The ionization of p-nitrophenol is shown below (pKa = 7.0): a. Identify the weak acid and conjugate base. b. At pH 7, what are the relative concentrations of ionized and un-ionized p-nitrophenol? c. If enough concentrated hydrochloric acid is added to a solution of p-nitrophenol to lower the pH from 7 to 5, what will happen to the relative concentrations of the ionized and un-ionized forms? d. Ionized p-nitrophenol has a yellow color, while the un-ionized form is colorless. The yellow color can be measured using a spectrophotometer at 400nm. In order to determine the total amount of p-nitrophenol in a solution, would you perform the spectrophotometer reading at an acidic or basic pH? Clearly explain why? e. A solution of p-nitrophenol at pH 7.95 was found to have an A400 of 0.255 . What is the total concentration (in µM) of p-nitrophenol (ionized plus un-ionized) in the solution? The molar extinction coefficient of p-nitrophenol is 18,500 M-1cm-1 and the pKa is 7.
The ionization of p-nitrophenol is shown below (pKa = 7.0):
a. Identify the weak acid and conjugate base.
b. At pH 7, what are the relative concentrations of ionized and un-ionized p-nitrophenol?
c. If enough concentrated hydrochloric acid is added to a solution of p-nitrophenol to lower the pH from 7 to 5, what will happen to the relative concentrations of the ionized and un-ionized forms?
d. Ionized p-nitrophenol has a yellow color, while the un-ionized form is colorless. The yellow color can be measured using a spectrophotometer at 400nm. In order to determine the total amount of p-nitrophenol in a solution, would you perform the spectrophotometer reading at an acidic or basic pH? Clearly explain why?
e. A solution of p-nitrophenol at pH 7.95 was found to have an A400 of 0.255 . What is the total concentration (in µM) of p-nitrophenol (ionized plus un-ionized) in the solution? The molar extinction coefficient of p-nitrophenol is 18,500 M-1cm-1 and the pKa is 7.
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