1. You placed your dirty fingerprints on the cuvet while determining the %T for
ID: 701671 • Letter: 1
Question
1. You placed your dirty fingerprints on the cuvet while determining the %T for the test solutions. Explain why this error in technique results in the moles of Fe compound being reported as too high per 100 g of 2. (a) If one of the test solutions in Part B.3 is diluted with too much water, will the %T of the solution be too high or too low? (b) How will this affect the reported moles of Fe" per 100 g of compound? 3. If the cuvet used for the measurement of 96T for Standard Solution 3 in Part A.3 is not properly rinsed of Standard Solution 2, will the 96T for Standard Solution 3 be too high or too low? Explain. 4. In Parts A.2 or 8.1, if the solution is too acidic, the tris-bipyridyliron(I1) complex will not form Considering the properties of ligands in general, why might the bipyridyi ligand will not bond to the iron(lI) in the acidic solution? 5. In the determination of the formula Kw,Fe,(C20aly(H20), the stoichiometric point was surpassed in determining the oxalate ion concentration using permanganate ion as the titrant. If the iron(Ill) concentration was determined accurately, how will the error affect the value of w in the formula?Explanation / Answer
(1) It is said that dirty fingerprints are placed on the cuvette which contaminates the surface of it resulting in an error. The contaminant found is Fe3+ (ferric ions).
The common source of ferric ion is from rust. This might be the case where you touched a rusted iron and with the same, touched the cuvette during which your fingerprint deposited some ferric ions on the surface of the cuvette.
Thus, the ferric ions got added up during transmittance test which resulted in it being too high.
(2.a) When the solution is diluted, the concentration becomes low. Concentration and transmittance are inversely proportional to each other, so the %T of the solution will be too high.
(2.b) The moles of Fe3+ ions per 100 g of the compound will naturally decrease on high dilution.
(3) This question refers to a value from a previous question which is not given.
Nonetheless, when the cuvette is not rinsed properly the solution becomes contaminated by the previous solution. As we know that transmittance is inversely proportional to concentration. When a solution of lower concentration is mixed with a solution of higher concentration, the net concentration is always in the range of lower to higher.
Suppose, if the %T of solution 2 is higher than the original %T value of solution 3, then %T of solution 3 will be more as compared to the original value because the net concentration of solution 3 will decrease and transmittance will increase.
Again, suppose if the %T of solution 2 is lower than the original %T value of solution 3, then %T of solution 3 will be less than the original value of solution 3 because the net concentration of solution 3 will increase and transmittance will decrease.
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