Chapter 15. Applications of Aqueous Equlibria. A bag of mostly water - Star Trek -

Transcription

1 Chpter 15. Applictions of Aqueous Equlibri A bg of mostly wter - Str Trek -

2 Solutions of Acids or Bses Contining Common Ion Until now, we were concerned with the equilibrium of solution with n cid or bse. Wht will hppen in solution contining wek cid (or bse) nd its conjugte bse (or cid)? Solution conting HF (K =7. x 1-4 ) nd NF Addition of NH 4 Cl(s) into 1. M NH solution HF(q) H + (q)+f - (q) H O(l) NF(s) N + (q)+f - (q) Mjor species : HF, N +, F -, H O common ion NH (q) + H O(l) NH 4+ (q)+oh - (q) H O(l) NH 4 Cl(s) NH 4+ (q)+cl - (q) Mjor species : NH, NH 4+, Cl -, H O HF(q) H + (q)+f - (q) NH (q) + H O(l) NH 4+ (q)+oh - (q) Equlibrium (less cidic) more F - from NF Equlibrium (less bsic) more NH 4+ from NH 4 Cl Common ion effect:the shift in equilibrium tht occurs becuse of the ddition of n ion lredy involved in the equilibrium rection

3 Solutions of Acids or Bses Contining Common Ion Ex) () [H + nd % dissocition of 1. M HF (K = 7. x 1-4 ) solution? (b) [H+ nd % dissocition of solution contining 1. M HF nd 1. M NF () Mjor species : HF, H O (b) Mjor species : HF, N +, F -, H O HF(q) H + (q)+f - (q) K = 7. x 1-4 H O(l) H + (q)+oh - (q) K w = 1. x 1-14 HF(q) H + (q) + F - (q) initil x 1-7 ( ) eq 1.-x x x K 7.1 [ H 4 [ H [ F [ HF x.71 x % dissocition [ HF x 1. x M x 1..7% HF(q) H + (q)+f - (q) K = 7. x 1-4 H O(l) H + (q)+oh - (q) K w = 1. x 1-14 HF(q) H + (q) + F - (q) initil x 1-7 ( ) 1. eq 1.-x x 1.+x K [ H [ H [ F [ HF x % dissocition [ HF x 7.1 x(1. x) 1. x 4 M x(1.) 1..7%

4 Buffer Solutions Buffer solution: A solution tht resists chnge in its ph when either H + or OH - re dded. (Common ion effect is the key to mke buffer solution) Ex) () ph of buffer solution contining.5 M CH COOH (K = 1.8 x 1-5 ) nd.5 M NCH COO)? (b) ph of solution mde from dissoving.1 mol solid NOH into 1. L wter? (c) ph fter dding.1 mol solid NOH into 1. L of the solution ()? () Mjor species : CH COOH, N +, CH COO -, H O CH COOH(q) H + (q) + CH COO - (q) initil.5.5 eq.5-x x.5+x (b) Mjor species : N +, OH -, H O [ H Kw [ OH ph K [ H [ CHCOO [ CH COOH [ H x 1.81 x (5% rule : [ CH COOH ph -log( x(5. x) 5. x M M 5.M ) 4.74 x(5.) 5. 5%)

5 Buffer Solutions Buffer solution: A solution tht resists chnge in its ph when either H + or OH - re dded. (Common ion effect is the key to mke buffer solution) Ex) () ph of buffer solution contining.5 M CH COOH (K = 1.8 x 1-5 ) nd.5 M NCH COO)? (b) ph of solution mde from dissoving.1 mol solid NOH into 1. L wter? (c) ph fter dding.1 mol solid NOH into 1. L of the solution ()? () ph=4.74 (b) ph=1. (c) Mjor species before ny rection : CH COOH, N +, CH COO -, OH -, H O ph = = 5. OH - (q) + CH COOH(q) H O(l) + CH COO - (q) before rection.1 mol.5 mol (=.5 M x 1. L).5 mol(=.5 M x 1. L) fter rection mol (=.1-.1).49 mol (=.5-.1).51 mol (=.5+.1) Mjor species in solution : CH COOH, N +, CH COO -, H O CH COOH(q) H + (q) + CH COO - (q) initil eq.49-x x.51+x ph = =. K [ H [ CHCOO [ CH COOH [ H x 1.71 x (5% rule : [ CH COOH ph -log( x(5.1 x) 4.9 x M M 4.9M ) 4.76 x(5.1) 4.9 5%)

6 Buffer Solutions Key Points on Buffer Solutions 1. They re wek cids or bses contining common ion.. After ddition of strong cid or bse, del with stoichiometry first, then equilibrium. Originl buffered solution ph Modified ph Step 1 Do stoichichiometry clcultions to determin new concentrtions. Assume rection with H + /OH - goes to completion. Step Do equlibrium clcultions.

7 Buffer Solutions Buffering: How does it work? Buffer solution contins reltively lrge quntity of wek cid HA (or bse B) nd its conjugte bse A - (cid BH + ). Originl buffer ph (HA nd A - ) HA H + + A - OH - dded Added OH - ions replced by A - ions. (OH - + HA H O + A - rection goes to completion) Finl ph originl ph [ HA [ H buffer K [ A OH - dded [ H [ H buffer [ HA [ OH [ HA [ dded H K K [ A [ OH [ A dded

8 Buffer Solutions Buffering: How does it work? Buffer solution contins reltively lrge quntity of wek cid HA (or bse B) nd its conjugte bse A - (cid BH + ). Originl buffer ph (HA nd A - ) HA H + + A - [ HA [ H buffer K [ A H + dded Added H + ions replced by HA. (H + + A - HA HA:wek cid A - hs high ffinity for H + ) H + dded Finl ph originl ph [ H [ H buffer [ HA [ H [ HA [ dded H K K [ A [ H [ A dded

9 Buffer Solutions Buffering: How does it work? Buffer solution contins reltively lrge quntity of wek cid HA (or bse B) nd its conjugte bse A - (cid BH + ). Originl buffer ph (B nd BH + ) B + H O BH + + OH - H + dded Added H + ions replced by BH +. (H + + B BH + rection goes to completion) Finl ph originl ph [ B [ BH [ OH buffer Kb H + dded [ OH [ OH buffer [ B [ H [ B [ dded OH Kb K b [ BH [ H [ BH dded

10 Buffer Solutions Buffering: How does it work? Buffer solution contins reltively lrge quntity of wek cid HA (or bse B) nd its conjugte bse A - (cid BH + ). Originl buffer ph (B nd BH + ) B + H O BH + + OH - OH - dded Added OH - ions replced by B. (BH + + OH - B + H O OH - hs high ffinity for H + ) Finl ph originl ph [ B [ BH [ OH buffer Kb OH - dded [ OH [ OH buffer [ B [ OH [ B [ dded OH Kb K b [ BH [ OH [ BH dded

11 Buffer Solutions Buffering: How does it work? Originl buffer ph (B nd BH + ) B + H O BH + + OH - [ H buffer Kw [ OH buffer K K [ OH b buffer K [ BH [ B BH + H + + B [ B [ BH [ OH buffer Kb Originl buffer ph (HA nd A - ) HA H + + A - [ HA [ H buffer K [ A log[ H ph [ H buffer buffer buffer K log K pk [ cid [ bse [ cid log( ) [ bse [ bse log( ) [ cid Henderson-Hsselblch eqution ph of buffer solution is determined by the rtio of [wek cid nd [wek bse

12 Buffer Solutions Buffering: How does it work? Ex) ph of solution contining.75 M lctic cid (HC H 5 O, K = 1.4 x 1-4 ) nd.5 M NC H 5 O? Mjor species : HC H 5 O, N +, C H 5 O -, H O HC H 5 O (q) H + (q) + C H 5 O - (q) initil.75.5 eq.75-x x.5+x K (5% rule : [ [ H [ CH5O [ HC H O [ H x HC H x 4.1 ph -log( O 5 4 x(.5 x).75 x 4 M M.75M ).8 x(.5).75 5%) Henderson- Hsselblch eqution ph pk log(1.4 1 [ CH5O log( ) [ HC H O 4 ) log( 5.5 ).75.8

13 Buffer Solutions Buffering: How does it work? Ex) () ph of solution contining.5 M NH (K b = 1.8 x 1-5 ) nd.4 M NH 4 Cl? (b) ph fter dding.1 mol HCl(g) into 1. L of the buffered solution ()? () Mjor species : NH, NH 4+, Cl -, H O K NH 4+ (q) NH (q) + H + (q) K K w b Henderson- Hsselblch eqution ph pk [ NH log( [ NH 4 ).5 1 log(5.61 ) log( ) (b) Mjor species before ny rection : NH, NH 4+, Cl -, H +, H O NH (q) + H + (q) NH 4+ (q) before.5 mol.1 mol.4 mol rection (=1. L x.5m) (=1. L x.4 M) fter.15 mol (=.5-.1).5 (=.4+.1) rection Henderson- Hsselblch eqution ph pk [ NH log( [ NH 4 ).15 1 log(5.61 ) log( )

14 Buffer Solutions Summry of the Most Importnt Chrcteristics of Buffered Solution Buffers contin reltively lrge mounts of wek cid (or bse) nd corresponding bse (or cid). HA nd A - (or B nd BH + ) Added H + rects to completion with the wek bse. H + + A - HA or H + + B BH + Added OH - rects to completion with the wek cid. OH - + HA A - + H O or OH - + BH + B + H O The ph is determined by the rtio of the concentrtions of the wek cid nd wek bse. ph buffer pk [ bse log( ) [ cid

15 Buffer Cpcity Buffer cpcity : the mount of H + or OH - the buffer cn bsorb without significnt chnge in ph. Ex) Clculte the chnge in ph when.1 mol HCl(g) is dded to 1. L of the following solution. Solution A: 5. M CH COOH (K = 1.8 x 1-5 ) nd 5. M NCH COO Solution B:.5 M CH COOH nd.5 M NCH COO Solution A Mjor species before ny rection : CH COOH, N +, CH COO -, H O Mjor species in solution : CH COOH, N +, CH COO -, Cl -, H O ph pk [ CH COO log( ) [ CH COOH 5. 5 log(1.8 1 ) log( ) H + (q) + CH COO - (q) H O(l) + CH COOH(q) before.1 mol 5. mol 5. mol rection ( = 5. M x 1. L) ( = 5. M x 1. L) fter mol 4.99 mol 5.1 mol rection ph pk [ CH COO log( ) [ CH COOH log(1.8 1 ) log( ) ph = = ph of buffered solution is determined by the rtio of [A - /[HA.

16 Buffer Cpcity Buffer cpcity : the mount of H + or OH - the buffer cn bsorb without significnt chnge in ph. Ex) Clculte the chnge in ph when.1 mol HCl(g) is dded to 1. L of the following solution. Solution A: 5. M CH COOH (K = 1.8 x 1-5 ) nd 5. M NCH COO ph = = Solution B:.5 M CH COOH nd.5 M NCH COO Solution B Mjor species before ny rection : CH COOH, N +, CH COO -,H O Mjor species in solution : CH COOH, N +, CH COO -, Cl -, H O ph pk [ CH COO log( ) [ CH COOH.5 5 log(1.8 1 ) log( ) H + (q) + CH COO - (q) H O(l) + CH COOH(q) before.1 mol.5 mol.5 mol rection ( =.5 M x 1. L) ( =.5 M x 1. L) fter mol.4 mol.6 mol rection ph pk [ CH COO log( ) [ CH COOH.4 5 log(1.8 1 ) log( ) ph = =.18 ph of buffered solution is determined by the rtio of [A - /[HA.

17 Buffer Cpcity Buffer cpcity : the mount of H + or OH - the buffer cn bsorb without significnt chnge in ph. Ex) Clculte the chnge in ph when.1 mol HCl(g) is dded to 1. L of the following solution. Solution A: 5. M CH COOH (K = 1.8 x 1-5 ) nd 5. M NCH COO ph = = Solution B:.5 M CH COOH nd.5 M NCH COO ph = =.18 [ A 5. H [ A.996 [ HA 5. dded [ HA % chnge [ A [ HA H + dded [ A [ HA % chnge Buffer cpcity : is determined by the mgnitudes of the [HA nd [A -. ph of buffered solution is determined by the rtio of [A - /[HA.

18 Buffer Cpcity [ Ac [ HAc H + dded [ Ac [ HAc % chnge [ Ac 1. H 1 + [ HAc.1 dded [ Ac [ HAc Optiml buffering occurs when [HA = [A % chnge ph pk [ A log( ) [ HA pk log(1) pk pk of the wek cid to be used in the buffer should be s close s possible to the desired ph. ph of buffered solution is determined by the rtio of [A - /[HA.

19 Buffer Cpcity Ex) Which one is the best to mke ph=4. buffer solution? with wht [HA/[A - rtio? () chlorocetic cid (K = 1.5 x 1 - ) ph 4. [ H M pk log(1.51 ).869 (b) propnoic cid (K = 1. x 1-5 ) [ H K [ HA 5.1 [ A 5 M pk log(1. 1 [ HA [ H [ A K ) [ HA [ H [ A K (c) benzoic cid (K = 6.4 x 1-5 ) pk log( ) 4.19 [ HA [ H [ A K (d) hypochlorous cid (K =.5 x 1-8 ) pk log(.5 1 [ HA [ H [ A K )

20 Titrtions nd ph Curves Titrtion curve (ph curve) : A plot of ph of the solution being nlyzed s function of the mount of titrnt dded Strong Acid-Strong Bse Titrtion H + (q) + OH - (q) H O(l) Ex) Clculte ph of the solution 5. ml of. M HNO when the following mounts of.1 M NOH re dded to the HNO solution. () ml (b) 1. ml (c). ml (d) 5. ml (e) 1 ml (f) 15 ml (g) ml () Mjor species : H +, NO -, H O [H + =. M ph =.699 (b) Mjor species before ny rection : H +, NO -, N +, OH -, H O H + + OH - H O(l) before 1. mmol 1. mmol rection (=5. ml x. M) (=1. ml x.1 M) fter 9. mmol rection (=1.-1.) (=1.-1.) Mjor species fter rection : H +, NO -, N +, H O [ H 9.mmol (5. 1.) ml.15m ph log(.15).8 1 ml x 1 M= 1 mmol

21 Strong Acid-Strong Bse Titrtion Titrtions nd ph Curves Ex) Clculte ph of the solution 5. ml of. M HNO when the following mounts of.1 M NOH re dded to the HNO solution. () ml (b) 1. ml (c). ml (d) 5. ml (e) 1 ml (f) 15 ml (g) ml (c) Mjor species before ny rection : H +, NO -, N +, OH -, H O H + + OH - H O(l) before 1. mmol. mmol rection (=5. ml x. M) (=. ml x.1 M) fter 8. mmol rection (=1.-.) (=.-.) [ H 8.mmol (5..) ml ph log(.11).94.11m Mjor species fter rection : H +, NO -, N +, H O (d) Mjor species before ny rection : H +, NO -, N +, OH -, H O H + + OH - H O(l) before 1. mmol 5. mmol rection (=5. ml x. M) (=5. ml x.1 M) fter 5. mmol rection (=1.-5.) (=5.-5.) [ H 5.mmol (5. 5.) ml ph log(.5) 1..5M Mjor species fter rection : H +, NO -, N +, H O

22 Strong Acid-Strong Bse Titrtion Titrtions nd ph Curves Ex) Clculte ph of the solution 5. ml of. M HNO when the following mounts of.1 M NOH re dded to the HNO solution. () ml (b) 1. ml (c). ml (d) 5. ml (e) 1 ml (f) 15 ml (g) ml (e) Mjor species before ny rection : H +, NO -, N +, OH -, H O H + + OH - H O(l) before 1. mmol 1. mmol rection (=5. ml x. M) (=1 ml x.1 M) fter 1. x 1-7 M 1. x 1-7 M rection Mjor species fter rection : NO -, N +, H O (f) Mjor species before ny rection : H +, NO -, N +, OH -, H O ph 7. H + + OH - H O(l) before 1. mmol 15. mmol rection (=5. ml x. M) (=15 ml x.1 M) fter 5. mmol rection (=1.-1.) (=15.-1.) [ OH 5.mmol (5. 15.) ml.5m poh log(.5) 1.6 ph 14 poh 1.4 Mjor species fter rection : OH -, NO -, N +, H O

23 Strong Acid-Strong Bse Titrtion Titrtions nd ph Curves Ex) Clculte ph of the solution 5. ml of. M HNO when the following mounts of.1 M NOH re dded to the HNO solution. () ml (b) 1. ml (c). ml (d) 5. ml (e) 1 ml (f) 15 ml (g) ml (g) Mjor species before ny rection : H +, NO -, N +, OH -, H O H + + OH - H O(l) before 1. mmol. mmol rection (=5. ml x. M) (= ml x.1 M) fter 1. mmol rection (=1.-1.) (=.-1.) Mjor species fter rection : OH -, NO -, N +, H O [ OH 1.mmol (5. ) ml.4 M poh log(.4) 1.98 ph 14 poh 1.6

24 Strong Acid-Strong Bse Titrtion Titrtions nd ph Curves Ex) Clculte ph of the solution 5. ml of. M HNO when the following mounts of.1 M NOH re dded to the HNO solution. () ml (b) 1. ml (c). ml (d) 5. ml (e) 1 ml (f) 15 ml (g) ml ().699 (b).8 (c).94 (d) 1. (e) 7. (f) 1.4 (g) 1.6 ph Enough titrnt hs been dded to rect exctly with the solution being nlyzed. The ph curve for the titrtion of 1. ml of.5 M NOH with 1. M HCl.

25 Titrtions nd ph Curves Titrtions of Wek Acids with Strong Bses ph New ph Step 1 A stoichiometry problem - rection is ssumed to run to completion - then determine remining species. Step An equilibrium problem - determine position of wek cid equilibrium nd clculte ph.

26 Titrtions of Wek Acids with Strong Bse Titrtions nd ph Curves Ex) Clculte ph of the solution 5. ml of.1 M CH COOH (K = 1.8 x 1-5 ) when the following mounts of.1 M NOH re dded to the CH COOH solution. () ml (b) 1. ml (c) 5. ml (d) 4. ml (e) 5. ml (f) 6. ml (g) 75. ml () Mjor species: CH COOH, H O CH COOH(q) H + (q) + CH COO - (q) initil.1 M 1. x 1-7 M( ) eq.1-x x x K [ H [ CHCOO [ CH COOH [ H x 1.1 x.1 x M x.1 x 1.1 (5% rule :.1.1 ph.89 5%)

27 Titrtions of Wek Acids with Strong Bse Titrtions nd ph Curves Ex) Clculte ph of the solution 5. ml of.1 M CH COOH (K = 1.8 x 1-5 ) when the following mounts of.1 M NOH re dded to the CH COOH solution. () ml (b) 1. ml (c) 5. ml (d) 4. ml (e) 5. ml (f) 6. ml (g) 75. ml (b) Mjor species before ny rection : CH COOH, N +, OH -, H O OH - (q) + CH COOH(q) H O(q) + CH COO - (q) before 1. mmol 5.mmol rection (=1. ml x.1 M) (= 5. ml x.1m) fter 4. mmol 1. mmol rection (=1.-1.) (=5.-4.) [ H Mjor species fter rection : CH COOH, N +, CH COO -, H O CH COOH(q) H + (q) + CH COO - (q) initil (4./6.) M (1./6.) M eq (4./6.-x) M x M (1./6.+x) M K x 7.1 [ H [ CHCOO [ CH COOH 5 M x( x) x x 4. x 7.1 (5% rule : 4. / ph %) K 1.81 [ H ph pk 5 K log(1.8 1 [ CHCOO log( ) [ CH COOH 4.74 log( [ H [ CHCOO [ CH COOH 5 [ CHCOOH [ CH COO ) log( 1 ) x ) x

28 Titrtions of Wek Acids with Strong Bse Titrtions nd ph Curves Ex) Clculte ph of the solution 5. ml of.1 M CH COOH (K = 1.8 x 1-5 ) when the following mounts of.1 M NOH re dded to the CH COOH solution. () ml (b) 1. ml (c) 5. ml (d) 4. ml (e) 5. ml (f) 6. ml (g) 75. ml (c) Mjor species before ny rection : CH COOH, N +, OH -, H O OH - (q) + CH COOH(q) H O(q) + CH COO - (q) before.5 mmol 5.mmol rection (=5. ml x.1 M) (= 5. ml x.1m) fter.5 mmol.5 mmol rection (=.5-.5) (=5.-.5) [ H Mjor species fter rection : CH COOH, N +, CH COO -, H O CH COOH(q) H + (q) + CH COO - (q) initil (.5/75.) M (.5/75.) M eq (.5/75.-x) M x M (.5/75.+x) M K x 1.81 [ H [ CHCOO [ CH COOH 5 M x( x 7.1 (5% rule :.5/ ph 4.74 x) x x 5 5%) ph pk log(1.8 1 [ CH COO log( ) [ CH COOH 5 ) log( 4.74 log(1) mmol (5.5.) ml.5 mmol (5.5.) ml hlfwy point : hlfwy to the equivlence point [HA = [A -, ph = pk )

29 Titrtions of Wek Acids with Strong Bse Titrtions nd ph Curves Ex) Clculte ph of the solution 5. ml of.1 M CH COOH (K = 1.8 x 1-5 ) when the following mounts of.1 M NOH re dded to the CH COOH solution. () ml (b) 1. ml (c) 5. ml (d) 4. ml (e) 5. ml (f) 6. ml (g) 75. ml (d) Mjor species before ny rection : CH COOH, N +, OH -, H O OH - (q) + CH COOH(q) H O(q) + CH COO - (q) before 4. mmol 5.mmol rection (=4. ml x.1 M) (= 5. ml x.1m) fter 1. mmol 4. mmol rection (=4.-4.) (=5.-4.) [ H Mjor species fter rection : CH COOH, N +, CH COO -, H O CH COOH(q) H + (q) + CH COO - (q) initil (1./9.) M (4./9.) M eq (1./9.-x) M x M (4./9.+x) M K x 4.51 [ H [ CHCOO [ CH COOH 6 M x( x 4.51 (5% rule : 1. / ph 5.5 x) 4. x x 6 5%) ph pk log(1.8 1 [ CH COO log( ) [ CH COOH 5 ) log( 4. mmol (5.4.) ml 1. mmol (5.4.) ml 4.74 log( 4) )

30 Titrtions of Wek Acids with Strong Bse Titrtions nd ph Curves Ex) Clculte ph of the solution 5. ml of.1 M CH COOH (K = 1.8 x 1-5 ) when the following mounts of.1 M NOH re dded to the CH COOH solution. () ml (b) 1. ml (c) 5. ml (d) 4. ml (e) 5. ml (f) 6. ml (g) 75. ml (e) Mjor species before ny rection : CH COOH, N +, OH -, H O OH - (q) + CH COOH(q) H O(q) + CH COO - (q) before 5. mmol 5.mmol rection (=5. ml x.1 M) (= 5. ml x.1m) fter mmol 5. mmol rection (=5.-5.) (=5.-5.) Mjor species fter rection : N +, CH COO -, H O CH COO - (q) + H O(l) OH - (q) + CH COOH(q) initil (5./1.) M M M eq (5./1-x) M x M x M Equivlence Point K b K K w [ OH [ OH [ CHCOOH [ CH COO x 5.1 x 5.1 M (5% rule : 5. / ph 14. poh x 6 x 5%) x

31 Titrtions of Wek Acids with Strong Bse Titrtions nd ph Curves Ex) Clculte ph of the solution 5. ml of.1 M CH COOH (K = 1.8 x 1-5 ) when the following mounts of.1 M NOH re dded to the CH COOH solution. () ml (b) 1. ml (c) 5. ml (d) 4. ml (e) 5. ml (f) 6. ml (g) 75. ml (f) Mjor species before ny rection : CH COOH, N +, OH -, H O OH - (q) + CH COOH(q) H O(q) + CH COO - (q) before 6. mmol 5.mmol rection (=6. ml x.1 M) (= 5. ml x.1m) fter 1. mmol 5. mmol rection (=6.-5.) (=5.-5.) Mjor species fter rection : OH -, N +, CH COO -, H O [ OH ph 14. poh (g) Mjor species before ny rection : CH COOH, N +, OH -, H O 1.mmol (5. 6.) ml 14. [ log( OH - (q) + CH COOH(q) H O(q) + CH COO - (q) before rection 7.5 mmol 5.mmol fter rection.5 mmol 5. mmol M ) [ OH.5mmol (5. 75.) ml.1 M ph 1.

32 Titrtions of Wek Acids with Strong Bse Titrtions nd ph Curves Ex) Clculte ph of the solution 5. ml of.1 M CH COOH (K = 1.8 x 1-5 ) when the following mounts of.1 M NOH re dded to the CH COOH solution. () ml (b) 1. ml (c) 5. ml (d) 4. ml (e) 5. ml (f) 6. ml (g) 75. ml ().89 (b) 4.14 (c) 4.74 (d) 5.5 (e) 8.7 (f) (g) 1. ph hlfwy point Equivlence point OH - governs buffering effect Equivlence point

33 Titrtions nd ph Curves Titrtions of Wek Acids with Strong Bse Ex) Clculte ph of the solution 5. ml of.1 M HCN (K = 6. x 1-1 ) when the following mounts of.1 M NOH re dded to the HCN solution. () 8. ml (b) t the hlfwy point (5. ml) (c) t the equivlence point (5. ml) () Mjor species before ny rection : HCN, N +, OH -, H O OH - (q) + HCN(q) H O(q) + CN - (q) before.8 mmol 5. mmol rection (=8. ml x.1 M) (= 5. ml x.1m) fter 4. mmol.8 mmol rection (=.8-.8) (=5.-.8) [ H Mjor species fter rection : HCN, N +, CN -, H O HCN(q) H + (q) + CN - (q) initil (4./58.) M (.8/58.) M eq (4./58.-x) M x M (.8/58.+x) M K 6.1 x [ H [ CN [ HCN M x( x).8 x x 4. x.1 (5% rule : 4. / ph %) ph pk log( 6.1 [ CN log( ) [ HCN 1 ) log( log( ) )

34 Titrtions nd ph Curves Titrtions of Wek Acids with Strong Bse Ex) Clculte ph of the solution 5. ml of.1 M HCN (K = 6. x 1-1 ) when the following mounts of.1 M NOH re dded to the HCN solution. () 8. ml (b) t the hlfwy point (5. ml) (c) t the equivlence point (5. ml) (b) hlfwy point OH - (q) + HCN(q) H O(q) + CN - (q) [ CN fter rection [HCN = [CN - ph pk log( ) pk 9. 1 [ HCN (c) Mjor species before ny rection : HCN, N +, OH -, H O OH - (q) + HCN(q) H O(q) + CN - (q) before rection 5. mmol 5. mmol fter rection 5. mmol Mjor species fter rection : N +, CN -, H O CN - (q) + H O(l) HCN(q) + OH - (q) initil (5./1.) M eq 5./1. - x x x K b K b K K w [ HCN[ OH [ CN x x x [ OH x 8.91 M (5% rule : 5.1 ph 14 poh %)

35 Titrtions nd ph Curves Titrtions of Wek Acids with Strong Bse Ex) Clculte ph of the solution 5. ml of.1 M HCN (K = 6. x 1-1 ) when the following mounts of.1 M NOH re dded to the HCN solution. () 8. ml (b) t the hlfwy point (5. ml) (c) t the equivlence point (5. ml) () 8.49 (b) 9.1 (c) 1.95 ph Ex) Clculte ph of the solution 5. ml of.1 M CH COOH (K = 1.8 x 1-5 ) when the following mounts of.1 M NOH re dded to the CH COOH solution. () ml (b) 1. ml (c) 5. ml (d) 4. ml (e) 5. ml (f) 6. ml (g) 75. ml ().89 (b) 4.14 (c) 4.74 (d) 5.5 (e) 8.7 (f) (g) 1. ph hlfwy point Equivlence point Equivlence point : determined by mount of cid ph t the equivlence point : ffected by the cid strength [A - : stronger bse hlfwy point

36 Titrtions nd ph Curves Titrtions of Wek Acids with Strong Bse Ex) Clculting K. A Solution prepred from. mmol of solid monoprotic cid (HA) in 1. ml is titrted with.5 M NOH. After. ml NOH solution hs been dded, the ph is 6.. K of HA? Mjor species before ny rection : HA, N +, OH -, H O OH - (q) + HA(q) H O(q) + A - (q) before 1. mmol. mmol rection (=. ml x.5 M) fter 1. mmol 1. mmol rection (=1.-1.) (=.-1.) Mjor species fter rection : HA, N +, A -, H O HA - (q) H + (q) + A - (q) initil (1./1.) M M (1./1.) M eq (1./1.-x) M x M (1./1. + x) M K [ H [ A [ HA x( ( [ H x) x) 1 ph 1 x M x 1.1 (5% rule : 1. / Shortcut : hfwy point 6 pk [ HA [ A ph 5%) [ A log( ) [ HA pk

37 Titrtions nd ph Curves Titrtions of Wek Bses with Strong Acids Ex) Clculte ph of the solution 1. ml of.5 M NH when the following mounts of.1 M HCl re dded to the NH solution. () ml (b) 1. ml (c) 5. ml (d) 5. ml (e) 6. ml () Mjor species : NH, H O [ NH NH (q) + H O(l) NH 4+ (q) + OH - 4 [ OH x K (q) b [ NH.5 x initil.5 M x eq.5 -x x x [ OH ph.5 (b,c) Before equivlence point : Mjor species before ny rection : NH, H +, Cl -, H O H + (q) + NH (q) NH 4+ (q) before rection y mmol 5. mmol fter rection 5.-y mmol y mmol Mjor species fter rection : NH, NH 4+, Cl -, H O NH (q) + H O(l) NH 4+ (q) + OH - [ NH 4 [ OH (q) K b [ NH initil w M z M eq w-x z+x x zx [ OH ph w ( z x) x w x

38 Titrtions nd ph Curves Titrtions of Wek Bses with Strong Acids Ex) Clculte ph of the solution 1. ml of.5 M NH when the following mounts of.1 M HCl re dded to the NH solution. () ml (b) 1. ml (c) 5. ml (d) 5. ml (e) 6. ml (d) At the equivlence point: Mjor species before ny rection: NH, H +, Cl -, H O H + (q) + NH (q) NH 4+ (q) before rection 5 mmol 5. mmol fter rection 5 mmol Mjor species fter rection : NH 4+, Cl -, H O NH 4+ (q) NH (q) + H + (q) [ NH[ H K initil w M [ NH4 eq w-x x x [ H ph x w x x w (e) After the equivlence point: Mjor species before ny rection: NH, H +, Cl -, H O H + (q) + NH (q) NH 4+ (q) before rection y mmol 5. mmol fter rection y-5 5 mmol Mjor species fter rection : H +, NH 4+, Cl -, H O [H + => ph

39 Titrtions nd ph Curves Titrtions of Wek Bses with Strong Acids Ex) Clculte ph of the solution 1. ml of.5 M NH when the following mounts of.1 M HCl re dded to the NH solution. () ml (b) 1. ml (c) 5. ml (d) 5. ml (e) 6. ml

40 Determining the equivlence point 1. ph meter -- > titrtion curve Acid-Bse Indictors. Acid-bse indictors : Usully wek cids of which protonted (HIn) nd deprotonted (In - ) forms exhibits different colors. They mrks the end point of titrtion by chnging color. The equivlence point is not necessrily the sme s the end point. phenolphthlein in cidic solution in bsic solution

41 Acid-Bse Indictors Indictor working process HIn(q) H An indictor (HIn) with K =1. x (q) + In - (q) Red Blue HIn OH - OH - K [ In K [ HIn [ H [ H [ In [ HIn Red ph = 1 solution Usully, humn eyes cn detect color chnges when K [ H [ H [ In [ HIn 1K 1.1 [ In K [ HIn [ H 7 [ In [ HIn ph 7 Blue Reddish purple

42 Acid-Bse Indictors Indictor working process HIn(q) H An indictor (HIn) with K =1. x (q) + In - (q) Red Blue HIn H + H + ph = 1 solution Red Usully, humn eyes cn detect color chnges when K [ H [ In [ HIn [ H K [ In K [ HIn [ H 9 [ In [ HIn ph 9 Bluish purple K [ In K [ HIn [ H [ H [ In [ HIn Blue

43 Acid-Bse Indictors Indictor working process cid bse 1 ) 1 1 log( ) [ [ log( pk pk HIn In pk ph cid bse 1 ) 1 1 log( ) [ [ log( pk pk HIn In pk ph Color chnge rnge: 1 pk ph

44 Choice of Indictor strong cid - strong bse titrtion Acid-Bse Indictors wek cid - strong bse titrtion Either one is OK. The ph curve for the titrtion of 5 ml of.1 M CH COOH with.1 M NOH.

45 Solubility Equilibri nd the Solubility Product Chpter 4. K CrO 4 (q) K CrO 4 (q) + B(NO ) (q) K(NO ) + BCrO 4 (s) Solubility ffects out lives lot. Ex) BSO 4 [X-ry gent (B + ): If its solubity is high, we die becuse of toxic B +

46 Solubility Equilibri nd the Solubility Product For solids dissolving to form queous solutions CF (s) C + (q) + F - (q) H O equilibrium expression K [ C [ F [ CF K sp [ C [ F Solubility product constnt (or solubility product) (no unit) => n equilibrium constnt t given temperture Solubility => concentrtion of CF tht dissolves, which equls [C + (or 1/ [F - ). => mens equilibrium position

47 Solubility Equilibri nd the Solubility Product

48 Solubility Equilibri nd the Solubility Product Ex) Bi S hs solubility of 1. x 1-15 M t 5 o C. K sp? Bi S (s) Bi + (q) + S - (q) t eq 1. x 1-15 M x(1. x 1-15 ) M x(1.x1-15 )M K sp = [. x 1-15 x [.x1-15 = 1.1 x 1-7 Ex) K sp of Cu(IO ) is 1.4 x 1-7 t 5 o C. Solubility? Cu(IO ) (s) Cu + (q) + IO - (q) t eq x M x M x M Bi S K sp = x (x) = 1.4 x 1-7 solubility =. x 1 - M

49 Solubility Equilibri nd the Solubility Product Reltive Solubilities AgI(s) K sp = 1.5 x 1-16 CuI(s) K sp = 5. x 1-1 CSO 4 (s) K sp = 6.1 x 1-5 Ksp Slt x M ction x M + nion x M K sp = x x = solubility = K sp AgI(s) K sp = 1.5 x 1-16 CuI(s) K sp = 5. x 1-1 CSO 4 (s) K sp = 6.1 x 1-5 Ksp Solubility K sp Solubility? = x = 4x = 18x 5 Solubility Reltive solubilities cn be predicted by compring K sp vlues only for slts tht produce the sme totl number of ions.

50 Solubility Equilibri nd the Solubility Product Common Ion Effect Ex) K sp of Ag CrO 4 (s) = 9. x 1-1 () solubility in pure wter? (b) solubility in.1 M AgNO solntion () K sp = 4x = 9. x 1-1 solubility = x = 1. x 1-4 M (b) Ag CrO 4 (s) Ag + (q) + CrO 4 - (q) initil.1 M eq.1 + x x K sp = (.1+x) x.1x = 9. x 1-1 solubility = x = 9. x 1-1 M Ag CrO 4 (s) Ag + (q) + CrO - 4 (q).1 M common ion equilibrium

51 Solubility Equilibri nd the Solubility Product ph nd Solubility Mg(OH) (s) Mg + (q) + OH - (q) ph equilibrium solubility ph equilibrium solubility Milk of mgnesi (ntcid) low solubility in stomch (cidic) OH - relesed Ag PO 4 (s) Ag + (q) + PO 4 - (q) ph H + + PO 4 - HPO 4 - equilibrium solubility A slt MX where X - is n effective bse. (HX is wek cid) ph => solubility Ex) Slts contining OH -, S -, CO -, C O 4 -, CrO 4 -..

52 Solubility Equilibri nd the Solubility Product ph nd Solubility limestone CCO (s) C + (q) + CO - (q) + K sp = 8.7 x1-9 CO (g) + H O(l) H CO (q) HCO - (q) + H + (q) equililbrium H + (q) HCO - (q) = > solubility => limestone cve 고수동굴 ( 단양 ) Lury Cvern Mmmoth Cve CO (g) => ph => solubility

53 Precipittion nd Qulittive Anlysis Condition for precipittion Solubility product CF (s) C + (q) + F - (q) H O K sp [ C [ F Q [ C [ F Ion product Q < K sp Q > K sp equlibrium equlibrium Ex) Addition of 75. ml of 4. x 1 - M Ce(NO ) to. ml of. x 1 - M KIO. Will Ce(IO ) (K sp = 1.9 x1-1 ) precipitte? [ Ce [ IO (75.mL)(4.1 M ).861 (75..) ml (.ml)(.1 M ) (75..) ml Q [ Ce [ IO 5.1 Ce(IO ) will precipitte. 1 K sp M M

54 Precipittion nd Qulittive Anlysis Ex) Addition of 1. ml of.5 M Pb(NO ) to. ml of.1 M NI. Will PbI (K sp = 1.4 x1-8 ) precipitte? At eq, [Pb + nd [I -? g of PbI (s)? (1. ml)(.5 M ) [ Pb M.mL (.ml)(.1m ) [ I M.mL Q [ Pb [ I 7.41 PbI will precipitte. 5 K sp PbI (s) Pb + (q) + I - (q) initil.167 M.667 M eq x.167 -x.667-x K sp [ Pb [ I [ Pb [ I numericl solution (.167 x)(.667 x) without considering significn t figures x ( ).51 1?? M M 8 K sp is so smll. Rection goes virtully to completion. Pb + (q) + I - (q) PbI (s) before rxn 5. mmol. mmol fter rxn 1. mmol 5. mmol K sp PbI (s) Pb + (q) + I - (q) initil. M eq x.+x [ Pb [ I [ I x(. x) [ Pb x x..61 mol of PbI 5.mmol.15mmol grm of (.) M 5 ( s) 5.mmol 1.1 PbI mmol ( s) mol molr mss x 1.41 M M.mL 8

55 Precipittion nd Qulittive Anlysis Selective Precipittion NCl Ex) A solution contins [Cu + = 1.4 x 1-4 M nd [Pb + =. x 1 - M. When I - is dded, will PbI (K sp = 1.4 x 1-8 ) or CuI (K sp = 5. x 1-1 ) precipitte first? PbI will precipitte when Q sp [ Pb [ I K sp B + Ag + AgCl(s) Selective Precipittion [ I CuI will precipitte when [ I K [ Pb Q K [ Cu sp sp [ Cu sp [ I K sp M M K sp constrols it. CuI will precipitte first. Seprtion of metl ions

56 Precipittion nd Qulittive Anlysis Selective Precipittion Sulfide ion (S - ) is often used to seprte metl ions. K sp big difference K sp 's re too smll to mke only these preciptte. Other dvntge of using S - : esy to control its concentrtion by using ph. H S H + + HS - K 1 = 1. x 1-7 HS - H + + S - K 1-19 low ph : equlibrium, low concentrtion of [S - high ph : equlibrium, [S -

57 Precipittion nd Qulittive Anlysis Qulittive Anlysis K + N +

58 Equilibri Involving Complex Ions Complex Ion: A chrged species consisting of metl ion surrounded by lignds (Lewis bses). Coordintion Number: Number of lignds ttched to metl ion. (Most common re 6 nd 4.) L 4 Co(H O) 6 + L L Cu(NH 1 ) + 4 L Co(NH ) 6 + Formtion (Stbility) Constnts: The equilibrium constnts chrcterizing the stepwise ddition of lignds to metl ions. Ag + + NH Ag(NH ) + K 1 =.1 x 1 Ag(NH ) + + NH Ag(NH ) + K = 8. x 1

59 Equilibri Involving Complex Ions Ex) Mixing 1. ml of. M NH solution nd 1. ml of 1. x 1 - M AgNO solution. [Ag +, [Ag(NH ) +, nd [Ag(NH ) + t eq? Mjor species before ny rection : NH, Ag +, NO -, H O [NH = 1. M, [Ag + = 5. x 1-4 M NH (q) + H O(l) NH 4+ (q) + OH - (q) K b = 1.8 x 1-5 K b is smll enough not much to chnge [NH. Ag + + NH Ag(NH ) + K 1 =.1 x 1 Ag(NH ) + + NH Ag(NH ) + K = 8. x 1 Both K 1 nd K re big nd NH is lrge excess. => K 1 nd K rections cn be ssumed to go to completion. Ag + + NH Ag(NH ) + before rxn 5. x 1-4 M 1. M fter rxn 1. M 5. x 1-4 M ( x 1-4 )M Ag(NH ) + + NH Ag(NH ) + before eq 1. M 5. x 1-4 M fter eq x 1. +x 5. x 1-4 -x K [ Ag( NH) 8.1 [ Ag( NH ) [ NH 4 [ Ag( NH) 5.1 x 5.1 [ Ag( NH ) [ NH x(1. x) x(1.) K 1.11 [ Ag( NH ) [ Ag 6.11 M 8 M Ag + + NH Ag(NH ) + 8 [ Ag( NH) 6.11 [ Ag [ NH [ Ag (1.)

60 Equilibri Involving Complex Ions Complex Ions nd Solubility How cn we seprte these? AgCl(s) Ag + (q) + Cl - (q) K sp = 1.6 x 1-1 Ag + + NH Ag(NH ) + K 1 =.1 x 1 Ag(NH ) + + NH Ag(NH ) + K = 8. x 1 Adding excess mount of NH will shift equilibrium to left. => dissolving AgCl(s) Solubility of AgCl(s) = [Ag totl dissolved = [Ag + + [Ag(NH ) + + [Ag(NH ) + = [Cl -

61 Equilibri Involving Complex Ions Complex Ions nd Solubility Ex) Solubility of AgCl(s) in 1 M NH solution? AgCl(s) Ag + (q) + Cl - (q) K sp = 1.6 x 1-1 Ag + + NH Ag(NH ) + K 1 =.1 x 1 Ag(NH ) + + NH Ag(NH ) + K = 8. x 1 AgCl(s) + NH (q) Ag(NH ) + (q) + Cl - (q) K K sp K [ Ag( NH) [ Cl 1 K.81 [ NH AgCl(s) + NH (q) Ag(NH ) + (q) + Cl - (q) initil 1. M eq 1-x x x Ag + + NH Ag(NH ) + K 1 x K = 1.7 x 1 7 K 1 1 [ Ag( NH) [ Ag [ NH K K 1 [ Ag( NH) [ Ag [ NH K K, K [ Ag( NH [ Ag [ NH ) ) [ Ag( NH [ Ag( NH ) [ NH ) [ Ag( NH [ Ag( NH ) [ NH K.81 [ Ag( NH) [ Cl [ NH x (1. x) x x [ Cl x.48m solubility of AgCl(s) Ex) Solubility of AgCl(s) in pure wter? [ Cl K sp M

62 Equilibri Involving Complex Ions Two strtegies for dissolving wter-insoluble ioinc solid A slt MX where X - is n effective bse. (HX is wek cid) ph => solubility CCO (s) C + (q) + CO - (q) + H + (q) HCO - (q) A slt MX where X - is not sufficiently bsic. Dissolve it in solution contining lignd tht forms stble complex ions with its ction AgCl(s) + NH (q) Ag(NH ) + (q) + Cl - (q) NH (q) AgCl(s)

63 Equilibri Involving Complex Ions Complex Ions nd Solubility Other methods to dissolve insoluble ionic solids Combintion of rections HgS (K sp = 1-54 ) HCl HNO Hg + + Cl - S - + H + Hg n Cl m H S Temperture Use temperture dependent solubility difference.

64 Using Equilibrium They We Do