Experiment 3

# Experiment 3 - Experiment 2 Spectrophotometric...

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Experiment 2: Spectrophotometric Determination of Acidity Constant “A” Questions 1) What quantity is the spectrophotometric analysis measuring? A spectrophotometer measures the intensity of light as a function of the wavelength of light. The spectrophotometer measures the absorbance (A) by measuring the amount of light absorbed when the light is shined through the sample. 2) Show how the value of the Ka for the m-nitroaniline maybe derived from this quantity A = log (I O ÷ I) pka = -log [H + ] [B] [BH + ] 3) Define the quantities and units of “absorbance” and “molar absorption coefficient”. 4) A solution containing 4.48ppm KMnO 4 has a transmittance of 0.309 in 1.00cm cell at 520nm. Calculate the molar absorption coefficient of KMnO 4 . At wt of KMnO4 = 158.036 158.036 × 100 = 158036ppm Therefore 1M of KMnO 4 is 158036ppm If 1M → 158036ppm Then 4M → xppm 4.48ppm = 2.834797 × 10 -5 M Now A = -log 10 T = εCl = -log 10 (0.309)

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= 0.51004152 Therefore εCl = 0.51004152 ε =
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Experiment 3 - Experiment 2 Spectrophotometric...

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