슬라이드 1

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1 Chapter 20 Applications of Oxidation/Reduction Titrations

2 20A Auxiliary Oxidizing and Reducing Regents Analyte single oxidation state pretreatment 필요함 20A-1 Auxiliary Reducing Regents Metal: Zn, Al, Cd, Pb, Ni, Cu, Ag(Cl - 존재시 ) stick, coil, granule 형태로사용 Ex) Jones reductor: 직경 2cm, 높이 40~50cm Zinc amalgam 사용 2Zn(s) + Hg 2+ Zn 2+ + Zn(Hg)(s)

4 20A-2 Auxiliary Oxidizing Regents Sodium Bismuthate 강력한산화제 : Ex) Mn(II) permanganate Sparingly soluble solid : analyte 용액에넣고잠시끓임 analyte 산화시킨후 filter 로걸러서제거 Ammonium Peroxydisulfate Excess reagent 끓이면빠른시간내에쉽게분해됨 Cr(III) dichromate, Ce(III) Ce(IV), Mn(II) permanganate 로산화시킴 Sodium Peroxide and Hydrogen Peroxide Solid sodium salt 또는 acid solution 형태로사용 반응후끓여서 excess reagent 제거

5 20B Applying Standard Reducing Regents 20B-1 Iron(II) Solutions Fe(NH 4 ) 2 (SO 4 ) 2 6H 2 O (Mohr s salt), FeC 2 H 4 (NH 3 ) 2 (SO 4 ) 2 4H 2 O(Oesper s salt) 를사용하여제조 Air oxidation (in neutral solution) acid solution(~0.5 M H 2 SO 4 ) oxidation 억제 Oxidizing agents excess Standard Fe(II) 첨가 excess Fe(II) 를 potassium dichromate 또는 Ce(IV) 로역적정 Organic peroxides, hydroxylamine, chromium(vi), cerium(iv), nitrate, chlorate, perchlorate 등과 numerous other oxidant (Problem 20-37, 20-39) 정량에사용

6 20B-2 Sodium Thiosulfate Moderately strong reducing agent Intermediate로 iodine이발생하는산화제를 indirect 과정으로정량하는데사용됨 Iodine과반응시다음의과정에의해정량적으로 tetrathionate ion 이됨 2S 2 O 2-3 S 4 O e- Ex) OCl - 정량

7 Detecting End Points in Iodine/Thiosulfate Titrations 1 I 2 자체색변화 : 5ⅹ10-6 M I 2 색구별가능 Analyte solution 이무색이면 iodine 색이없어지는지점이 end point 2 starch indicator 사용 분해가되므로사용직전제조 iodine 의농도가진하면 starch 분해됨 sodium thiosulfate 로 iodine 을적정할경우 ( 간접적정 ) 적정이거의끝날무렵에 starch 가함 Thiosulfate 용액을 iodine 으로직접적정할경우 지시약을처음부터넣어줌

8 Stability of Sodium Thiosulfate Solutions Air oxidation 에는안정 다음반응에의해분해됨 - ph, microorganism, 용액의농도, Cu(II), 햇빛노출등의영향받음 - 용액 Acidic 분해속도증가 Neutral or slightly basic 박테리아대사에의해 sulfite 와 sulfate 이온으로분해 적당한살균상태만듦 (chloroform, sodium benzoate, mercury(ii) iodide 첨가시분해속도늦춤 ) 주기적으로 restandardization 하여사용

9 Standardizing Thiosulfate Solutions KIO 3 를 primary standard 로사용 : 과량의 KI 용액에 KIO 3 를녹여사용 센산으로산성화시킴 유리되는 I 2 를 thiosulfate 용액으로적정

11 Applications of Sodium Thiosulfate Solutions

12 20C Applying Standard Oxidizing Regents Reducing agent 의 standard potential, rate of reaction, stability, cost, indicator 를고려하여 oxidizing agent 선택

13 20C-1 The Strong Oxidants Potassium Permanganate and Cerium(IV) KMnO 4 를주로사용 - KMnO 4 의가격이저렴 (Ce(IV) 가격의 2%) - KMnO 4 의자체색을지시약으로이용할수있음 M 보다묽은 strong acid 용액에서 Ce(IV) 는 basic salt 침전생성 Detecting the End Points KMnO 4 : 특유의강한 purple color 를나타내며, 자체로지시약역할을함 Ce(IV) : 1,10-phenanthroline-Fe(II) complex, 또는치환된 phenanthroline 유도체 (Table 19-3) 를 indicator 로사용

14 The preparation and Stability of Standard solutions 1 KMnO 4 물을산화시키나, 산화속도가느려상당히안정 빛, 열, 산, 염기, Mn(II), MnO 2 등에의해분해촉진됨 MnO 2 불순물은걸러서사용 (filter paper 사용불가 ) 갈색병에넣어그늘진곳에보관 일주일또는이주일만에 restandardization 용액내에고체가보이면 filter 후 restandardization Excess permanganate가들어있는표준용액은가열하지말것

15 2 Cerium(IV) Primary standard grade 의 Cerium ammonium nitrate(iv) weighing standard solution 제조 0.1 M H 2 SO 4 용액에녹임 remarkable stable, 수개월보관가능, 100 가열해도농도변화없음

16 Standardizing Permanganate and Ce(IV) Solutions Primary standard: Sodium oxalate

19 Using Permanganate and Ce(IV) Solutions Table Oxidizable functional group 을가진 organic compound 들도적용가능

20C-2 Potassium Dichromate 매우안정함 ( 끓여도분해되지않음 ) HCl 과반응하지않음 Primary standard reagent 를쉽게구함 Electrode potential 은 MnO 4-, Ce(IV) 보다낮고일부 reducing agent

22 20C-2 Potassium Dichromate 매우안정함 ( 끓여도분해되지않음 ) HCl 과반응하지않음 Primary standard reagent 를쉽게구함 Electrode potential 은 MnO 4-, Ce(IV) 보다낮고일부 reducing agent 들과의반응속도가느림 Preparing Dichromate Solutions Reagent-grade K 2 Cr 2 O 7 drying (150~200 ) weighing Indicator : Diphenylamine sulfonic acid (Table 19-3)

23 Applying Potassium Dichromate Solutions Fe(II) titration Fe(II) titration 을기반으로한 oxidizing agent 들의 indirect 정량 - Analyte excess standard Fe(II) solution 첨가 standard K 2 Cr 2 O 7 solution 으로 excess Fe(II) 역적정 - Nitrate, chlorate, permanganate, dichromate ion, organic peroxide, several other oxidizing agent 정량

25 20C-3 Iodine Relatively smaller electrode potential application 제한받음 but selective 함 weak reducing agent 와공존하는 strong reducing agent 를선택적으로적정할수있음 Sensitive 하고 reversible 한 indicator 사용가능 Stability 가부족 주기적으로 restandardization 필요 Properties of Iodine solutions Iodine not very soluble in water (0.001 M) excess KI 용액에녹임 Iodine 용액은불안정함 - solute (iodine) 의휘발, 유기물과반응 (cork, rubber stopper 사용금지 ) - Air oxidation 됨 acid, heat, light 에의해촉진

26 Standardizing and applying Iodine Solutions Standardization - Primary standard materials: Anhydrous sodium thiosulfate, barium thiosulfate monohydrate - Thiosulfate 와의반응은 20-B 참고 Applications Table 20-6.

27 20C-4 Potassium Bromate as a Source of Bromine Primary standard로 Potassium Bromate 사용가능 Direct titration에는거의이용되지않음 Stable bromine source로주로사용됨 : excess Br - 첨가 Br 2 생성 Bromine 과반응하는유기물정량에사용 : 유기물시료 + excess KBrO 3 + excess KBr 산성화 과량의 KI 첨가 I 2 유리됨 유리된 I 2 를 sodium thiosulfate 로적정

28 Substitution reaction Bromine 은 substitution 또는 addition reaction 에의해유기물과반응함 Halogen substitution : aromatic ring 에있는 hydrogen 이 halogen 으로치환됨 ortho-para-dircecting group (amine, phenol) 을가진 aromatic ring 정량

30 Ex) determination of 8-hydroxyquinoline - 직접적정이가능할정도로 HCl 용액에서치환이빠르게일어남 - 8-hydroxyquinoline 은양이온들의침전제 : 8-hydroxyquinoline + 금속이온 침전회수 용해 8-hydroxyquinoline 정량 Ex) 8-hydroxyquinoline 을이용한 Al 3+ 침전형성및치환반응에의한적정 - Stoichiometric relationships: ; Al 3+ 침전 ; 침전용해 ; 치환반응

31 Addition reaction Opening of an olefinic double bond - Fat, oil, petroleum product 들의 olefinic instauration 측정 - Vitamin C tablet에서의 ascorbic acid 정량 25C-5 Determining Water with Karl Fisher Reagent Karl Fisher Titration - Solid와 liquid에포함된물의함량결정에가장많이사용 - 물에선택적인 oxidation/reduction 반응이용

32 Describing the Reaction Stoichiometry Classical Chemistry Karl Fisher reagent : pyridine, iodine, sulfur dioxide, anhydrous methanol 다음 side reaction 에의해 H 2 O 소모 excess methanol 존재시 eq 억제 Pyridine-Free Chemistry Pyridine 대신 imidazole 사용

산화와환원 1

산화와환원 1 Oxidation Reduction: The Transfer of Electrons Electrons from copper metal are transferred to silver ions. Silver metal is formed, and the solution turns blue from copper(ii) ions formed. 출처 1