Aplikasi Kesetimbangan Kimia Utk Analisis Qualitative Anorganik

RENCANA KULIAH KIMIA ANALISA DASAR I

NoMateriWaktuDosen1Pendahuluan/ Definisi dan Ruang Lingkup12 Februari 2013A. Sabarudin2Aplikasi Kesetimbangan Kimia dalam analisis kualitatif anorganik (part 1)19 Februari 2013A. Sabarudin3Aplikasi Kesetimbangan Kimia dalam analisis kualitatif anorganik (part 2)26 Februari 2013A. Sabarudiin4Quiz 1 dan Tugas 15 Maret 2013A. Sabarudin5Libur: Hari Raya Nyepi12 Maret 20136Analisis kualitatif anorganik : identifikasi dan reaksi pendahuluan19 Maret 2013A. Sabarudin7Sistematika analisis kualitatif berdasarkan penggolongan26 Maret 2013A. Sabarudin8UTS1-12 April 20139UTS1-12 April 201310Reaksi pengenalan kation (part 1)16 April 2013Qonita Fardiyah11Reaksi pengenalan kation (part 2)23 April 2013Qonita Fardiyah12Reaski pengenalan anion (part 1)30 April 2013Qonita Fardiyah13Reaksi pengenalan anion (part 2)7 Mei 2013Qonita Fardiyah14Quiz 2 dan Tugas 214 Mei 2013Qonita Fardiyah15Reaksi-reaksi Khusus (part 1)21 Mei 2013Qonita Fardiyah16Reaksi-reaksi Khusus (part 2)28 Mei 2013Qonita Fardiyah

Aplikasi Kesetimbangan Kimia Dalam Analisis Kualitatif Anorganik

Kesetimbangan Kimia ??Kesetimbangan Reaksi Asam-BasaKesetimbangan Reaksi PengendapanKesetimbangan Reaksi Pengomplekan Kesetimbangan Reaksi Oksidasi Reduksi

Forming Ionic CompoundsTransition metals generally exhibit more than one oxidation state.Cations are often complex ions species where the transition metal ion is surrounded by a certain number of ligands (Lewis bases).

The Complex Ion Co(NH3)63+

Ionic Compounds with Transition MetalsMost compounds are colored because the transition metal ion in the complex ion can absorb visible light of specific wavelengths.

Oxidation States and Species for Vanadium in Aqueous Solution

Typical Chromium Compounds

Some Compounds of Manganese in Its Most Common Oxidation States

Typical Compounds of Iron

Typical Compounds of Cobalt

Typical Compounds of Nickel

Typical Compounds of Copper

Chapter SixteenPrentice-Hall 2002Slide * of 32

The Solubility Product Constant, KspThe solubility product constant, Ksp, is the product of the concentrations of the ions involved in a solubility equilibrium, each raised to a power equal to the stoichiometric coefficient of that ion in the chemical equation for the equilibrium.


The Solubility Equilibrium Equation And KspCaF2 (s) Ca2+ (aq) + 2 F- (aq)Ksp = [Ca2+][F-]2Ksp = 5.3x10-9

As2S3 (s) 2 As3+ (aq) + 3 S2- (aq)Ksp = [As3+]2[S2-]3


Some Values For Solubility Product Constants (Ksp) At 25 oC


Ksp And Molar SolubilityThe Ksp is related to the solubility of an ionic solute,

But Ksp and molar solubility (the molarity of a solute in a saturated aqueous solution) - are not the same thing.

Calculating solubility equilibria fall into two categories: determining a value of Ksp from experimental data calculating equilibrium concentrations when Ksp is known.


Calculating Ksp From Molar SolubilityIt is found that 1.2x10-3 mol of lead (II) iodide, PbI2, dissolves in 1.0 L of aqueous solution at 25 oC. What is the Ksp at this temperature?


Calculating Molar Solubility From KspCalculate the molar solubility of silver chromate, Ag2CrO4, in water from Ksp = 1.1x10-12 of Ag2CrO4.


The Common Ion Effect In Solubility EquilibriaThe common ion effect is an event that occurs when an ionic equilibrium shifts due to the addition of a solute that contains an ion that is the same as an existing ion in the equilibrium.


Solubility Equilibrium Calculation-The Common Ion EffectWhat is the solubility of Ag2CrO4 in 0.10 M K2CrO4? Ksp = 1.1x10-12 for Ag2CrO4.

Comparison of solubility of Ag2CrO4In pure water:6.6 x 10-5 MIn 0.10 M K2CrO4:1.7 x 10-6 MThe common ion effect!!


Determining Whether Precipitation OccursQip is the ion product reaction quotient and is based on initial conditions of the reaction.Qip can then be compared to Ksp.To predict if a precipitation occurs:- Precipitation should occur if Qip > Ksp.- Precipitation cannot occur if Qip < Ksp. - A solution is just saturated if Qip = Ksp.


Determining Whether Precipitation Occurs An ExampleThe concentration of calcium ion in blood plasma is 0.0025 M. If the concentration of oxalate ion is 1.0x10-7 M, do you expect calcium oxalate to precipitate? Ksp = 2.3x10-9.

Three steps:Determine the initial concentrations of ions.Evaluate the reaction quotient Qip.Campare Qip with Ksp.


Determining Whether Precipitation Occurs An ExampleIn applying the precipitation criteria, the effect of dilution when solutions are mixed must be considered.

Example:A 250.0 mL sample of 0.0012 M Pb(NO3)2 (aq) is mixed with 150.0 mL of 0.0640 M NaI (aq). Should precipitation of PbI2 (s), Ksp = 7.1x10-9, occur?


Determining Whether Precipitation Occurs Another ExampleHow many grams of KI should be dissolved in 10.5 L of 0.00200 M Pb(NO3)2 solution so that precipitation of PbI2 (s) will just begin? Ksp = 7.1x10-9


Determining Whether Precipitation Is CompleteA slightly soluble solid never totally precipitates from solution, but we generally consider precipitation to be essentially complete if about 99.9% of the target ion is precipitated and only 0.1% or less is left in solution.Three conditions that generally favor completeness of precipitation are:A very small value of Ksp.A high initial concentration of the target ion.A concentration of common ion that greatly exceeds that of the target ion.


Determining Whether Precipitation Is Complete - An ExampleA 0.50 L solution of 0.0010 M BaCl2 is added to 0.50 L solution of 0.00010 M Na2SO4. Will the precipitation of SO42- as BaSO4 (s) be complete? Ksp = 1.1x10-10.


Selective PrecipitationThe first precipitate to form when AgNO3(aq) is added to an aqueous solution containing Cl- and I- is yellow AgI(s).Essentially all the I- has precipitated before the precipitation of white AgCl(s) begins.


Selective Precipitation An ExampleExample An aqueous solution that is 2.00 M in AgNO3 is slowly added from a buret to an aqueous solution that is 0.0100 M in Cl- and also 0.0100 M in I-AgCl (s) Ag+ (aq) + Cl- (aq)Ksp = 1.8x10-10AgI (s) Ag+ (aq) + I- (aq)Ksp = 8.5x10-17Which ion. Cl- or I-, is the first to precipitate from solution?When the second ion begins to precipitate, what is the remaining concentration of the first ion?Is separation of the two ions by selective precipitation feasible?


Effect of pH on SolubilityThe solubility of an ionic solute may be greatly affected by pH if an acid-base reaction also occurs as the solute dissolves.If the anion of the precipitate is that of a weak acid, the precipitate will dissolve somewhat when the pH is lowered; if, however, the anion of the precipitate is that of a strong acid, lowering the pH will have no effect on the precipitate.Since CO2 is lost from the reaction of an insoluble carbonate with acid, this concept does not apply.


Effect of pH on Solubility - An ExampleDetermine the molar solubility of Fe(OH)3 in pH = 2.70 buffer. Ksp = 4.0x10-38 for Fe(OH)3.


Qualitative Inorganic AnalysisAcid-base chemistry, precipitation reactions, oxidation-reduction, and complex-ion formation all come into sharp focus in an area of analytical chemistry called classical qualitative inorganic analysis.Qualitative signifies that the interest is in determining what is present, not how much is present.Although classical qualitative analysis is not as widely used today as instrumental methods, it is still a good vehicle for applying all the basic concepts of equilibria in aqueous solutions.



Cations of Group 1If aqueous HCl is added to an unknown solution of cations, and a precipitate forms, then the unknown contains one or more of these cations: Pb2+, Hg22+, or Ag+.These are the only ions to form insoluble chlorides.If there is no precipitate, then these ions must be absent from the mixture.If there is a precipitate, it is filtered off and saved for further analysis.The supernatant liquid is also saved for further analysis.


Cation Group 1 (continued)Analyzing For Pb2+Of the three possible ions in solution, PbCl2 is the most soluble in water.The precipitate is washed with hot water and the washings then treated with aqueous K2CrO4.If Pb2+ is present, chromate ion combines with lead ion to form a precipitate of yellow lead chromate, which is less soluble than PbCl2.If Pb2+ is absent, then the washings just become tinged yellow but no precipitate is in evidence.


Cation Group 1 (continued)Analyzing For Ag+Next, the undissolved precipitate is treated with aqueous ammonia.If AgCl is present, it will dissolve in this solution.If there is any remaining precipitate, it is separated from the supernatant liquid and saved for further analysis.The supernatant liquid (which contains the Ag+, if present) is then treated with aqueous nitric acid.If a precipitate reforms, then Ag+ was present in the solution, if no precipitate forms, then Ag+ was not present in the solution.


Cation Group 1 (continued)Analyzing For Hg22+When precipitate was treated with aqueous ammonia in the previous step, any Hg22+ underwent an oxidation-reduction reaction to form a dark gray mixture of elemental mercury and HgNH2Cl that precipitates from the solution.If this dark gray precipitate was observed, then mercury was present in the original unknown sample.If this dark gray precipitate was not observed, then mercury must have been absent from the original unknown sample.


Group 1 Cation Precipitatesleft: cation goup 1 ppt: PbCl2, PbCl2, AgCl (all white)middle: product from test for Hg22+: mix of Hg (black) and HgNH2Cl (white)right: product from test for Pb2+: PbCrO4 (yellow) when K2CrO4(aq) is reacted with saturated PbCl2



Hydrogen Sulfide In TheQualitative Analysis SchemeH2S is a weak diprotic acid; there is very little ionization of the HS- ion and it is the precipitating agent.H2S (aq) + H2O H3O+ (aq) + HS- (aq) Ka1 = 1.0x10-7HS- (aq) + H2O H3O+ (aq) + S2- (aq)Ka2 = 1.0x10-19

H2S (aq) + H2O H3O+ (aq) + HS- (aq) M2+ (aq) + HS- (aq) + H2O (l) MS (s) + H3O+ (aq) Overall: M2+ (aq) + H2S (aq) + 2 H2O (l) MS (s) + 3 H3O+ (aq)


Cation Groups 2, 3, 4 And 5The concentration of HS- is so low in a strongly acidic solution, that only the most insoluble sulfides precipitate.These include the eight metal sulfides of Group 2.Of the eight cations in Group 3, five form sulfides that are soluble in acidic solution but insoluble in an alkaline ammonia/ammonium chloride buffer solution. The other three group 3 cation form hydroxide precipitates in the alkaline solution.The cations of groups 4 and 5 form soluble sulfides, even in basic solution.



Cation Groups 2, 3, 4 And 5The hydroxides of Groups 4 and 5, with the exception of Mg2+, are also moderately or highly soluble.The group 4 cations are precipitated as carbonates from a buffered alkaline solution.The cations of group 5 remain soluble in the presence of all common reagents.Within each of the qualitative analysis groups, additional reactions to dissolve group precipitates and to separate and selectively precipitate individual cations for identification and confirmation are used.


SummaryThe solubility product constant, Ksp, represents equilibrium between a slightly soluble ionic compound and its ions in a saturated aqueous solution.The common ion effect is responsible for the reduction in solubility of a slightly soluble ionic compound.Precipitation is assumed to be complete if no more than 0.1% of the target ion remains in solution.The solubilities of some slightly soluble compounds depends strongly on pH.


SummaryPrecipitation, acid-base, and oxidation-reduction reactions, together with complex-ion formation, are all used extensively in the classical scheme for the qualitative analysis of common cations.

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Aplikasi Kesetimbangan Kimia Utk Analisis Qualitative Anorganik

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