Question

Standard #	Volume of 0.00020 M FeCl3 (mL)	Volume of 2 M HCL (mL)
Blank	0	10.00
1	0.20	9.80
2	0.40	9.60
3	1.00	9.00
4	2.00	8.00
5	3.00	7.00

Using the table, calculate the concentration of [Fe(SCN)6]^3– in each of the standard solutions you will prepare. Show all of your work, including units, for the calculation of the concentration of standard #1. (For standards 2-5, you may simply list the concentrations with units without showing your work.)

Answer 1

You have not given the amount of SCN^- added to each solution , the volume of SCN^- added has to be considered to determine the concentration of [Fe(SCN)6]^3– in the final solution.

The reaction is:

Fe³⁺ + 6SCN^- = [Fe(SCN)₆]^3-

Let y mL of (m) molar SCN^- solution is added to each solution.

For the solution 1:

Total volume = 0.2 + 9.8 + y = 10 + y mL

Concentration of Fe³⁺ after mixing the solutions = 0.2 mL * 0.0002 M / (10 + y mL)

=[ 0.00004 /(10 + y mL)] M

According to the reaction, 1 M Fe³⁺ reacts to give 1 M [Fe(SCN)₆]^3-

So concentration of [Fe(SCN)₆]^3- in the solution =[ 0.00004 /(10 + y mL)] M

Do the same for the rest of the solutions.