(Solved): Treatment of ammonia with phenol in the presence of hypochlorite yields indophenol, a blue product ...

Treatment of ammonia with phenol in the presence of hypochlorite yields indophenol, a blue product that absrobs light at $$625\mathrm{nm}$$, which can be used for the spectrophotometric determination of ammonia. To determine the ammonia concentration in a sample of lake waterr, three samples are prepared. In sample A, 10.0 mL of lake water is mixed with $$5\mathrm{mL}$$ of phenol solution and $$2\mathrm{mL}$$ of sodium hypochlorite solution, and diluted to $$25.0\mathrm{mL}$$ in a volumetric flask. In sample B, $$10.0\mathrm{mL}$$ of lake water is mixed with $$5\mathrm{mL}$$ of phenol solution, $$2\mathrm{mL}$$ of sodium hypochlorite solution, and $$2.50\mathrm{mL}$$ of a $$5.50\times 10^{?4}\mathrm{M}$$ ammonia solution, and diluted to $$25.0\mathrm{mL}$$. Sample $$\mathrm{C}$$ is a reagent blank. It contains $$10.0\mathrm{mL}$$ of distilled water, $$5\mathrm{mL}$$ of phenol solution, and $$2\mathrm{mL}$$ of sodium hypochlorite solution, diluted to $$25.0\mathrm{mL}$$. The absorbance of the three samples is then measured at $$625\mathrm{nm}$$ in a $$1.00\mathrm{cm}$$ cuvette. The results are shown in the table. What is the molar absorptivity $$(?)$$ of the indophenol product? c) What is the concentration of ammonia in the lake water?