DETERMINATION OF SOLUBILITY PRODUC fordssolving me in a satura lished, so You wi
ID: 999502 • Letter: D
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DETERMINATION OF SOLUBILITY PRODUC fordssolving me in a satura lished, so You will experimentally determine the K and Determination of the K" requires the equilibrium of Pblz. We need a solution in which a dynamic s a saturated solution of Pblz in contact with ex stoichiometry of the dissolution process allows us to determine only one um molartg insoluble Pbla in water ty equilibrium has been established, so ANT, Ksp, OF LEAD(U IODIDE solution with excess solid Pbl2 will be used. Using te only one of thested, Uging the e of the two, You will oxidize the iodide ion in the saturated Pbla solution to elemental iodined n be measure using on in a slightly acidic medium. The absorbance of the iodine in the solution using a spectrophotometer. A second solution containing a be treated with acidified KNO2. The absorbing species is the same for the sa solution and the known KI solution. Using Beer's Law, A ebc, the known will be known concentration of from the KI (aq). and the absorbance of the b from the known solution, we can ca ori can he , re calculated molar'a the known solution, we ca n-1 of r will also species is the same for the saturated Pblz can calculate the . molar absorptivity, e, for l2. The calculated molar absorptivity and the absorba the unknown solution can be used to calculate the equilibrium concentration of l2. e, of l2 from in the diluted unknown solution. t Do not add the potassium nitrite solution until you have access to a spectrophotometer. Once the l2 is formed, it escapes from the solution over time. So absorbance measure be taken soon after the reaction is complete. ments should The [2] we calculated is the concentration of the diluted solution. We added KNO2 solution and Hl solution to convert the I into l2 We must determine the concentration of r in the original Pbl2 solution. It is necessary to work backwards from the measured [I2] in the diluted solution to the [I] in the original saturated Pbl2 solution. Using the original concentration of iodide ion, Ul. before the dilution, we can calculate the concentration of lead(I) ion, [Pb1 Kap can be calculated using [Pb2] and [IU]. The ionic strength of the solution can be calculated since we know the major concentrations of ions in the solution. The activity coefficient, Ox and the activity of each ion, ax. can be calculated providing the necessary components to calculate Ksp The thermodynamic equilibrium constant can be compared to an accepted value from Lange's Handbook. PRELAB QUESTIONS 1. Write the half reaction for the oxidation of iodide ion. 2. A student started with 3.00 mL of 4.56 x 103 M KI solution. To this solution, she added 3.00 mL of 0.02 M KNO2 and 0.900 mL of 1 M HCI. Calculate the initial concentration of I in the diluted solution. 3. Write the chemical equation for the dissolving of lead(l) iodide. 4. Give the equilibrium expression for the solubility product of lead(l) iodide. 5. If the equilibrium concentration of iodide ion, [lea, in Pbl2 solution equals 2.40 x 103 M what is the equilibrium concentration for lead(I) ion? OLUBILITY PRODUCT EXP. NOTES 139Explanation / Answer
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PbI2(s) <--------> Pb+2 (aq)+ 2I- (aq)
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Ksp = [Pb+2][I-]2
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For every lead iodide that dissolves one lead ion and 2 iodide ions.
Therefore [Pb+2]= 1.2 * 10-3 and [I-]=2.4*10-3
Keq = [Pb+2][I-]2 /[PbI2]
since the activity of solid is taken as 1 unity Keq = Ksp = 6.9 x 10-9
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2KI + 2KNO2 + 4HCl -----------> 4KCl + 2NO + I2 + 2H2O
M1V1/n1 = M2V2/n2
4.56*10-3 *3 = M2 *6.9
M2 (intial concn of I-) = 0.00198260869M
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