Chapter 16 Applications of Neutralization Titrations
16A Reagents for Neutralization Titrations strong acid or base : eq. point 에서명확한 ph 변화有 standard solution 으로사용 16A-1 Preparation of Standard Acid Solutions acid standard soln. 종류 HCl: 묽은용액의경우매우안정 0.1M HCl 1 hr 동안 boiling 로해도농도의 loss 없음 0.5M HCl 10 min 동안 boiling 로해도농도의 loss 없음 HClO 4, H 2 SO 4 사용. HNO 3 산화성으로인해不用 acid standard soln. 제조 1 dilution primary standard base 로 standardization 2 less frequently careful density measurement 3 by distillation of the concentrated reagent ; (constant boiling HCl) 대기압에따라농도변화 acid 1 eq. 을갖는 distillate 의공기중의무게 (P = 670 ~ 780 torr)
16A-2 The Standardization of Acids Sodium Carbonate Primary-standard grade 의 Na 2 CO 3 또는 purified sodium hydrogen carbonate 을 270 ~ 300 에서 1hr 동안加열. 2 개의 end point 관찰 standardization 시 2 번째 end point 를사용 1 st end point step ; ph 8.3 부근 2 nd end point ; ph 3.8 부근 always used for standardization (ph 변화크기때문 ) BCG, methyl orange 지시약사용 H 2 CO 3 CO 2 (g) + H 2 O ; HCO 3-, CO 3 2- 의 buffer 파괴 boiling * 적정시용액 boiling CO 2 제거
Other Primary Standards for Acids 1Tris-(hydroxymethyl)aminomethane(HOCH 3 ) 3 CNH 2 TRIS or THAM. 2 sodium tetraborate 3 mercury(Ⅱ)oxide 4 calcium oxide.
16A-3 Preparation of Standard Solutions of Base Sodium hydroxide is the most common base for preparing standard solutions, although potassium hydroxide and barium hydroxide are also used. These bases cannot be obtained in primary-standard purity, and so, all must be standardized after they are prepared. NaOH ; (or KOH, Ba(OH)2) the soln must be standardized. * glass, atmosphere에장기간접촉하지않는한안정. NaOH + glass silicate 形成 보관 : polyethylene bottle or glass bottle that has been coated with paraffin.
The Effect of Carbon Dioxide on Standard Base Solutions Na, K, Ba 의수산화물 atmospheric CO 2 와 rapidly react CO 2 + 2OH - CO 3 2- + H 2 O base 의 standardized soln 에의한 CO 2 의흡수는그것의 acid titer 를반드시변화시키지는않는다. acidic transition indicator 사용 (BCG) 이때 H 3 O + 2 개가소모 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 H 3 O + 1 개가소모 CO 3 2- + H 3 O+ HCO 3- + H 2 O base 의 effective concentration 감소 Carbonate error 유발 Ba(OH) 2 사용하면 CO 2 흡수하여 ppt 생성 Carbonate error CO 2 + Ba 2+ 2OH - + BaCO 3 (s) + H 2 O 용액제조에사용된고체 reagent 가대기중의 CO 2 흡수 carbonate 상당량존재
* carbonate free OH - soln 제조법 염기표준용액제조에사용되는고체시약은상당량의 carbonate ion으로오염됨 standardization과 analysis시같은지시약을사용하면 carbonate error 없음 but, end point에서의변색이선명하지않음 standardization이전에 carbonate ion 제거 NaOH 용액 ; 50% aqueous soln 제조 Na 2 CO 3 의 very low solubility 利用. supernatant liquid decant하여희석후사용 ( 위용액제조시증류수묽어서식힌후사용 ) Distilled water : 끓여서 CO 2 제거, 식힌후사용 Deionized water : CO2 많이포함하고있지않음 Arrangement for the storage of standard base solutions. CO 2 흡착제 : soda lime, or astroite 적정중의 CO 2 흡수 : beaker, test tube로뚜껑 standard soln : 1주일內사용할경우 polythylene bottle에마개를사용하며可能 buret teflon stopcock 사용이좋다.
16A-4 The Standardization of Bases Potassium Hydrogen Phthalate 장점 : high molar mass 를갖는 nonhygroscopic crystalline solid.
Other Primary Standards for Bases 1 Benzoic acid: solubility in water is limited ethanol 에녹인후물에묽힘 2 potassium hydrogen iodate, KH(IO 3 ) 2 : high equivalent weight, strong acid
16B Typical Applications of Neutralization Titrations inorganic, organic, biological species ( 산, 염기의속성을갖는 ) 의정량 적정과적절한 chemical treatment 를통하여 analyte 를 acid 또는 base 로변환시킴 중화적정에서 2 type 의 end point 결정법. 1 indicator 2 ph meter (Potentiometry, Section 21G)
16B-1 Elemental Analysis Carbon, nitrogen, chlorine, brine, sulfur, phosphorus & fluorine inorganic acid or base 로 convert 시켜적정 Types of samples: proteins, synthetic drugs, fertilizers, explosives, Nitrogen soils, portable water supplies, dyes
1 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, azo & 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.
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
Sulfur Sulfur (organic and biological materials) 연소 (with O 2 ) SO 2 (or SO 3 ) 발생 H 2 O 2 에흡수 H 2 SO 4 생성 적정
16B-2 The Determination of Inorganic Substances Ammonium Salts Ammonium salt with strong base ammonia 로변환 distillation Kjeldahl method 로적정 Nitrates and Nitrites Nitrate, nitrite ammonium ion distillation Kjeldahl method 로적정 염기성조건에서환원제 (alloys) 를사용하여환원 Devarda s alloy(50% Cu, 45% Al, 5% Zn) Arnd s alloy (60% Cu, 40% Mg)
Carbonate and Carbonate Mixtures
16B-3 The Determination of Organic Functional Groups Carboxylic and Sulfonic Acid Groups Carboxylic acid 의 Ka = 10-4 ~ 10-6 쉽게적정가능 ( 염기성영역에서변색하는지시약사용 ) 물에잘녹지않는 Carboxylic acid 1) ethanol 에녹인후 aqueous base 로적정 2) 과량의염기표준용액에녹인후산표준용액으로역적정 Sulfonic acid : 강산, 물에잘녹음염기로적정 순수한유기산의 equivalent weight 결정에사용
Amine Groups Aliphatic amine Kb 10-5, saturated cyclic amine (piperidine) 강산으로직접적정 Aromatic amine (aniline) Kb 10-10, cyclic amine with aromatic character (pyridine) nonaqueous solvent (anhydrous acetic acid) 에서적정 Ester Groups Ester 과량의염기첨가 saponification 남은염기를산표준용액으로적정
Hydroxyl Groups Hydroxyl group + carboxylic acid anhydrides or chlorides esterification Acetic anhydride와 phthalic anhydride 가사용됨 Ex) Acetic anhydride를사용할경우 (pyridine 에시료와 Acetic anhydride를녹임 ) 반응완결후물첨가 미반응 anhydride 가가수분해됨 acetic acid 생성 alcoholic sodium or potassium hydroxide 표준용액으로적정 Blank titration 을실시하여최초 anhydride 의양을결정 Amine 이존재하면 Acetic anhydride 에의해정량적으로 amide 로전환됨 방해작용의요인이됨 correction 필요
Carbonyl Groups Aldehyde, keton NH2OH HCl oxime + HCl HCl 을 base 로적정 Aldehyde: 30 분반응시킴 Keton : 1 시간또는더이상 refluxing
16B-4 The Determination of Salts The total salt content of a solution can be determined accurately by acid/base titration. The salt is converted to an equivalent amount of an acid or base by passing a solution containing the salt through a column packed with an ion-exchange resin. (This application is considered in more detail in Section 31D.) Standard acid or base solutions can also be prepared with ion-exchange resins. A solution containing a known mass of a pure compound, such as sodium chloride, is washed through the resin column and diluted to a known volume. The salt releases an equivalent amount of acid or base from the resin. The concentration of the acid or base can then be calculated from the known mass of the original salt. 29
Summary Application of Acid-Base titration, Standard solution, Standardization, Primary standard, acid neutralization capacity Solutions of 0.1 M HCl, HClO 4, H 2 SO 4, HNO 3 constant boiling HCl, TRIS-(hydroxymethyl)aminomethane Sodium carbonate, washing soda, trona, Borax (= sodium tetraborate ), HgO, Potassium acid phthalate, Potassium hydrogen phthalate, Sulfamic acid ( H 2 NSO 3 H), Potassium hydrogen iodate, Benzoic acid NaOH, KOH, Ba(OH) 2, carbonate error Kjeldahl nitrogen determinations, Ammonium salt, nitrate, nitrite Carbonate and Carbonate Mixtures, Winkler method, Biuret method, Lowry method, Organic functional group, saponification, esterification, Oxime, Sorenson formol titration, Titration of liberated acid by base, lemon oil, thiotepa, Alkaloid, morphine, esters acid-base back titration Salt, ion exchange resin 30