i need to figure out [FeNCS 2+ ], equilibrium, from Calibration Curve (mol/L) fo

Question

i need to figure out [FeNCS2+], equilibrium, from
Calibration Curve (mol/L) for all test solutions

Molar Concentration of Fe(NO3)3 (mol/L) 0.002 (~0.002 M) Molar Concentration of NaSCN (mol/L) 0.002 (~0.002 M) Test Solutions 6 7 8 9 10 Volume of Fe(NO3)3 (mL) 5.00 5.00 5.00 5.00 5.00 Moles of Fe3+, initial (mol) 1.00E-05 1.00E-05 1.00E-05 1.00E-05 1.00E-05 Volume of NaSCN (mL) 1.00 2.00 3.00 4.00 5.00 Moles of SCN-, initial (mol) 2.00E-06 4.00E-06 6.00E-06 8.00E-06 1.00E-05 Percent Transmittance, %T 86.1 65.9 45.9 41.1 33.1 Absorbance, A 0.065 0.181 0.338 0.386 0.48 Calculculation of Kc [FeNCS2+], equilibrium, from
Calibration Curve (mol/L) Moles FeNCS2+, at equilibrium (10 mL) (mol) 3.53E-07 0.00E+00 0.00E+00 0.00E+00 0.00E+00

Explanation / Answer

For the reaction, Fe3+ + SCN- -----------> FeSCN2+

Kc= [FeNCS]2+/[Fe3+][SCN-]

From the absorbance values, you can determine the concentration of [FeNCS2+] at equlibrium

A= ab[FeNCS]2+

where,

a is molar absorptivity

b is path length

[FeNCS]2+ = A/ab

Therefore,

Kc = (A/ab)/[Fe3+]ini[SCN-]ini

However, you need to find out what is the exact concentartion [Fe3+] and [SCN-] at equlibrium.

we know that [Fe3+]ini = [Fe3+]+[FeSCN2+] (ini- means initial concentration)

Therefore, [Fe3+] = [Fe3+]ini - [FeSCN2+] =  [Fe3+]ini -(A/ab)

Similarly for [SCN-]

[SCN-]= [SCN-]ini-(A/ab)

So,

Keq = (A/ab)/{[[Fe3+]ini-(A/ab)][[SCN-]ini-(A/ab)]

Related Questions

Navigate

• Browse (All)
• Browse I
• Subjects

---

---

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