How would you detect end point of step 2? 5.00 mL of a 100 ppm iron(II) standard

Question

How would you detect end point of step 2? 5.00 mL of a 100 ppm iron(II) standard is adjusted to pH 4.0 with an appropriate buffer and a excess of l,10-phenanthroline solution (complexing agent). The volume is made up to 100.0 mL with de-ionized water. An orange-colored complex called ferroin forms, in which each iron (II) ion is complexed with 1,10-phenanthroline groups. The transmittance of the resulting solution was 37.6 %T at 540 nm in a 1.2 cm path length cuvette. Calculate the molar absorptivity of ferroin assuming that the Fe-complex formation is complete. A 1.00 g sample of sludge is washed well and filtered; the filtrate collected and diluted to 100.0 mL. A 10.00 mL sample of this diluted filtrate is treated with the complexing agent in a manner identical to the standard iron solution above. The resuming complex gave a transmittance of 25.1 %T with the same instrument. Calculate the weight percent iron (II) m the sludge assuming that Beer's taw holds for this determination. Concentrated copper (II) solutions (in the absence of chloride ions) are blue in color, white the Cu (if)-ED7A complex is practically colorless. It is should be possible to follow a complexometric titration of this type spectrophotometrically. Suggest a wavelength at which you might successfully follow such a titration and sketch what the absorbance vs. EDIA (mL) added.

Explanation / Answer

c=100 mg/L(5/100)(1 g/1000 mg)(1 mol/55.85 g)=8.95e-5 M

A=-log(T)=-log(0.376)=0.4248

A=abc

a=1.2(8.95e-5M)/0.4248=2.58e-4

b) A1/c1=A2/c2
A2=0.6

solve for C2

C2= 1.264e-4

m=55.85*(1.264e-4)*10*100/10=0.70594 g

%m= 70.59 %

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