Question

Answer is C.) 1.38 x 10^-5 but need explanation please

Following the same procedure as in Experiment 5, a calibration curve (absorbance vs II1) was prepared and determined to have a slope of 68.81 and a y-intercept of 0.004167. Next, 5.00 mL of 0.0120 M Pb(NOs)2, 3.00 mL of 0.0300 M K), and 2.00 mL of 0.200 M KNowere mixed in a centrifuge tube, producing a yellow precipitate of Pbl Again following the same procedure, the supernatant solution was transferred to a 10- mL volumetric flask and the absorbance due to I-was measured to be 0.434. How many moles of Pblaprecipitated from solution? a. 9.00 x 10- b. 6.25 x 105 c. 1.38 x 10 d. 6.00 x 105 e. 2.75 x 10-s

Answer 1

The relation ship between absorbance(A and concentration (c) is as follows: Aabc Here, a is the molar absorptivity and b is the pathlength. So, the graph between A versus c gives a straight line. y is the absorbance, m is the slope, x is concentration, and c is they intercept. Substitute, absorbance 0434 0.434-0.004167 68.81 fory, 0.004167 for c, and 68.81 for m. 0.00625 So, the concentration of PbI2 is 0.00625 M Moles of PbIconcentration x volume -0.00625 M)x (10 mL) 1 L (0.00625 mol/L)×1 10 mL× -6.25 x10-5 mol 1000 mL Therefore. the moles of PbI, is b. 6.25x10