Assume that the Beer\'s Law plot prepared by a student exhibited a slope of 1.88

Question

Assume that the Beer's Law plot prepared by a student exhibited a slope of 1.88 Times 10^3 Abs-M^-1 The student then prepared an equilibrium mixture having initial concentrations of Fe^3+ and SCN' ions of 1.0 Times 10^-3 M each. After performing a blank correction she observed an absorbance of 0.28 for the equilibrium mixture. Estimate the equilibrium concentration of the FeSCN^2+ ion in this equilibrium mixture. Using Eq. 11, calculate the K_wq, value for this mixture. Why is it important to clean the surface of the cuvettes before performing an absorbance measurement?

Explanation / Answer

The beer law is as follow:

A = EbC

A: Absorbance

E = molar absorptivity (L/mol cm)

C = Concentration (mol/L)

b = pass length of the cubet (Usually 1 cm)

Now, according to your data, you have a slope data of 1.88x103. This is the value of Eb, assuming b = 1 cm, you already have the value of E with this.

Now with the value of absorbance obtained (0.28) and the E, just solve for C:

C = A/Eb

C = 0.28 / 1.88x103 = 1.49x10-4 M

Now to calculate Kc, we need first to write the overall reaction:

r: Fe3+ + SCN- <--------> FeSCN2+

i: 0.001 0.001 0

e: 0.001-x 0.001-x x

The value of x is the value of C calculated before = 1.49x10-4 M so Kc:

Kc = 1.49x10-4 / (0.001-1.49x10-4)2

Kc = 205.74

Hope this helps.

Related Questions

Navigate

• Browse (All)
• Browse A
• Subjects

---