How do you complete the data chart with the attached information? Pre-Lab Exerci

Question

How do you complete the data chart with the attached information? Pre-Lab Exercise: Iron(III) ions and thiocyanate ions react according to the following equation: Fes (aq) SCN (aq) FescN2 (aq) For this reaction, a student prepares four standard solutions in which varying amounts of NasCN are used. For the reaction, o.200 M Fe(NO3)3 and o.00200 M NascN are used. The total volume of each reaction mixture is 50.0 mL. Use the information provided to help you fill in the missing values in parts b, c, and d in Table 1 below. Table 1: Concentration and Absorbance Data for Standard Solutions L Standard Solutions 1 2 4 a) Volume NascN (mu) 0.50 1.25 2.50 3.75 b) Moles SCN 1.0 x 10 2.50 x 10 c) [SCN] in 50.0 mL 2.0 x 10 1.50 x 10 d) [FescN24 1.00 x 10 e) Absorbance Procedure A. Preparation of the Correlation Plot Construct Table vin your lab notebook. Ripet 0.50, 1.25y 250, and Bins ml of0.00200 M NasCN into separate 50 ml volumetric flasks and dilute to the 50-mL mark with o.200 M FalNo solution which has been made up with 0.5 M HNO assolvent. We now have four

Explanation / Answer

From standard solutions,

calculate molar absorptivity (e) = slope

= (0.320 - 0.163)/(1 x 10^-4 - 5 x 10^-5)

= 3140 M-1.cm-1

Table

Reaction#                            1                       2

Fe3+ (ml) added                 5.0                    5.0

[Fe3+] initial                        0.2                    0.2

Fe3+ mmoles initial            1.0                    1.0

SCN- (ml)                            1.0                    2.0

[SCN-] initial                       0.002                0.002

SCN- mmol initial               0.002                0.004

[FeSCN]2+ initial                   0                       0

Equilibrium [FeSCN]2+ = absorbance/molar absorptivity

[Fe3+]eq = [Fe3+] initial - [FeSCN]2+eq

[SCN-]eq = [SCN-] initial - [FeSCN]2+eq

Kc = [FeSCN]2+eq/[Fe3+]eq.[SCN-]eq

Equilibrium

[FeSCN]2+eq                  6.68 x 10^-5     4.14 x 10^-5

Fe3+eq mmols                      0.999               0.999

[Fe3+]eq (M)                        0.9332            0.9586

SCN-eq mmols                    0.00131          0.00359

[SCN-]eq (M)                   1.31 x 10^-4     3.59 x 10^-4

Kc                                          0.546               0.120

average Kc                                      0.333

Similarly, Kc for other three reactions can be calculated.

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