Chapter 16. Applications of neutralization titrations.

Chapter 16. Applications of neutralization titrations.

Reagents for Neutralization Reactions strong acid or base : eq. point에서명확한 ph 변화有 standard soln. 제조 (acid) 묽은용액의경우매우안정 (HCl) 0.1N HCl 1 hr 동안 boiling로해도농도의 loss 0.5N HCl 10 min 동안 boiling로해도농도의 loss HClO4, H2SO4 사용. HNO3 산화성으로인해不用 1 dilution base로 standardization 2 less frequently careful density measurement 3 by distillation of the concentrated reagent ; (constant boiling HCl) 대기압에따라농도변화 acid 1 eq. 을갖는 distillate의공기중의무게 g constant boiling HCl ------------------- = 164.673 + 0.02039 P equivalent (P : 670 ~ 780 mmhg)

Standardization of acids 1) sodium carbonate ; purified sodium hydrogen carbonate 을 270~ 300 에서 1hr 동안加열. 2NaHCO 3 Na 2 CO 3 + H 2 O + CO 2 (g) 2 step 으로처리. 1 step ; ph 8.4 부근 2 step ; ph 4.0 부근 always used for standardization (ph 변화크기때문 ) BCG, methyl orange H 2 CO 3 CO 2 (g) + H 2 O ; HCO 3-, CO 2-3 의 buffer 파괴 boiling * 적정시용액 boiling CO 2 제거

Other primary standards for acids. 1Tris-(hydroxymethyl)aminomethane(HOCH 3 ) 3 CNH 2 TRIS or HAM. 2 sodium tetraborate 3 mercury(Ⅱ)oxide 4 calcium oxide. preparation of standard solutions of base NaOH ; (or KOH, Ba(OH) 2 ) the soln must be standardized. * glass, atmosphere 에장기간접촉치않는한안정. NaOH + glass silicate 形成 보관 : polyethylene bottle or glass bottle that has been coated with paraffin.

Effect of CO 2 upon standard base solns. Na, K, Ba 의수산화물 atmospheric CO 2 와 avidly react CO 2 + 2OH - CO 3 2- + H 2 O base 의 standardized soln 에의한 CO2 의흡수는그것의 acid titer 를반드시변화시키지는않는다. CO 2 + 2H 3 O + H 2 CO 3 + 2H 2 O CO 3 형성에사용된 acid 의양과同一한 base 량 no error basic transition indicator 사용 (pp) 이때 H3O+ 1 개가사용 CO 3 2- + H 3 O+ HCO 3- + H 2 O base 의 effective normality 감소 Carbonate error 유발 Ba(OH) 2 사용하면 CO 2 흡수하여 ppt 생성 CO 2 + Ba 2+ 2OH - + BaCO 3 (s) + H 2 O Carbonate error 용액제조에사용된고체 reagent 가대기중의 CO 2 흡수 carbonate 상당량존재

* carbonate free OH- soln 제조법 1 Ba(OH) 2 의경우 ; BaCl 2 or BaNO 3 등첨가 sparingly soluble carbonate 감소 KOH, NaOH 의경우, Ba salt 사용 약점有 2 NaOH 용액 ; 50% aqueous soln 제조 Na 2 CO 3 의 very low solubility 利用. supernatant liquid decant 하여희석후사용 위용액제조시증류수묽어서식힌후사용 Arrangement for the storage of standard base solutions. CO 2 흡착제 : soda lime, or astroite 적정중의 CO 2 흡수 : beaker, test tube 로뚜껑 standard soln : 1 주일內사용할경우 polythylene botte 에마개를사용하며可能 buret teflon stopcock 사용이좋다.

Standardization of bases. Weak organic acids 사용 1 Potassium hydrogen phthalate KHC 8 H 4 O 4 장점 : high equivalent 를갖는 nonhygroscopic crystalline solid. 2 Other acid : solubility in water is limited ethanol 에녹임 3 potassium hydrogen iodate, KH(IO 3 ) 2 : high equivalent weight strong acid Typical Applications of Neutralization Titrations, inorganic, organic, biological species ( 산, 염기의속성을갖는 ) 중화적정에서 2 type 의 end point 결정법. 1 indicator 2 ph meter

Elemental analysis Carbon, nitrogen, chlorine, brine, sulfur, phosphorus & fluorine inorganic acid or base 로 convert 시켜적정 Nitrogen ; proteins, synthetic drugs, fertilizers uplosine, portable water supplies organic N 정량 1 Dumas method : virtually all organic N compound 에적용 powdered copper(Ⅱ) oxide 와 sample mixing combustion tube 에서 igniting (sample CO 2, H 2 O, N 2, nitrogen oxides) hot Cu 을통과 N 2 로변화 ignition products CO 2 stream 에의해 Swept(highly concentrated KOH 용액이들어있는분량으로 CO 2, H 2 O, SO 2, HX 흡수 N 2 는흡수치않음 buret 으로부터부분적으로 liquid 를치환 volume 측정

2 Kjeldahl method (1883) protein N2 in grains, meats & other biological materials. sample hot, conc - H 2 SO 4 로산화 excess of strong base로처리 C CO 2, H 2 H 2 O로산화 bound N 2 NH + 4 로 convert *N 2 가 amine or amide 등의 proteineous matter이면정량적으로 NH 4+ 로변화可 *N 2 가 nitro, ago & azoxy group이면 elemental state or nitrogen oxide로 convert. 이런경우, low results reducing agent로 sample 전처리要 ex) salicylic acid, sodium thiosulfate adding certain aromatic heterocyclic compounds (pyridine, its derivatives) resistant to complete oxidation by H 2 SO 4 oxidation process an hour, on more maybe needed.

* Gunning method neutral salt(k 2 SO 4 ) 加 b.p 상승 (H 2 SO 4 ) 주의 ) ig salt concentration 大 NH 4 + ion oxidation * perchloric acid, potassium pernanganate. hydrogen peroxide 의경우 NH 4 + ion 이부분적으로 NO 2 로산화하므로 fail. 1 oxidation step 촉매 ; Hg, Cu, selenium Kjeldahl flask : oxidation distillation after oxidation cooling dilution with H 2 O basic NH + 4 + OH - NH 3 (g) + H 2 O

Chapter 17. Complex formation titrations (complexometic methods) M + + electron pair donor complex ion, coordination conp. ligand( 최소 1 pair의 unshared eleclron 존재 ) ex) H 2 O, NH 3, Cl - coordination number : 배위권에서중심원자와결합하고있는주게원자의수. ex) 6, 4, 2 배위물 Posituve : Cu(NH) 2+ 4 negative : CuCl 2-4 noutral : Cu(NH 2 CH 2 COO) 2 chelates ; is produced when a metal ion coordinates with two donar groups of a single ligand. 여러자리 ligand bidentate, terdentate, Qwadri-, quinque, sexadentate 1) 4 자리배위금속이온 M + quadridentate ligand D 와반응 [MD] M + D MD Kf = ------- = formation constant. [M][D]

2) M + bidentate B M + 2B MB 2 two step [MB] M + B MB K1 =------------- [M][B] [MB 2 ] MB + B MB2 K2 = --------------- [MB][B] [MB] [MB 2 ] [MB 2 ] β2 = K1K2 = ----------- x---------= --------- [M][B] [MB][B] [M][B] 2 3) M + unidentate A M + 4A MA 4, K1, K2, K3, K4 有 fig 11-1 참조. complex formation titrations Curve A ; single step Curve B ; MB 2 two step. K1 = 10 12, K2 = 10 8 Curve C ; MB 4. K1 = 10 8, K2 = 10 6, K3 = 10 4, K4 = 10 2 polydentate ligand + unidentate 보다적정에有利

Titrations with ionrganic complexing reagents. Hg(Ⅱ) 로 I - ion 정량법 11834 年 ) was reported.

titrations with aminepolycarboxyic acids. carboxyic acid groups를갖는 tertiary amines stable chelates를 form. Schwargenbach in 1945 분석시약으로서위치인식 [EDTA (ethylenediaminetetraacetie acid) 에의한 M 정량 ] K1 = 1.0 x 10-2, K2 = 2.1 x 10-3, K3 = 6.9 x 10-7, K4 = 5.5 x 10-11 有用 sexadentate ligand. ab, H 4 Y, H 3 Y -, H 2 Y 2-, HY 3-, Y 4- H 4 Y, NaH 2 Y 2H 2 O are abailable in reagent quality. 130~145 에서 80 에서 drying (50% 상대습도中, for several days) drying(base에서 )

composition of EDTA soln, as a function of ph. relative amount each species in a giren soln ph 에의존 α value plotting 이有 FIg. ph vs EDTA의 α value H 2 Y -2 : prodominent species in ph 3~6 HY 3- ; ph 6~10, Y 4- ; ph 10 이상

complexes of EDTA and Metal lons EDTA 장점 : 1:1 complex 형성.(cation 의 charge 에무관 ) (ph 3~6 에서 )

M + + H 2 Y 2- MHY 2- + H + M +2 + H 2 Y 2- MY 2- + 2H + M 3+ + H 2 Y 2- MY - + 2H + M 4+ + H 2 Y 2- MY + 2H + great stabe in moderately basic solns neutral M 3+ + HY 3- MY (3+4)+ + H + Formation constants for EDTA complexes. [xmy (3+4)+ ] M n+ + Y 4- MY (3+4)+ KMY = ---------- [Mn+][Y 4- ]

derivation of EDTA titration curves. effect of ph. calcium. Mg alkaline medium Zn, Ni moderataly acid solus. EDTA bnffer soln 에서行해야한다. [Y4-] α4 = ------- G G : uncomplexed EDTA 의 total com.

G = [Y 4- ] + [HY 3- ] + [H 2 Y 2- ] + [H 3 Y 2- ] + [H 4 Y] K1 K2 K3 K4 α4 =------------------------------------------------ [H + ]4 + K1[H + ] 3 + K1 K2 [H + ] 2 + K1 K2 K3 [H + ] + K1K2K3K4

Values for α4 EDTA α4 G = [Y 4- ] 를 M n+ + Y 4- MY(n -4 )+ 에代入 [MY(n -4 ) + ] K MY = α4 KMY = ----------------- [M n+ ]G K' MY = conditional or effective formation constant. α4 가적용가능한 ph에서의평행상수

ex) Derive a curve for the titration ; 50.0 ml of 0.01F Ca 2+ + 0.0100F EDTA ph:10 으로 buffering. 1) calculation of conditional constant ; K'CaY = α4 KCaY = (3.5 x 10-1 )(5.0 x 1010) = 1.75 x 1010 2) preequivalence point values for pca. [Ca 2+ ] = the untitrated excess of the ion + dissociation of the complex [=G] after 25 ml加. G uncomplexed Ca +1 ion 의농도 50.0 x 0.0100-25.0 x 0.0100 [Ca 2+ ]= ------------------------- + G 3.33 x 10-3 75.0 무시 pca = -log 3.33 x 10-3 = 2.48

3) equivalence point pca ; 0.00500F in CaY 2- [Ca 2+ ] CaY 2- 의해리에의한것뿐 [Ca 2+ ] = G [CaY 2- ] = 0.00500 - [Ca 2+ ] 0.00500 ne conditional formation constant for CaY 2- at ph10. [CaY 2- ] -------------------- = 1.75 x 1010 [Ca 2+ ] G 0.00500 ---------------------- = 1.75 x 1010 [Ca 2+ ] 2 [Ca 2+ ] = 5.35 x 10-7 pca = 6.27

4) postequivalence point pca CaY 2- 의당량점에서의농도 + EDTA(excess) 60.0 ml加 ; 50.0 x 0.0100 FCaY 2- = -------------------- = 4.55 x 10-3 110 10.0 x 0.0100 FEDTA =------------------ = 9.1 x 10-4 110 [CaY 2- ] = 4.55 x 10-3 - [Ca 2+ ] 4.55 x 10-3 G = 9.1 x 10-4 + [Ca 2+ ] 9.1 x 10-4 4.55 x 10-3 -------------------= 1.75 x 1010 = K'CaY [Ca 2+ ] x 9.1 x 10-4 [Ca 2+ ] = 2.86 x 10-10 pca = 9.54 fig 5. ph 6 에서적정곡선 K 값大 적정곡선 pm jump 大

Effect of Other Complexing Agents on EDTA Titrations. 금속에따라 required ph 에서 basic oxide or hydroxide 로침전생성可 complicate. 이것을하기위해 (to leep the metal ion in soln) auxiliary complexing agent 要 ex) Zn(Ⅱ) 적정 (NH 3 - NH 4 Cl buffer 要 ) NH 3 Zn(Ⅱ) 과 soluble ammire complexes ppt 예방 Zn(NH 3 ) 4 2+ + HY 3- ZnY 2- + 3NH 3 +NH 4+ ph 뿐아니라 NH 3 의 concentration 에의해서도좌우. [Zn 2+ ] Zinc titration 에서 β = ----------------- CZn βzn 을 conditional constant 에代入 [ZnY 2- ] K 7 = α 4 βkzny = ---------------- CznG NH 3 농도의영향 ph9. 참조, 일정 ph 에서착물시약농도에서특징적.

end points for EDTA titrations (metal ion inidcators) : orgaric dyes that form colored chelates with metal ions in a pm range. ( 성질 ) 1 dyes 자신이금속이온과반응 금속 chelate 생성능력有 2 indicator 와금속이온이만든금속킬레이트의안정도상수보다 EDTA 의금속킬레이트의안정도상수가大 3 특이하고강한정색 (1/10 배차이 ) ex) E.B.T(enrcchrome black.t.) in acidic & modorately basic soln. H 2 In - HIn 2- + H + red blue 강한염기성 HIn 2- In 3- 로해리 (orange) end point reaction MIn - + HY 3- HIn 2- + MY 2- red blue (Mg2+ 를 EDTA 로정량時 ) Mg 2+ + HIn 2- MgIn - + H + K = 2.75 x 10-5 blue red

ph 10에서 적색 [MgIn - ][H + ] [MgIn - ] 2.75 x 10-5 = ------------- 2.75 x 105 = -------------- [Mg 2+ ][HIn 2- ] [Mg 2+ ][HIn 2- ] 청색만약 pmg가 4.44 이하 청색? pmg가 6.44 이상 적색 ph 7~11에서 Ca, Mg, Zn, Cd, Hg 2+, Pb +, Mn 2+ 변색방해물 : Cu, Co, Ni, Fe KCN으로 mashing 단점 : 방치하면천천히 decompose 보완 Calmagite. ( 기타시약 ) P.V (pyrocatechol violet) aqueon soln yellow. strongly acidic red basic soln red - violet ph 2~3에서. Bi( 청 ), Th( 적 ) ph 5~6에서. Cu( 청 ) 염기성에서. Ni, Co, Mn, Mg, Zn, Cd, Cu( 청록 ) (Xylenol orange) (PAN)

titration methods employing EDTA. 1 Direct Titration : 25 metal 검출 : 1 ndicator, 전류적정, 전압적정 ( 보조 chelate 加, 완충용액要 ) 2 Bach titration 적정 ph 에서도 reaction rate 小, or EDTA 加 변색이생기지않을경우 (EBT, Calmagite 많이利用 ) 정량금속이온과반응하는 anion 의존재시 방법 : excess EDTA 加 ph 조절 excess EDTA 를 ZnSO 4, Th(NO 3 ) 4, MgSO 4 등의 metal standard soln 으로액적정.

3 Displacement titration. Mn + 용액에 EDTA - Mg (or Zn) excess 용액加. MgY 2- + M 2+ MY 2- + Mg 2+ standard base 로적정 4 alkalimetric titration. excess Na2H2Y 를중성의금속이온에加 M 2+ + H 2 Y 2- MY 2- + 2H + standard base 로적정

scope of complexometric titrations EDTA 대부분의금속과 chelating 선천성 : ph regulation에의해가능 ph1의용액 M 2+ 방해없이 M 3+ 정량가능 ph 에서 EBT 지시약으로적정 : Mg 방해없이 Cd만정량可. Cd, Co, Cu, Ni, Zn, Pd를 CN - 로 masking Mg, Ca 정량. Determination of water hardness hardness : the capacity of a water sample to ppt. 주로 Ca, Mg 많이 CaCO 3 당량으로표시 ph 10에서 Calmagite, Eriochremeblack T를지시약으로사용하여정량.