Kesetimbangan asam-basa adalah salah satu dari ketentuan yang terjadi pada hukum alam yang mendasari penciptaan dan keteraturan makromos. Titrasi asam basa melibatkan asam maupun basa seabgai titer ataupun titrant, titrasi asam basa berdasarkan reaksi penetralan. Kadar larutan asam ditentukan dengan menggunakan larutan basa dan sebaliknya. Laporan Praktikum Stoikiometri Pdf Download - DOWNLOAD.
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- Titrasi Presipitasi
- Outline1. Essence and classification of methodsprecipitation titration2. Titration Curves3. Argentometry3. Argentometry4. Thiocyanatometry5. Mercurometry6. Sulphatometry7. Hexacianoferratometry
- Precipitation TitratonsPrecipitation titrimetry, which is based onreactions that yield ionic compounds of limitedsolubility, is one of the oldest analyticaltechniques. The slow rate of formation of mostprecipitates, however, limits the number ofprecipitating agents that can be used in titrationsprecipitating agents that can be used in titrationsto a handful. The most widely used and importantprecipitating reagent, silver nitrate, which is usedfor the determination of the halogens, thehalogen-like anions. Titrations with silver nitrateare sometimes called argentometric titrations.
- RequirementsThe analyte should be dissolved in water andgive an ion which would be active inprecipitation reaction.The precipitate should be practically insoluble(K
- Classification of precipitation titrationmethods (based on titrant):1. Argentometry2. Thiocyanatometry3. Mercurometry3. Mercurometry4. Sulphatometry5. Hexacianoferratometry
- 2. Titration CurvesCurve plotting of titration is based on a ruleof solubility product.And accordinglynBmABAnmnm BAKsp ][][
- The Shapes of Titration CurvesTitration curves for precipitation reactions arederived in a completely analogous way to themethods described for titrations involving strongacids and strong bases. P-functions are derived forthe preequivalence-point region, the post-equivalence point region, and the equivalenceequivalence point region, and the equivalencepoint for a typical precipitation titraton.Most indicators for argentometric titrationsrespond to changes in the concentration of silverions. As a consequence, titraton curves forprecipitation reactions usually consist of a plot ofpAg versus volume of AgNO3.
- Precipitation titration curve for 50.0 mL of0.0500 M Cl with 0.100 M Ag+. (a) pClversus volume of titrant; (b) pAg versusvolume of titrant.
- The factors which define value ofinflection points of titration on curves ofprecipitation titrationConcentration of titrant solutions and theanalyte (the higher the concentration, thesharper the slope of the inflection point.)sharper the slope of the inflection point.)Solubility of a precipitate (The smaller thesolubility, the sharper the slope of theinflection point)
- Influence of precipitate solubility ontitration inflection point
- Influence of other factors on inflectionpoint of the precipitation titrationTemperature (the higher the temperature,the higher the solubility of a precipitateand the less sharp slope inflection point)and the less sharp slope inflection point)Ionic strength of the solution (the higherthe ionic strength of a solution, the higherthe solubility of a precipitate and the lesssharp slope inflection point)
- Titration of 50 mL of 0.05 M NaCl by0.1000M AgNO3 continuedpAg = log 10[Ag+].Precipitation AgClVolume AgNO3Sharp increase inFree Ag+
- Successful titrations of ions by SiverNitratepAg = log 10[Ag+].Precipitation AgIPrecipitation AgBrVolume AgNO3A Sharp increase inFree Ag+ signals the endpoint in each casePrecipitation AgCl
- Successful titrations of Mixtures by SiverNitratepAg = log 10[Ag+].Precipitation AgI firstVolume AgNO3A Sharp increase inFree Ag+ signals the endpoint in each casePrecipitation AgCl second
- Sigmoidal titration curve Linear segment titration curve.Spectrophotometric titrationcurve of transferrin with ferricnitriloacetate.
- Titration curve for the titration of 50.00 ml of 0.1000M AgNO3 with0.1000M KSCN.
- Factors influencing the sharpness of end points1) Reagent concentration[T], [A] eT2) Completeness of reactionSolubility e.p. change jumpI Ksp=8.3 1017I Ksp=8.3 10Br Ksp=5.0 1013Cl Ksp=1.8 1010IO3 Ksp=3.0108BrO3 Ksp=5.7105
- Titration of a mixture by potentiometric detectionTwo precipitable ions(ex. Cl, I)Titrant (ex. Ag+)Ex. 0.0502M KI + 0.0500M KClEx. 0.0502M KI + 0.0500M KCl0.0845 M AgNO3Ksp AgI
- Titration curves for 50.0 ml of a solution 0.0800 M in Cl and 0.0500 M inI or Br.
- End Point for Argentometric TitrationsThree types of end points are: (1) chemical, (2)potentiometric, (3) amperometric. Potentiometricend points are obtained by measuring the potential.To obtain an amperometric end point, the currentgenerated between a pair of silver microelectrodes ismeasured and plotted as a function of reagentmeasured and plotted as a function of reagentvolume. The chemical end point consists of a colorchange or the appearance or disappearance ofturbidity. The requirements are (1) the color changeshould occur over a limited range in the p-function,and (2) the color change should take place within thesteep portion of the titration curve.
- 3. ArgentometryThis is a precipitation titration in which Ag+ is the titrant.X- + Ag+ = AgXwhere: X- = Cl-, Br-, I-, CN-, SCN-, etc.. Titrant: AgNO3 secondary standard solution Titrant: AgNO3 secondary standard solution Standardization n primary standard solution ofSodium chlorideAgNOAgNO33 ++ NaClNaCl AgCl + NaNO+ NaNO33Indicator for standardization - 5 % Potassium chromateK2CrO4 (to appearance reddish-brown precipitate ofSilver chromate):2AgNO2AgNO33 ++ K2CrO4 Ag2CrO4+ 2KNO+ 2KNO33..
- Argentometry:without indicator: Gay-Lussac method (method of eventurbidity) method to point enlightenmentwith indicator: Mohr method Fajans Fisher Khodacov method Volhard method
- Gay-Lussac method (method ofeven turbidity)If solution NaBr titrate by solution AgNO3 (or on thecontrary) there is a reaction:Br- + Ag+ = AgBr For determination of equivalence point it is For determination of equivalence point it isnecessary to select two identical portions of asolution before the titration end. To one of themadd a drop of AgNO3 solution, on another - a dropof NaBr solution at the same concentration.Titration will finish when there will be identicalintensity of turbidity in both portions of solution.
- Method to enlightenment point The method of titration to an enlightenment point canbe applicable when insoluble compounds is in colloidalstate. For example, determination of - ions by silvernitrate, Ag forms, it is adsorbing - and receivenegative charges (colloidal solution of Ag forms).As more and more - ions react with Ag+ ions, particles As more and more - ions react with Ag+ ions, particlesAg gradually lose adsorbed by them - ions, and theircharge decreases. In the end of titration occurcoagulation of particles and their sedimentation. Thesolution thus is absolutely clarified.
- Formation of a Colored PrecipitateThe Mohr MethodSodium chromate can serve as an indicator for theargentometric determination of chloride, bromide,and cyanide ions by reacting with silver ion to form abrick-red silver chromate (Ag2CrO4) precipitate in theequivalence-point region. The reactions involved inthe determination of chloride and bromide (X-) aretitration reaction: Ag+ + X- AgX(s) [white]indicator reaction: 2Ag+ + CrO42- Ag2CrO4(s)[red]The solubility of silver chromate is several timesgrater than that of silver chloride or silver bromide.
- Mohr method Titrant: AgNO3 secondary standard solution Stanardization on primary standard solution ofsodium chloride NaCl (by a measured volumeof primary standard solution):AgNOAgNO33 ++ NaClNaCl AgCl + NaNO+ NaNO33 Indicator - 5 % potassium chromate K2CrO4 (toformation precipitate of reddish-brownformation precipitate of reddish-brownAg2CrO4):2AgNO3 + K2CrO4 = Ag2CrO4+ 2KNO3 Determinate substance: chloride Cl-, bromideBr-. Medium: ~ 6,5-10,3. Usage: quantitative definition of sodiumchloride, potassium chloride, sodium bromide,potassium bromide, etc.
- Restrictions of usage of Mohr method: It is impossible to use titation in acidic solutions:2CrO42- + 2H+ = Cr2O72- + H2O It is impossible to use titration in the presence ofammonia, etc. ions, molecules which can beligands on relation to Silver ionsIt is impossible to use titration in the presence ofmany cations (Ba2+, Pb2+, etc.) which form themany cations (Ba , Pb , etc.) which form thepainted precipitates with chromate ions CrO42-It is impossible to use titration in the presence ofreducers which reduce chromate ions CrO42- toCr3+ ionsIt is impossible to use titration in the presence ofmany anions (PO43-, AsO43-, AsO33-, S2- etc.)which with Silver ions give the painted precipitates
- Adsorption Indicators: The Fajans MethodAn adsorption indicator is an organic compound thattends to be adsorbed onto the surface of the solid ina precipitation titration. Ideally, the adsorption occursnear the equivalence point and results not only in acolor change but also in a transfer of color from thesolution to the solid (or the reverse).Fluorescein is a typical adsorption indicator useful forFluorescein is a typical adsorption indicator useful forthe titration of chloride ion with silver nitrate. Inaqueous solution, fluorescein partially dissociatesinto hydronium ions and negatively chargedfluoresceinate ion that are yellow-green. Thefluoresceinate ion forms an intensely red silver salt.Titrations involving adsorption indicators are rapid,accurate, and reliable.
- Fajans Fisher Khodacov method Titrant: AgNO3 secondary standardsolution Standardization on primary standardsolution of sodium chloride NaCl (by ameasured volume of primary standardsolution):solution):Medium: ~ 6,5-10,3 (for determination ofclorides) and ~ 2,0-10,3 (fordetermination of bromides and iodides).Indicators of method: dichlorofluoroscein (for determination of clorides) eosine (for determination bromides and iodides)
- The mechanism of indicators actionAgNO3 + NaCl = AgCl + NaNO3HInd H+ + Ind-Adsorption indicator whose color when adsorbedto the precipitate is different from that when it is insolution
- ColourIndicatorIndicator SolutionSolution Surface ofSurface ofprecipitateprecipitateDichloro-fluorosceingreenish yellow pinkeosineeosine yellowishyellowish--redred redishredish -- violetvioletA number adsorption abilities of anion at ~7on a precipitate surface of Silver chlorideI- > CN- > SCN- > Br- > eosine > l- >dichlorofluoroscein > NO3- > ClO4-eosineeosine yellowishyellowish--redred redishredish -- violetviolet
- Conditions of titration: Acidity of solutions Concentration of reacting solutions The account adsorption abilities of indicatorsand ions which present in a solution Titration near equivalence point is necessaryto spend slowlyto spend slowly Titration with adsorption indicators spend in adiffused lightUse:Quantitative definition of chlorides, bromides,iodides, thiocyanides, cyanides.
- The Volhard Method (Colored Complex)In the Volhard method, silver ions are titrated with astandard solution of thiocyanate ion:Ag+ + SCN- AgSCN(s)Iron (III) serves as the indicator. The solution turnsred with the first slight excess of thiocyanate ion:Fe3+ + SCN- Fe(SCN)2+redThe titration must be carried out in acidic solution toprevent precipitation of iron(III) as the hydratedoxide.KFe SCNFe SCNf ( ).105 103-2+3+
- continuedThe most important application of theVolhard method is for the indirectdetermination of halide ions. A measuredexcess of standard silver nitrate solution isexcess of standard silver nitrate solution isadded to the sample, and the excess silverion is determined by back-titration with astandard thiocyanate solution.
- Volhard method Titrant: AgNO3, ammonium or potassiumthiocyanide NH4SCN, KSCN - secondarystandard solutionStardadization AgNO3 on primary standardsolution NaCl, NH4SCN, KSCN onstandardization solution AgNO3:AgNO3 + NH4SCN = AgSCN + NH4NO3AgNO3 + NH4SCN = AgSCN + NH4NO3Indicator by standardization of ammoniumor potassium thiocyanide with iron () salts(NH4Fe(SO4)212H2O in presence of nitricacid) to the formation of the reddish coloredFe(SCN)2+ complex:Fe3+ + SCN- = [Fe(SCN)]2+
- Medium: in presence of nitric acid Indicators of method: iron () saltsNH4Fe(SO4)212H2O in presence of nitricacidDeterminate substance: halogenides,thiocyanides, cyanides, sulphides,carbonates, chromates, oxalates, arsenatesetc.
- Until equivalence point (e.p.)Hal- + Ag+ (excess) = AgHalAg+(rest) + SCN- = AgSCNAfter e. p.Fe3+ + SCN- = [Fe(SCN)]2+(reddish)!!! At determination of iodides the indicator is added in theend of titration to avoid parallel:end of titration to avoid parallel:2Fe3+ + 2I- = 2Fe2+ + I2Advantages of Volhard methodTitration possibility:In very acidic solutions In the presence of many cations which interfere bydefinition in Mohr method
- End point detection in argentometric titrationDetection techniques in precipitation titrations : Indicator Potentiometry Light scattering / turbidimetry of nephelometryTitration Mohr Volhard FajansTitration Ag+ + Cl AgCl Ag+ + Cl AgCl Ag+ + Cl AgClreaction white Back titration :Ag+ + SCN AgSCNwhitewhiteEnd point 2Ag+ + CrO42 Ag2CrO4 SCN + Fe3+ FeSCN2+ Electric doublelayerreaction red soluble red with adsorptionInd.pH 7~10.5 Kf= 1.05103DichlorofluoresceinUse Cl , Br , CN Cl , Br , I Cl , Br , I , SCNNo use I , SCN
- Table 13-3, p.362
- 4. Thiocyanatometry This is a precipitation titration in which SCN- is thetitrant. Titrant: ammonium or potassium thiocyanideNH4SCN, KSCN - secondary standard solution Stardadization: on primary standardsolution of AgNO3:AgNO + NH SCN = AgSCN + NH NOAgNO3 + NH4SCN = AgSCN + NH4NO3Indicator by standardization of ammoniumor potassium thiocyanide with iron () salts:Fe3+ + SCN- = [Fe(SCN)]2+ Medium: in presence of nitric acid Indicator: iron () salts NH4Fe(SO4)212H2O inpresence of nitric acid
- Determine substance: drugs, which contain Silver(Albumosesilber, colloid silver - Kollargol, silvernitrate).!!! At the analysis of drugs which containnonionic silver, preliminary it is heated withsulphuric and nitric acids (receive ioniccompound).compound).!!! At determination of iodides the indicator is addedin the end of titration to avoid parallel:2Fe3+ + 2I- = 2Fe2+ + I2
- Advantages of ThiocyanatometryTitration possibility:In very acidic solutions In the presence of many cations whichinterfere by determination in Mohrmethodmethod
- 5. Mercurometry Mercurometry this is a precipitationtitration in which Hg22+ is the titrant2Cl- + Hg22+ = Hg2Cl2 Ksp = 1,310-182I- + Hg22+ = Hg2I2 Ksp = 4,5 10-29Titrant: Hg2(NO3)2 - secondary standardsolutionStardadization: on primary standardsolution of NaCl:Hg2(NO3)2 + 2NaCl = Hg2Cl2 + 2NaNO3
- Indicators: 1) solution of iron () thiocyanide (fromreddish to colourless)2Fe(SCN)2+ + Hg22+ = Hg2(SCN)2 + 2Fe3+!!! For the account of titrant volume which is used onindicator titration, do blind test2) 1-2 % spirit diphenylcarbazone (to blue2) 1-2 % spirit diphenylcarbazone (to bluecolor)!!! Indicator is added before end of titrationDeterminate substance: chlorides and iodides. Medium: very acidic (may be to 5 mol/L H+ ions).
- Advantages of mercurometry: Possibility usage titration in very acidic solutions Titrant is cheaper Mercury (I) Salt...