Question & Answer: The absorbance of a standard solution of 2.032 times 10^-4 M FeSCN^+2 (aq) was determined…..

Question #: 18 The absorbance of a standard solution of 2.032 x 104 M FeSCN*2 (aq) was determined to be 1.086. A student prepared a solution containing 4.98 mL of 0.00200 M Fe(NO) and 3.97 mL of 0.00200 M KSCN in 1.00 mL water. What is the concentration of FeSCN*2 if its absorbance at equilibrium was measured to be 0.792? A. 6.75 x104 M B. 6.81 × 10-2 M C. 2.03 × 10-4 M D. 1.48 x 104M

The absorbance of a standard solution of 2.032 times 10^-4 M FeSCN^+2 (aq) was determined to be 1.086. A student prepared a solution containing 4.98 mL of 0.00200 M Fe(NO_3)_3 and 3.97 mL of 0.00200 M KSCN in 1.00 mL water. What is the concentration of FeSCN^+2 if its absorbance at equilibrium was measured to be 0.792? A. 6.75 times 10^4 M B. 6.81 times 10^-2 M C. 2.03 times 10^-4 M D. 1.48 times 10^-4 M

Expert Answer

use formula for absorbance:

A = e*l*c

where:

A is Absorbance

e is molar absorptivity constant

l is length of cell

c is concentration = 0.100 mM = 1.00*10^-4 M

So,

A2/A1 = (c2/c1)

0.792/1.086 = c2 / (2.032*10^-4)

c2 = 1.48*10^-4 M

Answer: D

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