Question

Biochemistry

4. The ionization of p-nitrophenol is shown below (pKa = 7.0): NO2 он weak acid conjugate base a. (4 points) Identify the weak acid and conjugate base. b. (4 points)At pH 7, what are the relative concentrations of ionized and un-ionized p- nitrophenol? c. (4 points)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. (4 points) 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. (8 points) A solution of p-nitrophenol at pH 8.5 was found to have an Adoo of 0.375 What is the total concentration (in uM) of p-nitrophenol (ionized plus un-ionized) in the solution? The molar extinction coefficient of p-nitrophenol is 19,500 M-'cm' and the pka is 7.

Answer 1

4. The lonization of p-nitrophenol is shown belowink. 70 NOZ weak adid conjugate base a. 4 points) Identify the weak acid and coning the solution behaves as a buffer and its pH = pka + log[conjugated b. base lacid hat are the relative concentrations of ionized and un-ionized nitrophenol At pH = pka, the ſionized] = [unionized according to Hendersen equation (4 points 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? If pH is decreased, [H+] increases and the equilibrium is shifted to right side, thus [unionised ]> [ionised form). d. (4 points) 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? to measure the concentration, we need to have all p-nitrophenol in measureable ionized form( yellow). so we need to take in basic pH so that all is ionised and can be measured. e. (8 points) A solution of p-nitrophenol at pH 8.5 was found to have an Acco of 0.375 What is the total concentration (in M) of p-nitrophenol cionized plus un-ionized) in the solution? The molar extinction coefficient of p-nitrophenol is 19.500 M om and the pka is 7