A student uses Job\'s Method to analyze several samples of [Fe(SCN)n]^+3-n and p
ID: 516619 • Letter: A
Question
A student uses Job's Method to analyze several samples of [Fe(SCN)n]^+3-n and plot their absorbances on a graph of Absorbance vs. Mole Fraction of Ligand. The resulting equations are: y = 1.2550x + 0.0707 and y = -1.2550x +1.3377. Determine the overall mol fraction of each ion, the n value, and the empirical formula of the iron complex. (Since you aren't given the data table from which to determine the proper limitations on the slopes and y-intercepts, use these equations as they are given, without first changing the significant figures of the slopes or digits of precision of the y-intercepts. Follow all other applicable significant figure rules.) Equation Setup: X_SCN: X_FE: n: Empirical Formula:_Explanation / Answer
The two equations are:
y = 1.2550x + 0.0707
y = -1.2550x + 1.3377
Therefore,
1.2550x + 0.0707 = -1.2550x + 1.3377
===> 1.2550x + 1.2550x = 1.3377 – 0.0707
===> 2.51x = 1.267
===> x = 1.267/2.51 = 0.505 0.50
x gives the mole fraction of the ligand in the complex. The mole fraction of the ligand in the complex is 0.5 which indicates that 50% of the reactants making up the complex is the ligand. Since the ligand contains only Fe3+ and SCN-, the remaining 50% of the complex must be the metal ion. Therefore, the complex contains 50% metal ion and 50% ligand. Since the ligand is monodendate, the co-ordination number of the metal is n = 1 (since one metal ion will bind with one ligand ion to form the complex having 50:50 metal:ligand ratio).
The empirical formula of the complex is [Fe(SCN)n]+3-n = [Fe(SCN)1]+3-1 [Fe(SCN)2+].
Ans: The mole fraction of the ligand and the metal ion in the complex are 0.5 each.
The co-ordination number of the metal in the complex is 1.
The empirical formula of the complex is [Fe(SCN)]2+.
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