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# Analytical Chem, note set 4 2154

Virginia Tech

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This 2 page Class Notes was uploaded by Thomas Salazar on Sunday October 2, 2016. The Class Notes belongs to 2154 at Virginia Polytechnic Institute and State University taught by Dr. Amanda Morris in Fall 2016. Since its upload, it has received 20 views. For similar materials see Majors Analytical Chemistry in Chemistry at Virginia Polytechnic Institute and State University.

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Date Created: 10/02/16

Note Set #4 – week 6 Analytical Chemistry PRECIPITATION TITRATIONS The solubility constant of a rxn. (K )sps the inverse of the formation constant (K) of fhe back reaction of a metal-ion complex. Titration curve/regions of titration o Before precipitation: x+ y- n Ksp = [M ][C ] , where M is the metal cation, and C is the counter ion, and n is the coefficient of the counter ion in the balanced rxn. equation. Calculate moles of each species, use C V =C1V 1o f2nd2equivalence pt. (Ve) Calculate how much counter ion is left after the rxn. goes to completion *remember stoichiometry of the balanced eqn.!!!* Solve for new concentration of counter ion using the total volume, plug into Ksp equation, and solve for M , [M ], and pM x+ o Equilibrium: Use mass balance to set up a system of equations to solve at equilibrium Use systematic treatment to algebraically set up the Ksp equation in x+ x+ terms of [M ] as the only variable. Solve algebraically for [M ]. Solve for pM x+ o Excess/post equilibrium: Calculate moles of each species, use C V =C1V 1o f2nd2equivalence pt. (Ve) Calculate how much metal ion is left after the rxn. goes to completion *remember stoichiometry of the balanced eqn.!!!* Calculate [M ] by using the total volume, solve for pM x+ EDTA TITRATIONS *EDTA is treated as if it react with a metal ion in a 1:1 ratio **Any form of EDTA will react, and in titrations the pH is always fixed ???? ????+ + ???? 4− ↔ ???????? ????−4 [ ????−4] General eqn. for EDTA titration: Kf= ???????? where the numerator is the [????????+][????4−]???? concentration of metal-EDTA complexed, [M ] is the concentration of free metal in solution, [EDTA] is the conc. of uncomplexed EDTA in soln., and α is the fractional coefficient of EDTA at a given pH. o By using α as a constant, we can move it to the left side of the eqn. to correct ′ 4− the formation constant to???? , ????nd assume that the [???? ] = [EDTA], giving the following corrected eqn. ′ ???????? ????−4] ′ ????????= ???? ????+]???????????????? ] where ???? ???? ???? (α???? Note Set #4 – week 6 Analytical Chemistry Titration curve/regions of titration: curve plots p[M ] vs. Volume ETDA added o Before equilibrium: Calculate moles of each species, use C V =C 1 1o fi2d2equivalence pt. (Ve) Calculate how much free metal ion is left after the rxn. Goes to completion *remember the ratio of {metal : EDTA} is always 1:1 regardless of charge* Solve for new concentration of metal ion using the total volume, solve n+ for p[M ] o At equilibrium: use C 1 =1 V 2o 2ind equivalence pt. (V ) e at equilibrium, ???????? ????−4] = ([M ]+initial ???????? ) ???????????????????????? at equilibrium, [M ] = [EDTA]; plug into ???? equation using ???????? [ ????−4 ] ???? from the previous step above, c o After equilibrium: ???? After equilibrium find ???????? ????−4 ]= ([M ]+ initial ???? ) using the new V total ???????????????????????? Calculate [EDTA] finalhe same way, but substitute the initial ???????????????????? −???????? concentration of EDTA: ???????????????? ]final([EDTA] initial???? ) ′ n+ ???????????????????? n+ Plug values into ???? e????uation and solve for [M ]. Calculate p[M ]. ELECTROCHEMISTRY Gibbs Free Energy: ΔG = ΔH – TΔS (units in kJ, kJ/mol, K, and J/K) o ΔH: change in enthalpy of rxn. o ΔS: change in entropy of rxn. 1 Joule = 1 Volt•1 Coulomb ΔS = S products S reactants o T: temperature in Kelvin Work (W) = ΔE • q where “ΔE” is change in electric potential in volts (V) and “q” is charge in Coulombs (C) o q = nF where “n” is moles of electrons and “F” is Faraday Constant: 96,485 C/mol e o Therefore; W = nFΔE o Also, W = -ΔG; so ΔG = -nFΔE Power (P) o Measured in (watts): 1 watt = 1 Joule/sec ???? P = (ΔE • q) / sec ΔE ΔE • I Power = Voltage x Current ???????????? P = ΔE • I

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