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 0.510. If a trial's absorbance is measured to be 0.250 and its initial concentration of SCN– was 0.00050 M, the equilibrium concentration of SCN– will be___?___
A = abc.
A is absorbance, a (which should be epsilon but I can't make epsilon on this board) is the molar absorptivity constant, b is the cell length, and c is the concn in mols/L.
You know A, b, and c (c from your last post). Calculate the constant, a.
The second solution also is A = abc.
You know A, you know a, you know b, and you can calculate c. That c, in mol/L, will tell you the equilibrium concn of the complex.
Now set up an ICE chart to determine how much of the original 0.0005 SCN is used and the amount remaining.
Post your work if you get stuck.
iam confused with the ice table could you show me because my answer .0002 is incorrect thanks.
i see what my problem is, thanks i got it.
i have a question, how did you find the length?
To determine the equilibrium concentration of SCN- in the given trial, we can use the concept of Beer-Lambert Law and the relationship between absorbance and concentration.
The Beer-Lambert Law states that the absorbance of a solution is directly proportional to the concentration of the absorbing species and the path length of the cell. Mathematically, it can be represented as:
A = ε * l * c
Where:
A = Absorbance
ε = Molar absorptivity (a constant for a given substance)
l = Path length (typically measured in centimeters)
c = Concentration of the absorbing species (in moles per liter)
In this case, we can assume that the path length is constant for both the standard solution and the trial solution, as the same cuvette or spectrophotometer is used. Therefore, the ratio of absorbances A1/A2 is directly proportional to the ratio of concentrations c1/c2.
We are given that the absorbance of the standard solution (A1) is 0.510 and the absorbance of the trial solution (A2) is 0.250. The initial concentration of SCN- in the trial solution (c1) is 0.00050 M. We need to calculate the equilibrium concentration of SCN- (c2).
Using the ratio of absorbance and concentration, we can set up the following proportion:
A1/A2 = c1/c2
Plugging in the values:
0.510/0.250 = 0.00050/c2
Simplifying further:
2.04 = 0.00050/c2
To solve for c2, we can rearrange the equation:
c2 = 0.00050 / 2.04
c2 ≈ 0.000245 M
Therefore, the equilibrium concentration of SCN- in the given trial is approximately 0.000245 M.