Final answer:
To calculate the concentration of p-nitrophenol, find the number of moles using its mass and molar mass, and divide by the total volume of the solution including any added NaOH.
Step-by-step explanation:
To calculate the concentration of p-nitrophenol added, we must first determine the number of moles of p-nitrophenol present. Using the molar mass of p-nitrophenol (139 g/mol), we convert the given mass (7.20 × 10⁻⁴ g) of p-nitrophenol to moles.
Number of Moles = {Mass (g)} / {Molar Mass (g/mol)} = {7.20 × 10⁻⁴ g} / {139 g/mol}.
Once the number of moles of p-nitrophenol is known, the total volume of the solution after adding NaOH must be considered to ensure complete conversion to the yellow anion form. Assuming no significant volume change upon the addition of NaOH, the concentration of p-nitrophenol can be calculated as follows:
Concentration = {Number of Moles} / {Total Volume (L)}.