The standard solution of FeSCN2+ (prepared by combining 9.00 mL of 0.200 M Fe(NO3)3 w/1.00 mL of 0.0020 M KSCN) has an absorbance of 0.500. If a trial's absorbance is measured to be 0.310 and its initial concentration of SCN– was 0.0010 M, the equilibrium concentration of SCN– will be
To find the equilibrium concentration of SCN–, we can use the Beer-Lambert law, which relates the absorbance of a solution to its concentration. The law is represented by the equation A = εbc, where A is the absorbance, ε is the molar absorptivity, b is the path length of the cuvette, and c is the concentration of the absorbing species.
In this case, we are given the absorbance of the standard solution (A = 0.500). We can use this information along with the known concentrations of Fe(NO3)3 (0.200 M) and KSCN (0.0020 M) to determine the molar absorptivity (ε).
Using the equation A = εbc, we rearrange it to solve for ε:
ε = A / (bc)
Given:
A = 0.500
b = unknown (path length is not provided)
c = unknown (concentration of SCN– at equilibrium)
Since the path length is not provided, we cannot directly calculate the molar absorptivity (ε). However, for the purpose of this explanation, let's assume the path length is 1 cm.
ε = 0.500 / (1 * c)
ε = 0.500 / c
Now, let's move on to the trial with an absorbance of 0.310 and an initial concentration of SCN– of 0.0010 M.
Using the same equation A = εbc and rearranging it to solve for c:
c = A / (εb)
Substituting the given values:
c = 0.310 / (0.500 / (0.0010 * 1))
c = 0.310 / (0.500 / 0.0010)
c = 0.310 / 0.000002
c = 1.55 * 10^5 M
Therefore, the equilibrium concentration of SCN– will be approximately 1.55 * 10^5 M.