1. Wher NaSCN solutions in this experiment, a student mistak FeNCS2 ion solution

Question

1. Wher NaSCN solutions in this experiment, a student mistak FeNCS2 ion solution be higher, lower, or unafected enly used a graduated cylinder instead of volumetric therewere fingerprints on the auvette? Briefly explain pipets. After collecting all the data, the student realized he'd used the wrong piece of equipment, but he didnt redo the experiment.Also, he later reakzed that he had consistently misread the graduated cylinder and had thus transferred volumes that were actally 5% than the recorded volumes How would the error described in 2(1) affect FeNCS2 ion concentration in the solution? Incorporate these measurement errors into the cs data for one of your equilibrium solutions, and caloulated recompute K for that solution Determine whether the Brietly explain student's measurement errors would cause each of the following, as recaloulated by you, to be higher than, lower than, or identical to the value you originally deter mined. Briefly explain (2) (1) the caloulated SCN" ion concentration in the standard solution (3) How would the error described in 2(1) affect the calaulated K? Briefly explain (2) the slope of the Beer's Law plot 3. Briefly explain why you can make the assumption that all of the SCN ion in solutions S2-S6 has been converted to FeNCS2+ ion (3) the calculated equilibrium solution concentra- tions 4. Verify the assumption described in Question 3. To do so, use your mean Kg to calculate the equilibriunm SCN ion concentration in Solution S6. The initial Fe3 ion concentration should be 4.00 × 10-2M, the initial SCN" ion concentration is recorded on Data Sheet 1 You will have to solve a quadratic equation (4) calculated K

Explanation / Answer

Question1:

1.A standard solution of SCN- was prepared by transfering a volume V (in fact 0.95V or 95% V) from the stock solution into a volumetric flask. Fe3+ was added in high excess to allow SCN- to completely react, thus the error in measuring volume for Fe3+ is not relevant.

The procedure was repeated with a series of different V volumes (C concentrations of SCN-). The actual concentrations C are actually 95% of the calculated values. A correction is possible (multiply the calculated C values by 0.95).

2.)

A series of absorbancies was recorded. A plot A vs. C is an equation:

A = sC + i      (s= slope, i= intercept).

s = (A-i)/C . If C (of SCN- and also FeSCN2+) is in fact lower, the absorbancies are (about 5%) lower and the slope is lower.

But if C are corrected at a) , the calibration curve is correct (unaffected).

3)

A new series of mixtures (Fe3+ + SCN ) was prepared with concentrations more close one to each other, e.g., [Fe3+]/[SCN-] in ratios 5:1 , 4:1, 3:1, 2:1, 1:1.

Each concentration for [Fe3+] and [SCN-] was in fact lower (95%), but the ratios were not affected. Using the wrong Beer’s Law plot

C = (A-i)/s   with a lower s, the calculated C are higher (the actual [FeESCN2+ is only 95%).

To correct the data, use the corrected slope from b).

4)

Kcorrect = [FeSCN2+]/([Fe3+][SCN-])

The initial calculation was made with

1.05[FeSCN2+]/(0.95[Fe3+]·0.95[SCN-]) = Kwrong= 1.16Kcorrect

Correct Kwrong by 1.16 or use the corrected data from a,b,c for a re-calculation.

Question2)

(1) Fingerprints or water spots or any dirt or contaminant on the walls of the cuvette would effect the path of light when such cuvette is placed in spectrophotometer and reflect and scatter the light, lessening the intensity of the transmitted light and thus would result in an error in the reading of absorbance, leading to a higher aborbance than the compound would otherwise exhibit without the fingerprint /contaminant [Note: Transmittance is iversely related to Absorbance)

so measured absorbanc eof FENCS2+ ion would be higher if finger prints are there on the cuvette

(2) Since the absorbance is higher for the ion, its concentration would be recored as higher than it otherwise should be

Absorbance is directly proportional to concentration [Beer Lambert's law]

(3)

AB ----------> A+ + B-

Ksp = [A+] [B-]

Ksp solubility product is nothing but product of concentration of the cation and anion that the compound gives

since the concentrations are reflected higher than normal, Ksp also exhibits higher value than it is supposed to be.

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