liter (at 25ºC) mol/liter (at 25ºC)

It is conventional to omit the concentration of water It is conventional to omit the concentration of water from this K expression. Why?from this K expression. Why?

[H[H22O]O]eq eq = 55.5 Molar= 55.5 Molar

Why?Why?

KKww = 10 = 10-14-14

Why?Why?

Dissociation of water and the pH scaleDissociation of water and the pH scale

KKww = ([H = ([H++]] [OH[OH- - ])])eqeq

Experimental determination shows thatExperimental determination shows that

KKww = 10 = 10-14-14 (at 25ºC) (at 25ºC)

log Klog Kww = log 10 = log 10-14-14

log Klog Kww = -14 log 10 = -14 log 10

-log Klog Kww = 14 = 14

pKpKww = -log K = -log Kww

So pKSo pKww = 14 = 14

[H[H++]] [OH[OH--] = 1x10] = 1x10-14-14 and [H and [H++]] = [OH = [OH--] = 1x10] = 1x10-7-7

So pH of natural waters = -log [HSo pH of natural waters = -log [H++] = -log 10] = -log 10-7-7 = 7 = 7

Dissociation of water and the pH scaleDissociation of water and the pH scale

KKww = [H = [H++]] [OH[OH- - ]]And for any acid (HB) in solutionAnd for any acid (HB) in solution

HB HB H H++ + B + B--

€

Ka = H +[ ] × B−

[ ]( ) HB[ ]

€

LogKa = Log H +[ ] + Log

B−[ ]

HB[ ]

⎛

⎝ ⎜ ⎜

⎞

⎠ ⎟ ⎟

€

−LogKa = −Log H +[ ] − Log

B−[ ]

HB[ ]

⎛

⎝ ⎜ ⎜

⎞

⎠ ⎟ ⎟

€

pKa = pH − LogB−

[ ]

HB[ ]

⎛

⎝ ⎜ ⎜

⎞

⎠ ⎟ ⎟

€

pH = pKa + LogB−

[ ]

HB[ ]

⎛

⎝ ⎜ ⎜

⎞

⎠ ⎟ ⎟

((Henderson-HasselbachHenderson-Hasselbach equation) equation)

Dissociation of water and the pH scaleDissociation of water and the pH scaleFor waterFor water

log Klog Kww = log [H = log [H++]] + log [OH+ log [OH--]]

- log K- log Kww = - log [H = - log [H++]] - log [OH- log [OH--]]

pKpKaa = pH + pOH = pH + pOH

and and

pH + pOH = 14pH + pOH = 14

For other acids:For other acids:KKaa = [H = [H++]] [A[A- - ]/[HA]]/[HA]

HCl HCl HH++ + Cl + Cl-- where pK where pKaa = -3 = -3

CHCH33COOH + HCOOH + H22O O CHCH33COOCOO-- + H + H++

KKaa = ([CH = ([CH33COOCOO--]+[H]+[H++])/[CH])/[CH33COOH] = 10COOH] = 10-4.76-4.76

pKpKaa = ? = ?

pKpKaa = 4.76 = 4.76

Dissociation of water and the pH scaleDissociation of water and the pH scaleFor other acids:For other acids:

KKaa = [H = [H++]] [A[A- - ]/[HA]]/[HA]

HCl HCl H H++ + Cl + Cl-- where pK where pKaa = - log K = - log Kaa or K or Kaa = 10 = 10-pKa-pKa

Speciation of metalsSpeciation of metals::Species distribution based on environmental Species distribution based on environmental

conditionsconditions

What is the most abundant species of iron in natural What is the most abundant species of iron in natural waters?waters?

Single variable diagramsSingle variable diagrams

pH and mineral surface charge

The “point of zero charge” The “point of zero charge” (PZC) is point at which a (PZC) is point at which a surface charge changes surface charge changes signsign

pHpHpzcpzc will influence sorption will influence sorption capacity of minerals (and capacity of minerals (and organic substances) in organic substances) in natural environmentsnatural environments

pH and mineralspH and minerals

Single Variable Diagrams: Single Variable Diagrams: pHpH

What is the most abundant What is the most abundant species of arsenic in natural species of arsenic in natural waters?waters?

How does pH influence As How does pH influence As distribution?distribution?

Carbonate system - Acids in the Carbonate system - Acids in the environmentenvironment

COCO2(aq)2(aq) + H + H22O O = H= H22COCO33º (total º (total COCO2(aq)2(aq) + + HH22COCO33))KKCOCO22

= = [[HH22COCO3 3 ºº]/[P]/[PCOCO22] = 10] = 10-1.47-1.47

First dissociation step for carbonic acid:First dissociation step for carbonic acid:

KK11 = = [H[H++]] [[HCOHCO33- - ]/[]/[HH22COCO33] = 10] = 10-6.35-6.35

Second dissociation step for carbonic acid:Second dissociation step for carbonic acid:

KK22 = = [H[H++]] [[COCO332- 2- ]/[]/[HCOHCO33

--] = 10] = 10-10.33-10.33

Carbonate system - Acids in the Carbonate system - Acids in the environmentenvironmentDominant carbonate species are related to KDominant carbonate species are related to K11 and K and K22

HH22COCO33 dominates below pH = pK dominates below pH = pK11 = 6.35 = 6.35HCOHCO33

-- dominates between pH = pK dominates between pH = pK11 = 6.35 & pH = pK = 6.35 & pH = pK22 = 10.33= 10.33COCO33

2-2- dominates above pH = pK dominates above pH = pK22 = 10.33 = 10.33

AlkalinityAlkalinityAlkalinityAlkalinity is a measure of the ability of a water body to is a measure of the ability of a water body to neutralize acids and is very important in predicting the neutralize acids and is very important in predicting the extent of acidification in natural waters (i.e. lakes and rivers)extent of acidification in natural waters (i.e. lakes and rivers)

Alkalinity Alkalinity = = [OH[OH--] + [HCO] + [HCO33--] ] + 2[+ 2[COCO33

2-2-]] - [H - [H++]]ANC = ANC = [OH[OH--] + [HCO] + [HCO33

--] ] + 2[+ 2[COCO332-2-] + [B(OH)] + [B(OH)44

--] + [H] + [H33SiOSiO44--] ]

+ 2[HPO+ 2[HPO442-2-] + [HS] + [HS--] + [NOM] + [NOM--]] - [H- [H++] - 3[Fe] - 3[Fe3+3+] - …] - …

Contribution of all these species tends to be minimal in Contribution of all these species tends to be minimal in natural fresh waters (concentrations are too small. natural fresh waters (concentrations are too small. With the With the exception of NOM!exception of NOM!). The alkalinity tends then to be equal to ). The alkalinity tends then to be equal to ANC ANC only proton accepting species, present in substantial only proton accepting species, present in substantial concentration, are carbonates and/or hydroxyl ion.concentration, are carbonates and/or hydroxyl ion.

AlkalinityAlkalinity

Alkalinity is a Alkalinity is a capacity factorcapacity factor measure of the ability of a measure of the ability of a water sample to sustain reaction with added acid or basewater sample to sustain reaction with added acid or basepH is an pH is an intensity factorintensity factor measure of the concentration of measure of the concentration of protons (acids) immediately available for reactionprotons (acids) immediately available for reaction

Buffer capacityBuffer capacity: is the capacity of a solution (or water-rock : is the capacity of a solution (or water-rock system) to resist pH change when mixed with a more acid or system) to resist pH change when mixed with a more acid or alkaline water (rock)alkaline water (rock)

AlkalinityAlkalinityTitrationTitration: “a procedure for determining the amount of acid : “a procedure for determining the amount of acid (or base) in a solution by determining the volume of base (or (or base) in a solution by determining the volume of base (or acid) of known concentration that will completely react with acid) of known concentration that will completely react with it”it”

Acidification of a lake in a natural setting is analogous to a Acidification of a lake in a natural setting is analogous to a macro-scale titration and lakes are sometimes termed macro-scale titration and lakes are sometimes termed “buffered”, “transitional”, and “acidic” depending on their “buffered”, “transitional”, and “acidic” depending on their position on the titration curve:position on the titration curve:

AlkalinityAlkalinityAn alternative way to report alkalinity is to express it in terms of An alternative way to report alkalinity is to express it in terms of neutralization reaction between carbonate and protons and neutralization reaction between carbonate and protons and given in values of mg/L of CaCOgiven in values of mg/L of CaCO33 (or mg/L of Ca (or mg/L of Ca2+2+))

1 mg CaCO1 mg CaCO33 = 1000 g which is = 1000 g which is 1000 g/100 g/mol = 10 mol1000 g/100 g/mol = 10 mol

Since each carbonate (COSince each carbonate (CO332-2-) is capable of neutralizing two OH) is capable of neutralizing two OH--

ions 10 mol of COions 10 mol of CO332-2- is is equivalentequivalent to 20 mol proton-accepting to 20 mol proton-accepting

capacity (20 equivalents or eq). capacity (20 equivalents or eq). A sensitivity classification of water bodies may thus be A sensitivity classification of water bodies may thus be expressed in terms of alkalinity using units of mol/L of proton expressed in terms of alkalinity using units of mol/L of proton accepting capacity (eq)accepting capacity (eq)

The legacy of acid-rainThe legacy of acid-rain

Coal and Acid rainCoal and Acid rain

SOSO22 + 2OH + 2OH H H22SOSO44 2H 2H++ + SO + SO442-2-

SOSO22 + H + H22OO22 H H22SOSO44 2H 2H++ + SO + SO442-2-

NN22 + O + O2 2 2NO (>2000°C) 2NO (>2000°C)

NO + ONO + O3 3 NO NO22 + O + O2 2

NONO22 + OH + OH HNO HNO33 H H++ + NO + NO33--

Acid rainAcid rain

The main sources of acid deposition are emissions from oil and coal-burning power plants and automobiles

Acid rain?Acid rain?In the US, seven states in the Ohio valley account for ~40% of In the US, seven states in the Ohio valley account for ~40% of all SOall SO22 emissions. (emissions travel downwind to N.E.) emissions. (emissions travel downwind to N.E.)

Midwest states are the most significant emitters of NOx and Midwest states are the most significant emitters of NOx and NHNH44

Acid rain?Acid rain?In the US, SOIn the US, SO22 emissions have been declining since about emissions have been declining since about 1980 (still above background).1980 (still above background).

NOx emissions have not changedNOx emissions have not changed

Acid rain?Acid rain?Acidity of rain is neutralized by CaCOAcidity of rain is neutralized by CaCO33

Acid rain?Acid rain?

Change in stream sulfate concentrations, but Change in stream sulfate concentrations, but delayed!delayed!

Yellow: wet depositionYellow: wet depositionBlue: surface watersBlue: surface waters

Acid rain?Acid rain?Role of hydrodynamic forcingRole of hydrodynamic forcing

0

2000

4000

6000

8000

10000

12000

May-31 Aug-39 Oct-47 Jan-56 Mar-64 Jun-72 Aug-80 Nov-88 Feb-97 Apr-05

Date

St. Lawrence streamflow (m3/s)

0

200

400

600

800

1000

1200

1400

1600

1800

2000

Hudson streamflow (m3/s)

St.LawrenceSt.L AverageHudsonHud Average

Large-scale spatial variability in streamflow is explained by precipitation/evaporation balance to a large extent (~90%) and additional processes to a smaller one (soil water storage, seasonality)

Spatial Variability of Streamflow (U.S. North Spatial Variability of Streamflow (U.S. North East)East)

What are the seasonal predictions for N. America?What are the seasonal predictions for N. America?

Seasonal predictions of precipitation for North America. Clockwise from upper left: Seasonal predictions of precipitation for North America. Clockwise from upper left: WinterWinter, , SpringSpring, , FallFall, , SummerSummer. Coupled Model Intercomparison Project (CMIP) using 1% . Coupled Model Intercomparison Project (CMIP) using 1% COCO22 increase per year and the perturbations for the last 20 years of an 80 years run increase per year and the perturbations for the last 20 years of an 80 years run (Ting, pers. Comm.)(Ting, pers. Comm.)

Drought Temporal and spatial variability Drought Temporal and spatial variability

For the Catskill region, the change in evapotranspiration and snowpack amount will offset any increase in precipitation that may occur.

Temporal Variability of StreamflowTemporal Variability of Streamflow

Fluctuations in streamflow patterns (particularly Fluctuations in streamflow patterns (particularly drought incidence) has strong impact of re-drought incidence) has strong impact of re-acidification of lakesacidification of lakes Increased Al inputs (toxic to aquatic biota)Increased Al inputs (toxic to aquatic biota) Decreased pHDecreased pH Decreased acid neutralizing capacity (ANC)Decreased acid neutralizing capacity (ANC)

What does it mean for acidified lake What does it mean for acidified lake recovery?recovery?

Redox Potential (Acid Mine Drainage)Redox Potential (Acid Mine Drainage)

Sulfate reduction:Sulfate reduction:

SOSO442-2-

+ 2CH+ 2CH22O + 2HO + 2H++ H H22S + 2HS + 2H22O + 2COO + 2CO22

With the presence of FeWith the presence of Fe2+2+

FeFe2+2+ + H + H22S S FeS + 2H FeS + 2H++ And FeS + S And FeS + S FeS FeS22

FeSFeS22 + H + H22O + 7/2OO + 7/2O22 Fe Fe2+2+ + 2SO + 2SO442-2- + +

2H2H++

AndAnd

FeSFeS22 + 14Fe + 14Fe3+3+ + 8H + 8H22O O 15Fe 15Fe2+2+ + + 8H8H22SOSO44

LaterLater

4Fe4Fe2+2+ + O + O22 + 10H + 10H22O O 4Fe(OH) 4Fe(OH)33 + 8H + 8H++

Sulfide oxidationSulfide oxidation

Natural Organic Matter (Humic Matter)Natural Organic Matter (Humic Matter)- Fulvic Acids (Fa)Fulvic Acids (Fa): small fractions soluble in aqueous : small fractions soluble in aqueous solutionsolution- Humic Acids (Ha)Humic Acids (Ha): larger fractions soluble in alkaline : larger fractions soluble in alkaline sol.sol.- Humin (Hu )Humin (Hu ): larger insoluble fractions: larger insoluble fractions

Fluctuations in streamflow patterns (particularly Fluctuations in streamflow patterns (particularly drought incidence) has strong impact of re-drought incidence) has strong impact of re-acidification of lakesacidification of lakes Decrease in DOC concentrations (AlDecrease in DOC concentrations (Al3+3+ + flocculation) + flocculation) Deeper penetration of UVB (factor of 3 in some Deeper penetration of UVB (factor of 3 in some lakes)lakes)

Delayed lake recoveryDelayed lake recovery

Extra slidesExtra slides

Covalent bondsBasic Chemistry ReviewBasic Chemistry Review

Bonds in such compounds are formed by the Bonds in such compounds are formed by the sharingsharing of e of e-- rather than by the complete transfer of erather than by the complete transfer of e-- from one atom to from one atom to another.another.The eThe e-- in covalent compounds exist in molecular orbitals in covalent compounds exist in molecular orbitals formed by overlapping of two atomic orbitals.formed by overlapping of two atomic orbitals.

Sometimes, sharing two eSometimes, sharing two e-- is not enough…is not enough…

3)3) ElectronegativityElectronegativityC) Basic Chemistry ReviewC) Basic Chemistry Review

When two different atoms are joined by a covalent bond, the When two different atoms are joined by a covalent bond, the bonding ebonding e-- are not necessarily shared equally are not necessarily shared equally Atoms have Atoms have different abilities to attract edifferent abilities to attract e--

Carbonate system - Acids in the Carbonate system - Acids in the environmentenvironmentDominant carbonate species are related to Dominant carbonate species are related to KK11 and K and K2 2 - - But But

Why?Why?Remember:Remember:

KKaa = [H = [H++]] [A[A- - ]/[HA]]/[HA]log Klog Kaa = log [H = log [H++]] + log ([A+ log ([A- - ]/[HA])]/[HA])-log K-log Kaa = -log [H = -log [H++]] - log ([A- log ([A- - ]/[HA])]/[HA])

pKpKaa = pH - log ([A = pH - log ([A- - ]/[HA])]/[HA]) pKpK11 = pH - log ([HCO = pH - log ([HCO33

- - ]/[H]/[H22COCO33])])

Carbonate system - Acids in the Carbonate system - Acids in the environmentenvironmentpKpK11 = pH - log ([HCO = pH - log ([HCO33

- - ]/[H]/[H22COCO33])])At pH = pKAt pH = pK11

pKpK11 - pH = - log ([HCO - pH = - log ([HCO33- - ]/[H]/[H22COCO33])])

0 = - log ([HCO0 = - log ([HCO33- - ]/[H]/[H22COCO33])])

0 = - log[HCO0 = - log[HCO33- - ] + log[H] + log[H22COCO33]]

log[HCOlog[HCO33- - ] = log[H] = log[H22COCO33]]

[HCO[HCO33- - ] = [H] = [H22COCO33]]

What is the acidity of natural rain?What is the acidity of natural rain?

What is the acidity of natural rain?What is the acidity of natural rain?

COCO22(aq) + H(aq) + H22O = HO = H22COCO33º (total COº (total CO22 + H + H22COCO33))

KKCOCO22 = [H = [H22COCO3 3 º]/Pº]/PCOCO22

= 10 = 10-1.47-1.47 (1)(1)

First dissociation step for carbonic acid:First dissociation step for carbonic acid:

KK11 = [H = [H++]] [HCO[HCO33- - ]/[H]/[H22COCO33] = 10] = 10-6.35 -6.35 (2)(2)

So, by combining equation So, by combining equation (1)(1) and and (2)(2)

[H[H++] [HCO] [HCO33- - ] = K] = K1 1 KKCOCO22

PPCOCO22

(where P(where PCO2CO2 = 360 ppmv) = 360 ppmv)

What is the acidity of natural rain?What is the acidity of natural rain?

[H[H++] [HCO] [HCO33- - ] = K] = KCOCO22

KK1 1 PPCOCO22

(where P(where PCO2CO2 = 360 ppmv) = 360 ppmv)

Solving this yieldsSolving this yields

[H[H++]]22 = 10 = 10-1.47-1.47 x 10 x 10-6.35-6.35 x 10 x 10-3.44-3.44

[H[H++]]22 = 1x10 = 1x10-11.26-11.26

pH = ?pH = ?

[H[H++] = (1x10] = (1x10-11.26-11.26))1/21/2

[H[H++] = 10] = 10-5.63-5.63

pH = 5.63pH = 5.63