126. Solving a chemistry problem

32. The content of phenol in water was determined by coulometric titration. To do this, we took a 100 ml sample to be analyzed, placed it in a coulometric cell, added acid, potassium bromide (in excess compared to the presumably required amount for the reaction with phenol), and conducted a chronometric titration of phenol with electrogenerated bromine at a constant current I = 30 mA. To complete the reaction
С6Н5ОН ЗВг2 = Вг3С6Н2ОН ЗНВг
it took 8 min 20 s.
Calculate the phenol content (µg/ml) in the analyzed water if the molar mass of phenol is 94.117 g/mol.
Answer: 24.4 mcg / ml.