1 . Why is it important to run a blank solution to set the zero %T for both Part

Question

1 . Why is it important to run a blank solution to set the zero %T for both Parts l and 11 in this experiment? How would your results be affected if you did not run a blank? The blank solution represents the ntensi the detechor fron the "bankolation. The an is he base line J ip nis noi documented wewill not measure the absorbance accurately lig ht reachin 2. Briefly explain why you can assume that the equilibrium concentration of FesCN2 ion in solutions S2- S6 is equal to the initial concentration of SCN ion in these solutions. In an acidie solution, iron(I) ion reversibly binds to thiocu anate on (SCN), Sotmina a red coovdination ion 24 1mal oS SCN-is converted to 4 n101 ?f Fe SCN-+ Thus, the assu (tion is Valid. 3 Using your average value for Keq and the concentration/absorbance data for mixture S6, verify the assumption discussed in Question 2. You may need to solve a quadratic eqation. Average Koa value = 1697,65 Concentration Fe SCN":2.0x10-ym/absorbance o.276

Explanation / Answer

Fe3+ + SCN- --> FeSCN2+

Average Keq = 1697.65

[FeSCN2+] = 2 x 10-4 M

Initial [SCN-] = 2 x 10-4

Fe3+ + SCN- --> FeSCN2+

Y + 2 x 10-4 – x --> x

Keq = [FeSCN2+] / ([SCN-] [Fe3+]) = x / ((2 x 10-4 – x) (Y)) = 1697.65

x / (2 x 10-4 – x) = 1697.65 Y

Since Fe3+ is in much excess, assuming it ~ 0.1 M

x / (2 x 10-4 – x) = 169.765

Solving we get,

x = 1.99 x 10-4 M ~ 2 x 10-4 M

Hence, the assumption is valid.

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