For one of the solutions you make up for this week\'s experiment, 7.00 mL of 2.0
ID: 596150 • Letter: F
Question
For one of the solutions you make up for this week's experiment, 7.00 mL of 2.0E-3 M iron(III) nitrate solution is mixed with 2.00 mL of 2.0E-3 M potassium thiocyanate solution, 3.00 mL of 0.500 M nitric acid solution, and 8.00 mL of distilled water for a total volume of 20.00 mL. What is the initial concentration of Fe3+ ions in this solution, in other words, what is the concentration of Fe3+ ions before any reaction with the thiocyanate?Initial concentration of Fe3+ =
Calculate the mole fractions of Fe3+ and SCN- in this solution with respect to the total number of moles of Fe3+ and SCN-. This means, of course, that these two mole fractions should add up to 1.00.
Mole fraction of Fe3+ = ????
Mole fraction of SCN- = ????
Suppose that the mole fraction of Fe3+ in the iron(II) - thiocyanate solution was plotted against the absorbance of the solution at 450 nm. Suppose also that the maximum absorbance was established at a mole fraction of Fe3+ equal to 0.400 by plotting the two best straight lines through the data points. What is the stoichiometry of the complex formed between the Fe3+ and the thiocyanate?
Enter the answer as a whole number ratio; whole numbers separated by a colon (for example, 2:3, indicating a stoichiometry Fe2(SCN)3).
Stoichiometry of the complex formed between Fe3+ and SCN- = ????
Explanation / Answer
0.007L x 0.002M Fe(NO3)2 = 1.4x10^-5 moles Fe3+ in Fe(NO3)3
moles Fe3+ / total volume of the solution = molarity of Fe 3+
1.4x10^-5moles Fe3+ / 0.02L = 7x10^-4M Fe3+ present
mole fraction Fe3+ = moles Fe3+ / total moles present
moles SCN- = 0.002L x 2x10^-3M = 0.4x10^-5moles SCN-
1.4x10^-5moles Fe3+ / (1.4x10^-5 + 0.4x10^-5) = 0.778
mole fraction SCN- = 0.222
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