Question

Solution	Volume of 0.20 M Fe3+	Volume of 0.002 M SCN-	Volume of H2O
A-1	25.0 mL	0.0 mL	75.0 mL
A-2	25.0 mL	5.0 mL	70 mL
A-3	25.0 mL	7.0 mL	68.0 mL
A-4	25.0 mL	9.0 mL	66.0 mL
A-5	25.0 mL	11.0 mL	64.0 mL

Solution	Volume of 0.002 M Fe3+	Volume of 0.002 M SCN-	Volume of H2O
B-1	5.0 mL	1.0 mL	5.0 mL
B-2	5.0 mL	2.0 mL	4.0 mL
B-3	5.0 mL	3.0 mL	3.0 mL
B-4	5.0 mL	4.0 mL	2.0 mL
B-5	5.0 mL	5.0 mL	1.0 mL

I. Calibration Curve

1. Record the absorbance for each of the standard solutions in the table below. Calculate the concentration of Fe(SCN)2+ in each of the standard solutions and record the values in the table below. Show your work in the space below the table.

Solution	Absorbance	[Fe(SCN)2+]
A-1                                           0.000
A-2                                           0.359
A-3                                           0.524
A-4                                           0.626
A-5                                           0.866
A-6                                           0.972
A-7                                           1.065

　

II. Determination of the equilibrium constant

1. Record the absorbance values for each of the equilibrium solutions in part II and calculate the [Fe(SCN)2+]eq concentration for each of the solutions using the obtained calibration curve in part I. Show your work in the space provided below.

Solution	Absorbance	[Fe(SCN)2+]eq
B-1                                         0.000
B-2                                         0.097
B-3                                         0.301
B-4                                          0.465
B-5                                          0.533

Please i need help findind the concentrations of [Fe(SCN)^2+] for part I and II. i don't need the whole chart complete just atleast 2 each and the formulas on how do them so i can do it on my own. Thanks

Answer 1

I. Calibration curve,

concentration of [FeSCN]2+ = concentration of [SCN-] in solution

A-1 [FeSCN]2+ = 0 and [SCN-] = 0

A-2 [FeSCN]2+ = 0.002 M x 5 ml/100 ml = 0.0001 M

A-3 [FeSCN]2+ = 0.002 M x 7 ml/100 ml = 0.00014 M

Similarly others can be calculated

Now from absorbance vs concentration of [FeSCN]2+ calibration plot we will get slope

Use slope for II. Determination of equilibrium constant

slope = molar absorptivity for [FeSCN]2+

II. Determination of equilibrium constant

Concentration of [FeSCN]2+ in B-1 to B-5

Concentration [FeSCN]2+ = absorbance/slope

So,

B-1 [FeSCN]2+ = 0 M

B-2 [FeSCN]2+ = 0.097/slope

B-3 [FeSCN]2+ = 0.301/slope

Similarly others can be calculated