The absorbance of Fe-phenanthroline complex (reaction and structures shown below

Question

The absorbance of Fe-phenanthroline complex (reaction and structures shown below) is used to measure the amount of iron in foods in an upcoming experiment. Measurements of the blank solution gave an average absorbance of 0.03 and a calibration curve equation is absorbance = 11,100/Fe2+] + 0.03. A low concentration iron sample gave the following readings: 0.07, 0.06, 0.06, 0.05, 0.08, 0.06, 0.06, 0.07 and 0.08 a. What is the absorbance and sample concentration at the limit of detection of this method? (15 pts.) b. What is the concentration at the limit of quantitation? (5 pts.) 3. Fe2+ 3phen -> (phen) Fe(II) orange-red complex

Explanation / Answer

I have a doubt in question 4, but I can help you in question 5. Here's my attempt:

a) The overall reaction:

Pb(NO3)2(aq) + 2KI(aq) ----------> PbI2(s) + 2KNO3(aq)

With this we can actually write the net equation reaction:

Pb2+(aq) + 2NO3-(aq) + 2K+(aq) + 2I-(aq) -------------> PbI2(s) + 2K+(aq) + 2NO3-(aq)

Pb2+(aq) + 2I-(aq) <-------------> PbI2(s)   pKsp = 8.10 --> Ksp = 7.94x10-9

b) in 43.68 mL it reach the equivalence point, so we can apply the following expression:

M1V1 = M2V2

As 1 mol of Pb reacts with 2 moles of I, then the above expression:

M1V1 = 2M2V2

So:

M1 = 2*0.9584 * (43.68/100)

M1 = 0.8373 M

c) In this case, we need to use the following expression:

C = C * (Valiquot / Vfinal)

C = 0.9584 * (20 / 120) = 0.1597 M

I have a little doubt in part d) but I think you calculate the concentration. The pI is my doubt. Possibly is calculated as -log[I]. If that's the case, just calculate the concentration of I in the equivalence point. (final volume of 143.68 mL and do exactly as in part c) and then the -log[I].

If there's something else you need explanation or doubts, or something to be fixed, tell me in a comment.

Hope this helps

Related Questions

Navigate

• Browse (All)
• Browse T
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.