Deteemination of an equilibeium constarnt Semuner 2017 Pre-Laboratory Assignment
ID: 1029397 • Letter: D
Question
Deteemination of an equilibeium constarnt Semuner 2017 Pre-Laboratory Assignment NAME: DATE :- 1. Why is the experiment run at a wavelength of 447 nm? "t he experi wient ruis 24 If the percent transmittance of a solution is 82.7 what is the absorbance of that solution? 2-100 (ol 2. 2-109 (82,0.682 5 absorba nce units What is the relationship between concentration and absorbance in Part I of the experiment? 3. 4. Why is the Fe concentration so much higher than the KSCN in Part I of the experiment?Explanation / Answer
1. Yes your answer of Q1 is correct. The wavelength of 447nm is used for the colorimetry experiment because the absorbance for the Iron-thiocyanate ions is maximum at this wavelength.
2. Correctly calculated. But please note, absorbance has no units. It is dimensionless.
3. The concentration and absorbance has a linear relationship to each other which is expressed in the beer lambert's law.
A = Elc
Where A is absorbance,
E is the molar absorbtivity,
l is the path length- i.e., the path length of the cuvette in which the sample is contained.
c is the concentration of the compound in solution.
4. This experiment is carried to prepare a calibration curve for the colorimetric determination of thiocyanate ions in solution. Fe3+ ions is used in excess in solution because:
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