Acid-Base Equilibria

Transcription

1 Tdeusz Górecki Ionic Equiliri Acid-Bse Equiliri Brønsted-Lory: n cid is proton, se is. Acid Bse ( 3 PO 4, O), ( N 4 ) nd ( PO - 4 ) cn ll ehve s cids. Exmple: 4 N N3 Sustnces hich cn ehve oth s cids nd s ses:, or sustnces (e.g. O, S - ). S cid S se S se cid Free protons in ny solvent, thus the ove rections re. In relity: 4 N O N3 3O Energy required to dissocite to nd : kcl/mol S Pge

2 Tdeusz Górecki Ionic Equiliri Equilirium constnt for : A 3 O O A A A : O B O B Reltionship eteen nd : B O B Leis: n cid is n ; se is n. Strength of cids nd ses SO 4 O 3O SO4 O O O O N 3 O O N cid 1 se cid se1 O SO SO O O O 3 Pge 1 3 3

3 Tdeusz Górecki Ionic Equiliri 3 O N N vlue of mens tht the cid is, thus: of ter: O O Equilirium constnt using : Activity of ter is y thermodynmic convention proportionl to the of ter in the solution. In dilute solutions it is close to. Activity of ter cn e : O O γ O γ O " " constnt: O O / γ γ γ γ Pge

4 Tdeusz Górecki Ionic Equiliri At 5, p, nd the neutrl point is p. At 5 in 3 M NlO 4 p, nd the neutrl point is p. Pge 3

5 Tdeusz Górecki Ionic Equiliri solvents: At -6, the equilirium constnt is: N3 N N N N N Thus, the p scle (defined s -logn 4 ) in liquid mmoni rnges from _ to. p of strong cid Initilly P, or " ", defined s P -log Tody's definition of p: p p log log( γ ) Generl pproch Exmple: l Mss lnce: Ion product of ter: l O hrge lnce: O l Solution: A This is qudrtic eqution, hich pplies. When, (O - is ) At higher ionic strength, ctivity coefficient should e used. Pge 4

6 Tdeusz Górecki Ionic Equiliri Strong se: Exmple: NO Mss lnce: Ion product of ter: hrge lnce: N 14 O 1 Solution: Bsic solution, thus, nd in generl Exmple: p of 7 1 M solution of NO mol / L p Simplified eqution: p Pge 5

7 Tdeusz Górecki Ionic Equiliri p of strong cid/se s function of concentrtion: log log (cid) p log (se) Mixture of strong cid nd strong se Exmple: l nd NO Mss lnce: l Mss lnce: N 14 Ion product of ter: O 1 hrge lnce: N l O When the cid nd the se re : O 1 mol / L 7 Pge 6

8 Tdeusz Górecki Ionic Equiliri Titrtion of Strong Acids nd Bses olume of the system chnges, thus must e tken into mss lnces rther thn. Exmple: titrtion of l ith NO: Mss lnce: l ( ) Mss lnce: N ( ) 14 Ion product of ter: O 1 hrge lnce: N l O At the equivlence point, (1:1 stoichiometry) nd Before the equivlence point, : After the equivlence point, : ( ) Pge 7

9 Tdeusz Górecki Ionic Equiliri Pge 8 In the vicinity of the equivlence point (.1 M, 5 ml,. M): p O- neglected Full eqution neglected Plotting the titrtion curve titrted ith : / / Titrtion of ith : / /

10 Tdeusz Górecki Ionic Equiliri Exmple: Titrtion curve p titrtion: l titrted ith NO Λ λ λ N N λ O O λ l l 1 1 Λ - conductnce ( k Ω cm ) λ - conductnce. X At 5, conductnces λ re: Procedure: the vlues of p; λ N λ O λ l λ Pge 9

11 Tdeusz Górecki Ionic Equiliri nd O - ; clculte from the eqution; clculte N /( ) (from ); clculte l /( ) (from ). 5 ml.1 M l titrted ith. M NO: onductnce ml.1 M l titrted ith.1 M NO: onductnce Pge 3

12 Tdeusz Górecki Ionic Equiliri Titrtion error Titrtion error ep ep - t ' - t Titrtion of 5 ml.1 M l ith. M NO: ' ' Enlrged section (end point detected ith t p 5): Pge 31

13 Tdeusz Górecki Ionic Equiliri Titrtion error: ml.1 M l titrted ith.1 M NO: Titrtion error: Grn plots Titrtion of ith : Before the equivlence point, is negligily smll, thus: ( ) Pge 3

14 Tdeusz Górecki Ionic Equiliri or f 1 ( )1 p, nd re, thus plot of f 1 s function of should e ith slope of intersecting the X xis t the,. Exmple: 5 ml.1 M l titrted ith. M NO: f ml In the vicinity of the equivlence point: f Pge 33

15 Tdeusz Górecki Ionic Equiliri Wek monoprotic cids nd ses A A A A O B O B B O B p p p Pge 34

16 Tdeusz Górecki Ionic Equiliri N 4 : N 3 : Dependence of on : A A γ p p log γ γ log γ γ γ γ γ logγ Using nd setting logγ I (ctivity coefficient for n ): I p ' I I I 1 here ' is the (usully.). Pge 35

17 Tdeusz Górecki Ionic Equiliri Best fit: Temperture dependence of p : Pge 36

18 Tdeusz Górecki Ionic Equiliri Pge 37 lculting the p of ek cid non: Unknon: A A O Mss lnce: A A A hrge lnce: O A A A A A A 1 A A From : A A From : O Sustituting nd into : A Thus: ) ( 3 A

19 Tdeusz Górecki Ionic Equiliri Simplifying ssumption: is negligily smll A A When : A A A Flood's digrm From nd : A Flood's digrm p log -4-6 Strong cid p4.75 p7.53 p1.7-8 Pge 38

20 Tdeusz Górecki Ionic Equiliri Degree of dissocition A A Degree of : α Degree of : A A A A A A A A 1 α A A A A Degree of dissocition nd formtion degree of formtion degree of dissocition p Pge 39

21 Tdeusz Górecki Ionic Equiliri Sillén's digrm (, ) Acetic cid,.1 M, p A - -4 log A O - p 1. is determined from the : log p. O - is determined from : log O log p p 3. A - is determined from nd : A A 4. A is determined from nd : A A Pge 4

22 Tdeusz Górecki Ionic Equiliri p of given system cn e determined from the : A O Acidic solution, thus cn e neglected A Solution for the proton condition cn e esily found on equilirium digrms using the : log ( A O ) Acetic cid, M, p A - -4 Pointer log A -1-1 O p Pge 41

23 Tdeusz Górecki Ionic Equiliri Acetic cid, M, p O A Pointer A Plotting equilirium digrms 1. nd O - : lines t (slopes of nd, respectively). A - : for A A A A log A log p A p d log A dp 1 for A A Pge 4

24 Tdeusz Górecki Ionic Equiliri 3. A: for A A A A for A A log A log p A p d log A dp 1 4. When : A A A log A log A log Wht is the p of.1 M NAc? :, thus : A log A A O A O log log A.3 Pge 43

25 Tdeusz Górecki Ionic Equiliri - -4 log oncentrtion M p Pge 44

26 Tdeusz Górecki Ionic Equiliri Wht hppens hen the cid concentrtion is?.1 M F, p 3.17 Proton condition: F O F O - log F F p Pge 45

27 Tdeusz Górecki Ionic Equiliri O - log F F - Pointer p p hecking the results: p O - F 3.6 F F Mss lnce: F F Algeric solution: A p Pge 46

28 Tdeusz Górecki Ionic Equiliri Lo concentrtions of very ek cids: 5 x 1-5 M N, p O - -4 N N - log -6-8 N - O p Mixture of cids Strong cids represented y. Strong ses represented y. Typiclly on Equiligrps. Ech or represented y the expressions: A A B B p found t the point here. Pge 47

29 Tdeusz Górecki Ionic Equiliri.1 M Ac ( ) nd.1 M Fo ( ) Ac Ac - -4 Fo Fo - log -6-8 Ac - Fo - O O - p Proton condition: Pointer function: log Ac Pointer p3.3 Ac - Fo Fo O p Pge 48

30 Tdeusz Górecki Ionic Equiliri Pge 49 Assumptions: negligily smll f f f f f f Itertion: f f f irculr reference: f f f Mixture of strong nd ek cid:.1 M l nd.1 M Ac O l Ac l l Solution: p

31 Tdeusz Górecki Ionic Equiliri Ac - l - log -6-8 Ac - l - O - Ac O - p Slt of ek cid nd ek se To independent linked y the condition tht they hve the sme. A 1 A B B O lnces: A A B B lnce: B A O : A O B Pge 5

32 Tdeusz Górecki Ionic Equiliri If nd O - : p on (provided the ssumption ove is fulfilled)! Exmple: p of.1 M N 4 Ac (p , p 9.5) p / ( p p ) 1 1 The vlue of is coincidentl. Equilirium digrm: Ac - N 4 log -8 N 3 Ac -1-1 O p Pge 51

33 Tdeusz Górecki Ionic Equiliri Pointer function: Ac - N 4 log -6-8 N 3 Ac O - Pointer p7 p Full solution: eqution in. 1 The eqution is, thus: Pge 5

34 Tdeusz Górecki Ionic Equiliri Exmple: Dimethylmmonium cette p ( ), p 1.76 ( ) p p log Generl eqution for the titrtion curve lnce: lnce: A A N A A lnce: N A O Pge 53

35 Tdeusz Górecki Ionic Equiliri Pge 54 A or A α A α Titrtion of ith : Simplifying ssumptions: efore the equivlence point ; fter the equivlence point

36 Tdeusz Górecki Ionic Equiliri Exmple: titrtion of 1 ml.1 M Ac ith.1 M NO p ( p ) ( ) ( p ) ( ) End point determined y the of the. If necessry, cn e otined in the sme mnner. : p d(p)/d Pge 55

37 Tdeusz Górecki Ionic Equiliri nd : Another y to plot the titrtion curve: through Φ: Sustitution to the generl eqution: Φ Φ ( ) Itertion set nd get the Pge 56

38 Tdeusz Górecki Ionic Equiliri p Frction titrted solution: Φ O α O p Frction titrted Pge 57

39 Tdeusz Górecki Ionic Equiliri The plot of enles esy comprisons of different. Exmples: Different of the cid p 8 6 p ml 1 Frction titrted ml 3 ml Different vlues p 6.1 M p 6.1 M 4 1e-6 4 1e-6 1e-5 1e-4 1e-5 1e-4 1 Frction titrted Pge 58

40 Tdeusz Górecki Ionic Equiliri Different : p p M.1 M.1 M.1M 1 Frction titrted p p M.1 M.1 M.1 M Different concentrtions of the : p p M.1 M.1 M.1 M 1 Frction titrted p p M.1 M.1 M.1 M Pge 59

41 Tdeusz Górecki Ionic Equiliri Titrtion of ith : α B α A Φ α α A B O O here B α ; B B B α A A A A A p 4.75 p 5.1 M p 4.75 p 5.1 M 1 ml p 8 6 p Strong se 5 1 Frction titrted 4 Strong se Pge 6

42 Tdeusz Górecki Ionic Equiliri Pge 61 Titrtion error At the equivlence point ' here is t the ' Titrtion error: ' ' '.. Φ ep ep ep ep ep e T At the equivlence point nd its vicinity: Also, ner the equivlence point,, thus 1 1 α Φ ) ( 1 1 ep α ep ) ( 1 Φ ep ep ep ep ) ( 1 Φ

43 Tdeusz Górecki Ionic Equiliri Exmple:.1 M Ac,.1 M NO, p ep insted of p t the equivlence point Φ ep 1 ()( ) Titrtion of ek se ith strong cid: Φ ep ( ) 1 ep ep ep Pge 6