Kimia AnalisisTitrasi Kompleksometri

Prinsip DasarSebagian besar ion logam membentuk senyawa koordinasi dengan suatu donor pasangan e (ligan)Mn+ + qLm- MLqn-mqKf = [MLqn-mq]/[Mn+][Lm-]qJumlah ikatan kovalen yang terbentuk disebut sebagai coordination number (misal 2,4,6)Misalnya, Cu2+ memiliki bilangan koordinasi 4Cu2+ + 4 NH3 Cu(NH3)42+Cu2+ + 4 Cl- Cu(Cl)42-

Prinsip DasarTitrasi kompleksometri yang umum untuk sampel anorganik

AnalitTitranRemarksHg(NO3)2Br-, Cl-, SCN-, CN-, tioureaProduknya kompleks merkuri(II); dapat menggunakan berbagai indikatorAgNO3CN-Produknya Ag(CN)2-; indikator nya I-; titrate to first turbidity of AgINiSO4CN-Produknya Ni(CN)42-; indicator nya AgI; titrate to first tubidity of AgIKCNCu2+, Hg2+,Ni2+Produknya Cu(CN)42-, Hg(CN)42-, Ni(CN)42-; dapat menggunakan berbagai indikator

Prinsip DasarReaksi kompleksometri yang paling penting dalam titrasi adalah yang melibatkan pembentukan kelatKelat terbentuk ketika satu ion logam berkoordinasi dengan dua atau lebih gugus donor dari ligan tunggal (membentuk cincin 5 atau 6).

Prinsip DasarTitrasi pembentukan kelatLigan dikelompokkan berdasarkan jumlah gugus donormisal, NH3 = unidentat (1 gugus donor)Glycine= bidentat(2 gugus donor)Ligan multidentat (terutama dengan 4 dan 6 donor) lebih disukai untuk titrimetri.Bereaksi lebih sempurna dengan ion logamBiasanya bereaksi dalam satu tahapMemberikan titik akhir titrasi yang lebih tajam

GambarTitration curves for complexometric titrations. Titration of 60.0 mL of a solution that is 0.020 M in metal M with (A) a 0.020 M solution of the tetradentate ligand D to give MD as the product; (B) a 0.040 M solution of the bidentate ligand B to give MB2; and (C) a 0.080 M solution of the unidentate ligand A to give MA4. The overall formation constant for each product is 1020.

Crown eter

Prinsip DasarLigan asam aminopolikarboksilatReagen paling berguna untuk titrasi kompleksometri adalah asam aminopolikarboksilat(amina tersier dengan gugus asam karboksilat) misal, ethylenediaminetetraacetic acid (EDTA)

EDTA adalah ligan heksadentatEDTA membentuk kelat stabil dengan hampir semua ion logam

GambarStructure of a metal/EDTA complex. Note that EDTA behaves here as a hexadentate ligand in that six donor atoms are involved in bonding the divalent metal cation.

Sifat keasaman EDTA

Titrasi Kompleksometri EDTA(H4Y)EDTA memiliki 4 tahap disosiasipKa1= 1.99, pKa2= 2.67, pKa3= 6,16, pKa4= 10.265 bentuk EDTA, (H4Y, H3Y-, H2Y2-, HY3-, Y4-)EDTA bereaksi dengan semua ion logam dengan rasio 1:1 Ag+ + Y4- AgY3- Fe2+ + Y4- FeY2- Al3+ + Y4- AlY- KMY = [MYn-4]/[Mn+][Y4-]

Titrasi Kompleksometri EDTA(H4Y)Konstanta pembentukan kompleks EDTA

KationKMYLog KMYKationKMYLog KMYAg+2.1 x 1077.32Cu2+6.3 x 101818.80Mg2+4.9 x 1088.69Zn2+3.2 x 101616.50Ca2+5.0 x 101010.70Cd2+2.9 x 101616.46Sr2+4.3 x 1088.63Hg2+6.3 x 102121.80Ba2+5.8 x 1077.76Pb2+1.1 x 101818.04Mn2+6.2 x 101313.79Al3+1.3 x 101616.13Fe2+2.1 x 101414.33Fe3+1.3 x 102525.1Co2+2.0 x 101616.31V3+7.9 x 102525.9Ni2+4.2 x 101818.62Th4+1.6 x 102323.2

Titrasi Kompleksometri EDTA(H4Y)

Untuk Mn+ + Y4- MYn-4 KMY = [MYn-4]/[Mn+][[Y4-] Perlu diketahui [Y4-], yang nilainya bergantung pada pHKebergantungan pH dari Y4-:Tentukan terlebih dahulu: a4 = [Y4-]/CTCT = [Y4-] + [HY3-] + [H2Y2-] + [H3Y-] + [H4Y]Konstanta pembentukan konditional, KMY[MYn-4]/[Mn+][[a4CT] = KMY KMY = a4 KMY = [MYn-4]/[Mn+][[CT]

Titrasi Kompleksometri EDTA(H4Y)Menghitung konsentrasi ion logam bebas:Gunakan konstanta pembentukan kondisional, KMYa4 bergantung pada pHSehingga, KMY valid untuk pH tertentu sajaa4 yang telah dihitung vs pH

a4 = (K1K2K3K4) / ([H+]4 + K1[H+]3 + K1K2[H+]2 + K1K2K3[H+] + K1K2K3K4)

Fraksi spesi EDTA sebagai fungsi pH. Y4- complexes with metal ions, and so the complexation equilibria are very pH dependent. Only the strongest complexes form in acid solution, e.g., HgY2-; CaY2- forms in alkaline solution.

Efek pH pada nilai Kf untuk kelat EDTA. Kf = conditional formation constant = Kfa4. It is used at a fixed pH for equilibrium calculations (but varies with pH since a4 does).

Misal: 50.0 mL 0.0500M EDTA ditambahkan ke dalam 50.0 mL 0.030M Ni2+ pada pH 3,0. Hitung [Ni2+] pada kesetimbangan.

Soal: 50.0 mL 0.010M Ni2+ dititrasi dengan EDTA 0,01 M pada pH 5,0. Hitung [Ni2+] pada saat penambahan EDTA sebanyak: 0, 5, 10, 20, 30, 40, 45, 50, 55, 60, 70 mL. Ubah [Ni2+] tersebut menjadi pNiBuat kurva pNi (sumbu y) vs Vol. EDTA (sumbu x)

Titrasi Kompleksometri EDTA(H4Y)Misal: EDTA berlebih ditambahkan ke dalam larutan Ni2+ pada pH 3.0.50.0 mL 0.0500M EDTA ditambahkan ke dalam 50.0 mL 0.030M Ni2+. Hitung [Ni2+] pada kesetimbangan. Asumsikan sangat sedikit Ni2+ yang tidak terkompleksasi:C(NiY2-) = [NiY2-] = 50.0 mL x 0.030M/100.0mL = 0.015MC(EDTA) = ((50.0 x 0.050) (50.0 x 0.030))/100.0 = 0.010 MKMY = a4KMY = [NiY2-]/[Ni2+][0.010] =0.015/[Ni2+][0.010]KMY = 4.2 x 1018; a4 = 2.5 x 10-11 @ pH = 3.0[Ni2+] = 1.4 x 10-8M

Titrasi Kompleksometri EDTA(H4Y)Kurva titrasi: pM vs volume EDTAConditional Formation Constant, KMY for specific pHe.g., 50.0mL 0.020M Ca2+ with 0.050M EDTA, pH 10.0at pH 10.0, K(CaY2-) = (a4)(KCaY) = (0.35)(5.0 x 1010) = 1.75 x 1010(a) pCa values before the equivalence point (10.0mL) Ca2+ + Y4- CaY2-assume: [CaY2-] = added EDTA dissociated chelate [Ca2+] = unreacted Ca2+ + dissociated chelateDissociated chelate = CT

Titrasi Kompleksometri EDTA(H4Y)Titration curve is: pM vs EDTA volumeConditional Formation Constant, KMY for specific pHe.g., 50.0mL 0.020M Ca2+ with 0.050M EDTA, pH 10.0at pH 10.0, K(CaY2-) = (a4)(KCaY) = (0.35)(5.0 x 1010) = 1.75 x 1010(b) pCa value at the equivalence point (20.0mL)assume: [CaY2-] = added EDTA dissociated chelate [Ca2+] = dissociated chelate = CT

Titrasi Kompleksometri EDTA(H4Y)Titration curve is: pM vs EDTA volumeConditional Formation Constant, KMY for specific pHe.g., 50.0mL 0.020M Ca2+ with 0.050M EDTA, pH 10.0at pH 10.0, K(CaY2-) = (a4)(KCaY) = (0.35)(5.0 x 1010) = 1.75 x 1010(c) pCa value after the equivalence point (25.0mL)assume: [CaY2-] = stoichiometric amount [Ca2+] CT = [excess EDTA] + [Ca2+] [excess EDTA]CT = ((25.0 x 0.050)-(50.0 x 0.020))/(75.0) = 0.0033M [CaY2-] = ((50.0mL x 0.020M)/(75.0mL))-[Ca2+] 0.0133M K(CaY2-) = [CaY2-] / [Ca2+] [CT]; [Ca2+] = (0.0133)/(0.0033)(K(CaY2-))[Ca2+] = 2.30 x 10-10 pCa = 9.64 at 25.0mL EDTANote: assumption ([Ca2+]

Kurva titrasi 100 mL 0.1 M Ca2+ versus 0.1 M Na2EDTA pada pH 7 dan 10. As the pH increases, the equilibrium shifts to the right.

pH minimum untuk titrasi efektif berbagai ion logam dengan EDTAThe points represent the pH at which the conditional formation constant, Kf', for each metal is 106, needed for a sharp end point.

The concentration of a solution of EDTA was determined by standardizing against a solution of Ca2+ prepared from the primary standard CaCO3. A 0.4071-g sample of CaCO3 was transferred to a 500-mL volumetric flask, dissolved using a minimum of 6 M HCl, and diluted to volume. A 50.00-mL portion of this solution was transferred into a 250-mL Erlenmeyer flask and the pH adjusted by adding 5 mL of a pH 10 NH3NH4Cl buffer containing a small amount of Mg2+EDTA. After adding calmagite as a visual indicator, the solution was titrated with the EDTA, requiring 42.63 mL to reach the end point. Report the molar concentration of the titrant.

Quiz

An alloy of chromel containing Ni, Fe, and Cr was analyzed by a complexation titration using EDTA as the titrant. A 0.7176-g sample of the alloy was dissolved in HNO3 and diluted to 250 mL in a volumetric flask. A 50.00-mL aliquot of the sample, treated with pyrophosphate to mask the Fe and Cr, required 26.14 mL of 0.05831 M EDTA to reach the murexide end point. A second 50.00-mL aliquot was treated with hexamethylenetetramine to mask the Cr. Titrating with 0.05831 M EDTA required 35.43 mL to reach the murexide end point. Finally, a third 50.00-mL aliquot was treated with 50.00 mL of 0.05831 M EDTA, and back titrated to the murexide end point with 6.21 mL of 0.06316 M Cu2+. Report the weight percents of Ni, Fe, and Cr in the alloy.Quiz

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