Question 18 of 21 Incorect 3 IncorrectIncoect Sapling Learning You wish to measu

Question

Question 18 of 21 Incorect 3 IncorrectIncoect Sapling Learning You wish to measure the iron content of the well water on the new property you are about to buy You prepare a reference standard Fo" solution with a onnonntration of 5 17 × 104 M You treat 100 mL of this reference with HNO, and excess KSCN to form a red complex, and dilute the reference to 550 mL. The diluted reference is placed in a cell with a 1.00 am light path. You then take 30.0 mL of the well water, treat with HNOa and excess KSCN, and dilute to 100.0 ml. This diluted sample is placed in a variable pathlength cell. The absorbance of the reference and the sample solutions match when the pathlength is 3.74 cm. What is the concentration of iron in the well water? For each solution, the zero is set with a blank 1Incorrect Number You calculated the dilution factor for the wel water incorrectly. The well water concentration should be higher than the concentration of the sample diluted for measurement Fe ll water 753x1 Jwell water M

Explanation / Answer

Fe+3 = 5.17*10^-4 M

V = 10 mL of this with excess

dilution to 55 mL

1 cm = cuvete

from this data, obtain e:

A1 = e1*l1*C1

A2 = e2*l2*C2

assume e1= e2 for the same species

A1 = A2

e1*l1*C1 = e2*l2*C2

l1*C1 = l2*C2

1*C1 = 3.74*C2

now.. obtain C1 from dilution set

C1 = 5.17*10^-4

Cdiluted = (5.17*10^-4)(10/55) = 0.000094

then

1*C1 = 3.74*C2

1*0.000094 = 3.74*C2

C2 = 0.000094/3.74

C2 = 0.00002513

this is diluted

V sample --> 100 mL

Vwell = 30 mL

Cwell * Vwell = Csample*Vsample

Cwell * 30 = 0.00002513*100

Cwell = 0.00002513*100/30

Cwell  0.000083766

Cwel = 8.37*10^-5 M

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