Lecture of 27 January 2020Outline of today's lecture

Need an ombudsperson for Ch14 •Activities and Debye-Huckel theory•Ionic strength, buffers and pH•Introduction to CO2 acid-base chemistry•

ionic strength effects on aciddissociationequilHA E Htt A

salt increasing salt stabilizesproducts

K Cata CHt 8 22a A CHA Tena

T pAI 8C non idealeffectsTrue Kaconstant

Debye Hickel

theory 4923

Debye Hiickel limiting law for 7 of an kin ofchargeZlogos 0.509 ZITI water 298 K

definedshortly

I E Ici 2 I ionic strength

mean ionic activity coef logcotta 0509122 ITIl

Debye Hackel limitinglaw valid to

I 0.01 M

extended D H expression

limitinglaw dlziz.LV

Empirical Davies expression for 8

log r Hz z l x TITE O ZI

Z

PH pKa log CAICHAdilute buffer by Coxexpect pH to be unchanged

pH of buffer withHpoufftp.y constant

pH decreasesasvary total phosphate phosphate

concentrator'sincreases

why

phosphate bufferKa Kau Ka

HzPoy In HzPOI T HPof poppKa's 2.2 72 12.3

KaiIka 105 Kafka 1010

aside if sites are identicaland non interactingexpect2 sites KailKaz 43 sites Kalka 3 Kalka 9

obs k173

kap 9 negative cooperativity in Ht binding

POI 3

Titration of phosphoric acid

Ty poorbather

HypoyHank HPOy pop

Hb

i

i l Ii ie l Ii pI ll ls l

pka pka pka

eachtermT T Good buffer pH

IIEE t i E kEYIt dissociated 20 I 3fromHzP0y

Species CHspoyjCHrpoylkHpoyJ 0yJPhosbaumfImono1di.I tri basic phosphett

Note when little Kaz then CHzpoy ln.CHPoy

when Hypo5 HPOy

pH 7.2T logYITYo 7.2

pH should be independentof dilutionbut it isn't

Cy

H Oui CltPoy

HIoui Itpop Ltt

CHzpor t CltPoy

tasselbaticefficientsHBZ BZ t Ht

Kao CARTAAAB

toga logKai log CEast logTft

pH pk t GE t OpkaCABnote pH metermeasures AHt

for our phosphatebuffs

opkaelogfgf.IT log8HroTH.apoy

recall logo to 0.509 ZITI2 chargeofacid EHzpai a I

can show ONKaa 10.509 Zz 1 itsigns error I I feelh

sign error in lecture correctedherehow well does this work

Ionic strength of phosphate buffer CeMC KH Poly t kit Poy2

I Ya 242Ci Zo

Kt 3 12

Hypo ez

I k Zazi

2CH Pop ez 22

Opka limits law 10.509 22 1 JEEin3

extended 8pka453

11 1.65TEEBa

Cohn JACS 4L 173 1927

CO2 acid base chemistry

CozCg CO2 aqK P e Henry's Law

many conventions seeHenry's law constant handout at end ofthesenotes

we use Plath and c M

Cozart 25 C K 0.035 Matan

Os Nz Kan 0.001 Mahn

strong T dependence at 0 C K 0.070 Math

OH co

CO2 ag t Hyo E Hz z K 1.7 10 3

Atm Azn 400ppm 4 0 4 atm

Ozlaq Ii 4 10514

Cdg 2.4 0 814

Henry Law conventions Several different conventions are used for Henry’s law, including:

kH P = c where P is in atm and c is in molar (moles/liter). or P = k x where P is in mm Hg and x is in mole fraction. or the related convention P = k'x where P is in atm and x is in mole fraction. Edsall and Gutfreund (“Biothermodynamics” book) use "Q" (Table 3.8, pg 81) which is the ratio of the molar concentration of a gas in the solution and gas phases:

Q (n/(V/1000)) = Q(P/(1000RT)) = c (the factor of 1000 converts from m3 to liters) The relationships between the various Henry law constants at 298 K maybe derived

For oxygen at 298 K, k = 3.3 x 107 (mm Hg / mole fraction) k' = 4.3 x 104 (atm / mole fraction) kH = 0.0013 (M / atm) Q = 0.0311 (M aq / M gas) For the ∆G˚ tabulated in Table 3.8 of Edsall and Gutfriend

for O2, this equals 26.5 kJ mol-1. at 298 K, RT = 2477.69 J mol-1; water concentration = 997.0479/18.01528 = 55.34 M = 1000/18.01528 = 55.51 molal

Q = 1000RTP

kH = 2478101.325

kH = 24.45kH (molar gas/molar soln)

k = 55.34× 760kH

= 42058kH

(mm Hg/mole fraction)

= 55.34× 760× 2480101.325Q

= 1.0285×106

Q

′k = 55.34kH

(atm/mole fraction)

∆G! = µ! soln (mole fraction)( )− µ! vapor (atm)( ) = RT ln ′k

= RT ln55.34kH

⎡

⎣⎢

⎤

⎦⎥ = RT ln

55.34RT101.325Q⎡

⎣⎢

⎤

⎦⎥ = 2.48ln

1353Q

⎡

⎣⎢

⎤

⎦⎥ kJ mol−1