Spectrophotometer Problems: Convert Transmittance to Absorbance: 25.5%______ 0.5

Question

Spectrophotometer Problems: Convert Transmittance to Absorbance: 25.5%______ 0.567______ 32.8%_____ 3.58%_____ 0.085_____ 53.8%______ A solution containing 4.48ppm KMnO4 has a Transmittance of 0.309 in a 1.0cm cuvette at 520nm. Calculate MOLAR ABSORPTIVITY. Ans:_____ A solution containing a Bismuth complex has a Molar Absorptivity of 9320 L/Mole/cm at 470 nm; the Molar concentration of the Bismuth complex is 6.24 times 10-5 M. The path length is 1.0 cm. Calculate the ABSORBANCE: Ans.______ 0.10 mM KMnO_4 has an absorbance maximum of 0.26 near 525 nm in a 1.000 cm cell. Find the concentration of a solution whose absorbance is 0.52 at 525 nm in the same cell.

Explanation / Answer

a) To convert a value from percent transmittance (%T) to absorbance, use the following equation:

Absorbance = 2 – log(%T)

ie..

1) 2-log(25.5%)=2-1.748= 0.2519 units.

2) 2-log(32.8%)=2-1.5158= 0.4842 units

3) 2-log(3.58%)= 2-0.5538=1.4462 units

4) 2-log(53.8%)=2-1.7307= 0.2693 units.

Absorbance = 2 – log(%T)

A=0.567=27.10%

A= 0.085=82.22%

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