A standard solution with a FeSCN2+ concentration of 1.55x10^-4M has a percent transmittance (%T) of 18.8%. Another solution of unknown FeSCN2+ concentration has a percent transmittance of 44.8%.
A) Calculate the absorbance (A) of each solution.
B) Using the absorbances calculated in 1a, calculate the FeSCN2+ concentration of the unknown solution.
A = log 1/T
Use A1 = kc1. Substitute A1 and c1 and solve for k.
Then A2 = kc2. Substitue A2 and k and solve for c2.
A) To calculate the absorbance (A) of each solution, we can use the formula:
A = -log (%T/100)
For the first solution:
%T = 18.8%
A = -log (18.8/100)
A = 0.726
For the second solution:
%T = 44.8%
A = -log (44.8/100)
A = 0.347
B) To calculate the FeSCN2+ concentration of the unknown solution using the absorbances, we can use the Beer-Lambert Law:
A = εlc
Where:
A is the absorbance
ε is the molar absorptivity (also known as the molar absorptivity coefficient)
l is the path length of the cuvette (usually in cm)
c is the concentration in Molarity
Given that the molar absorptivity (ε) is constant and the path length (l) is the same for both solutions, we can set up an equation using the absorbances to find the unknown concentration:
A₁ = εlC₁ (equation for the first solution)
A₂ = εlC₂ (equation for the second solution)
Dividing the two equations:
A₂/A₁ = C₂/C₁
Plugging in the values:
0.347/0.726 = C₂/1.55x10^-4
Now, solve for C₂:
C₂ = (0.347/0.726) x (1.55x10^-4)
C₂ ≈ 7.41x10^-5M
Therefore, the FeSCN2+ concentration of the unknown solution is approximately 7.41x10^-5 M.