cata cht - br.caltech.edu · lecture of 27 january 2020 outline of today's lecture • need an...
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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