Visual colorimetry by transmission or reflection

Visual colorimetry, used for more than four centuries, is a simplified form of instrumental absorption spectrometry. Given its modest cost and its frequently surprising precision it is therefore widely practised. 

For this purpose, these tubes were placed over a source of white light, to be observed in transmission. These selective tests, ready to use and requiring no instrumentation, complement established methods and by their rapidity help to extend the range of semi-quantitative analyses. 

1 Calculate the energy of a mole of photons corresponding to a wavelength of 300 nm. 

2 Calculate the absorbance of an organic dye (C = 7 x 10 mol L ), knowing that the molar absorptivity s = 650 mol cm and that the length of the optical path of the cell used is 2 x 10 m. What would happen to the absorbance if the cell used was of double its present thickness  

Calculate the molar absorptivity coefficient for the permanganate at this wavelength. 

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