The standard mixture you were given was prepared by mixing 18.0 mL of 0.200 M Fe(NO3)3 with 2.0 mL of 0.00200 M KSCN. Assuming that all of the SCN- reacted in this mixture, what is the final concentration of FeSCN2+ in the mixture?
This is the work from number 1:
Concentrations are as follows:
Use the value from #1 and the absorbance of the solution (recall A = 2-log %T) to determine the [FeSCN2+] in the other solutions based on their absorbances (including the ones above and below room temperature). [hint: Beer's Law says that absorbance is directly proportional to concentration]
Absorbances are as follows:
a) 2.304
b) 2.684
c) 2.41
d) 2.383
e) 2.343
f) 2.381
kscy Fe 3 3 am o .0020DM 6.200M Fe GCN) +3 Telect) (excess limiting Neagant 21 of
PROCESSING THE DATA 1. Write the Kc expression for the reaction in the Data and Calculation table. 2. Calculate the initial concentration of Fe3+, based on the dilution that results from addingKSCN solution and water to the original 0.0020 M Fe(NO3)3 solution. See Step 2 of theprocedure for the volume of each substance used in Trials 1-4. Calculate [Fe3+]i using theequation:
[Fe3+]i =
Fe(NO3)3 mLtotal mL X (0.0020 M)
This should be the same for all four test tubes. 3. Calculate the initial concentration of SCNâ, based on its dilution by Fe(NO3)3 and water:
[SCNâ]i =
KSCN mLtotal mL X (0.0020 M)
In beaker 1, [SCNâ]i = (2 mL / 100 mL)(.0020 M) = .000040 M. Calculate this for the otherthree beakers. 4. [FeSCN2+]eq is calculated using the formula:
[FeSCN2+]eq =
AeqAstd
X [FeSCN2+]std
where Aeq and Astd are the absorbance values for the equilibrium and standard solutions, respectively, and [FeSCN2+]std = (1/100)(0.0020) = 0.000020 M. Calculate [FeSCN2+]eq foreach of the four trials. 5. [Fe3+]eq: Calculate the concentration of Fe3+ at equilibrium for Trials 1-4 using the equation:
[Fe3+]eq = [Fe3+]i â [FeSCN2+]eq
6. [SCNâ]eq: Calculate the concentration of SCN- at equilibrium for Trials 1-4 using theequation:
[SCNâ]eq = [SCNâ]i â [FeSCN2+]eq
7. Calculate Kc for Trials 1-4. Be sure to show the Kc expression and the values substituted infor each of these calculations. 8. Using your four calculated Kc values, determine an average value for Kc.
