[ ] CEE October 2010 FIRST EXAM. Closed book, one page of notes allowed.

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1 CEE Octber 0 IRST EXAM Clsed bk, ne page f ntes alled. Anser all questins. Please state any additinal assumptins yu made, and sh all rk. Yu are elcme t use a graphical methd f slutin if it is apprpriate. Miscellaneus Infrmatin: R cal/mle J/mle Abslute zer C 1 jule 0.39 calries 540 calries 1 Big Mac 1. (50%) What is the p f a -.00 M slutin f Sdium fluride (Na)? Calculate this fr each f the three cnditins bel (bviusly, the inic strength ill never be zer fr this slutin, but let s assume the ideal case fr part a and b anyay). a. 5 C, I 0 b. 0 C, I 0 c. 5 C, I 0.5 Preferred Apprach recgnize that this is a simple base prblem then adpt an apprpriate set f assumptins, and slve fr [] finally crrect pa (and p ) fr temperature, inic strength, and repeat check assumptins a. 5 C, I 0 Assume a eak base: [ - ] >> [] [ O ] bc if the p a fr / (at 5 C and I0) is 3., then the p b is r [ O ] 4.5x [ O ]

2 p 7.61 Check Assumptins: [ - ] >> [] r: [ ] a [ ] [ ] a [ ] [ ][ ] [ ] >> 1, YES!!! b. 0 C, I 0 determine enthalpy change fr the dissciatin reactin: - then re-estimate a ν i f ( 77.3).9cal / mle lg lg lg ( T T ) 1.303RTT1.9cal / mle lg ( ) 3 ( x cal / mle) ( 98.15) x -4 D the same fr

3 ν i O f 13.36cal / mle O ( ) then re-estimate lg lg lg ( T T ) 1.303RTT cal / mle lg ( ) 3 ( x cal / mle) ( 98.15) x -13 and n: As befre, assume a eak base: [ - ] >> [] [ O ] bc if the p a fr / (at 0 C and I0) is 3.63, then the p b is r [ O ] 6.36x [ O ] p 6.84 Check Assumptins: [ - ] >> [] r: a [ ] [ ][ ] [ ] >> 1

4 [ ] a [ ] [ ] , YES!!! If yu had nt adjusted fr the higher temperature, yu uld have calcuated that p7.8. c. 5 C, I 0.5 determine activity cefficients fr the species in the reactin: - And fr O O - r this level, use the simple Davies equatin fr the charged species, and assume n change in the activity f theuncharged species: lg I f 0.5 ( z) 0. I 1 I lg f lg f lg f f O s: f f 0.7 O () 1 0.( 0.5) then re-estimate a and under this cnditin, i.e., the cnditinal s C a a x x.9 and:

5 C x x 13.7 O O and n: As befre, assume a eak base: [ - ] >> [] [ O ] bc if the p a fr / (at 5 C and I0.5) is.9, then the p b is r [ O ] 4.x [ O ] n e must recgnize that p is related t prtn activity nt cncentratin 7.34 { } lg( f [ ]) lg( 0.7 ) p lg x p 7.48 Check Assumptins: [ - ] >> [] r: c [ ] a [ ] [ ] c a [ ] [ ][ ] [ ] >> 1, YES!!!

6 . (40%) What is the cmplete cmpsitin f a 1-liter vlume f ater cntaining - M f ammnium bisulfide (N 4 S)? Apprximate values (± 0. lg units) ill suffice. Apprach prepare a lgc vs p diagram fr ammnia system (C T 0.01 M) and the acetic acid system (C T 0.01M) superimpsed ver it. rite the PBE and find a slutin read ff cncentratins frm the graph This is a gd prblem fr the graphical slutin (n acid/base cnjugates added, nr any strng acids r bases). The first task is then t prepare the species lines n ur usual lg C vs p axes (see bel) Recall that e re adding ammnium catin (N 4 ) and the partially deprtnated bisulfide (S - ). These are simple slutins f t unrelated acids/bases. Therefre e dn t have any acid/cnjugate base mixtures, nr d e have an acids r bases that have been partly titrated ith a strng acid r base. This means e are free t use the PBE, and in fact, shuld use the PBE (an ENE n t give us a clean r identifiable intersectin). Thus, the PBE is: [ S] [ ] [O - ] [N 3 ] [S - ] And if e presume that and O- are insignificant, e get: [ S] [N 3 ] [S - ] And ging a step further e might presume that the sulfide is small as ell. This gives us the PBE intersectin [ S] [N 3 ]

7 O - N 4 - S - N Lg C -7-8 S -9 - S p p 8.15 [ ] 7.1 x -9 lg [ S] [ S] 7.0 x -4 lg [S - ] -.0 [S - ] 1 x - lg [S - ] -7.8 [S - ] x -8 lg [N 4 ] -.0 [N 4 ] 1 x - lg [N 3 ] -3.1 [N 3 ] 8 x -4 lg [O - ] [O - ] 1.4 x -6 Check assumptins: [ S] >> [ ] >> -8.15, YES [N 3 ] >> [O - ] -3.1 >> -5.85, again YES

8 3. (%) True/alse. Mark each ne f the flling statements ith either a "T" r an "". a. T Water is an amphteric substance. b. A nan gram is equivalent t ne-thusanths f a milligram. c. T The third mst cmmn gas in the atmsphere is argn d. T Nn-carbnate hardness nly exists in aters ith alkalinities less than than their ttal hardness. e. T Mass defects are directly prprtinal t nuclear binding energy f. T g. h. i. T The Guntelberg Apprximatin says that activity cefficients are dependent n charge and inic strength, but nt n in size. The reactivity f neutral species is unaffected by changes in inic strength. Increases in inic strength cause a increase in the pa f an acid, if the fully-prtnated frm f the acid is an uncharged species. The standard assumptin used fr calculating the p f buffer slutins is that [] and [O-] are negligible. j. T The value f α plus α 1 must alays equal unity fr a mnprtic acid.

9 Selected Acidity Cnstants (Aqueus Slutin, 5 C, I 0) NAME ORMULA pa Perchlric acid ClO4 ClO STRONG ydrchlric acid Cl Cl - -3 Sulfuric acid SO4 SO (&) ACIDS Nitric acid NO3 NO ydrnium in 3O O 0 Trichlracetic acid CCl3COO CCl3COO Idic acid IO3 IO3-0.8 Bisulfate in SO4 - SO4 - Phsphric acid 3PO4 PO (&7.,1.3) -Phthalic acid C64(COO) C64(COO)COO-.89 (&5.51) Citric acid C35O(COO)3 C35O(COO)COO (&4.77,6.4) ydrfluric acid - 3. Aspartic acid C6N(COO) C6N(COO)COO (&9.8) m-ydrxybenzic acid C64(O)COO C64(O)COO (&9.9) p-ydrxybenzic acid C64(O)COO C64(O)COO (&9.3) Nitrus acid NO NO Acetic acid C3COO C3COO Prpinic acid C5COO C5COO Carbnic acid CO3 CO (&.33) ydrgen sulfide S S (&13.9) Dihydrgen phsphate PO4 - PO4-7. ypchlrus acid OCl OCl Bric acid B(O)3 O B(O)4-9. (&1.7,13.8) Ammnium in N4 N3 9.4 ydrcyanic acid CN CN p-ydrxybenzic acid C64(O)COO - C64(O)COO- 9.3 Phenl C65O C65O m-ydrxybenzic acid C64(O)COO - C64(O)COO- 9.9 Bicarbnate in CO3 - CO Mnhydrgen PO4 - PO phsphate Bisulfide in S - S Water O O Ammnia N3 N - 3 Methane C4 C3-34

10 Species f kcal/mle G f kcal/mle Ca (aq) CaC0 3 (s), calcite CaO (s) C(s), graphite 0 0 CO (g) CO (aq) C 4 (g) CO 3 (aq) CO - 3 (aq) CO - 3 (aq) C 3 COO -, acetate (aq) 0 0 (g) 0 0 (aq) (aq) e (aq) e 3 (aq) e(o) 3 (s) NO - 3 (aq) N 3 (g) N 3 (aq) N 4 (aq) NO 3 (aq) O (aq) O (g) 0 0 O - (aq) O (g) O (l) PO -3 4 (aq) PO - 4 (aq) PO - 4 (aq) PO 4 (aq) SO 4 - S - (aq) S(g) S(aq)

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