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3600_Ch15_probs

# 3600_Ch15_probs - 15-1 15-4 15-7 15-9(a AgCl(s e" Ag(s...

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Unformatted text preview: 15-1. 15-4. 15-7. 15-9. (a) AgCl(s) + e" # Ag(s) + Cl" Hg2C12(s) + 2e" # 2Hg(l) + 2Cl’ (b) E 2 EL — E_= 0.241 — 0.197 = 0.044V For the saturated Ag-AgCl electrode we can write : E = E° — 0.059 16 log ﬁla— Putting in E = 0.197 and E = 0.222 V gives 521C1— = 2.65. For the S.C.E. we can write E = E ~ 0.0591610gﬂlc1— : 0.268 V — 0.059 16 log 2.65 = 0.243 V. A silver electrode serves as an indicator for Ag+ by virtue of the equilibrium Ag+ + e‘ # Ag(s) that occurs at its surface. If the solution is saturated with silver halide, then [Ag+] is affected by changes in halide concentration. Therefore the electrode is also an indicator for halide. (a) From 0 to 50 mL, AgI is precipitating. Between 50 and 100 mL, AgCl is precipitating. At V = 25 mL, _ 1 50.0 [I] = (2—) (0.100 M) = 0.0333M fraction dilution remaining factor [Ag+] = [CI/[1"] = K1/0.033 3 (b) AtV = 75.0 mL, [or] = (0.100 M) (IS—205%) = 0.0200M [Ag+] = [ﬁg/0.0200 (c) E = E. — E_ E = {0.799—0.05916log[ 1 Ag+l } — (0.241), since the right half-cell reaction can be written Ag+ + e' x——‘ Ag(s) K1 0.033 3 At 75.0 mL: E = 0.558 + 0.05916log ————O.§2C(1) 0 ((1) At 25.0mL: E = 0.558 + 0.059 l6log Subtracting gives AE = 0.388 = 0.05916 iogw K91 __.. _ 6 K1/0.O333 2” K1 “ 22X 10 15-21. 15-24. 15-25. ISHIH. [Ft-3:1. IS-EI-S. Uncertainty in pH of standard buffers, junction potential, junction potential drift, sodium or acid errors at extreme pH values, equilibration time, hydration of glass, and temperature of measurement and calibration. If the alkaline solution has a high concentration of Na+ (as in NaOH), the Na+ cation competes with H+ for cation exchange sites on the glass surface. The glass responds as if H+ were present, and the apparent pH is lower than the actual pH. The junction potential changes from ~6.4 mV to —-0.2 mV. A change of 6.4 — 0.2 = +6.2 mV appears to be a pH change of +6.2/59.l6 = +0.10 pH units. .I'tnniyte inn migrates aernss :1 seleetively permeable rnemhrmte them a regien et' high eeneengstjen get err": at law eeneentrtttien. Ien reign-then eentes a charge hniltiup that eppeses furl her inn rnigratlen. '1'he eleetrie peter-rial difference between the twe sides ef the membrane tells us Hie relative eeneentrmiens tit :mttlyte rm each side, acne-[ding tn Frltinlirin 15—2. The specific lean enneentreliun inside tilt“ eleetrisle is ﬁxed. se the eieetrtitie [sweetie] tells us the eeneentnninn el' Ill-I: speeit'ie ian ran the nutside {in the amtlyte selulien }. Ft eerrip-trunri eieetrede eenteins a seeend eherrlieally' active mEJIIhttt-tte etttti-tle the inn-selective membrane- The seeenrl membrane may he mltﬂpetmeable and only HIIriw the sfeeies et' interest te pass threttgh. Allemaﬂ'vely. the Heenttd membrane may etmluiu a snhstnnee (sueh es an enzyme] that resets with enelyte te generate the queries tn whieh the inn seleetltre membrane resj-sinels. P. muhi]: muleenle rlissttlt'esl in the memlnnne liquid phase binds tightly DEI- the len et' interest and weakly te interfering lens. E1 .- eenstnnt +ﬂ¥ ll? H: = L'IUI'Ililt'll'll sun? “5 lugllJiilil-t-t I'Eil'I-l'] new is __l_.|_1_lﬂs_|t}"l t 2 1UEllilieclﬂii “1 _ 'ﬂ'mmv eg_[1-Liti s [Lt-1] ﬁll:- = 1'51- Ill-:1;- _' lF- ll’rtnirlnnen — l-m “112'. F'I'IL = 5.35 :-t HJ'E' M lemming“: —- int-nthth -- H.059 lﬁ lugi [5.213 2-: EH5] hlﬁjxhﬂnl '—' Ettrll-iti'lillt ' .[I'inxl'llllu = lull-"1'11. — [Shun-ian-g = l] n V . F' . _I.'f|.ti5'€| Ih Itlﬁ J =:- “1 ll-‘uuhnm = l-ll :a: lL'I'F’ M ='|'i.'l| l rrigt'l. ...
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