Neco 2020 Chemistry Question 43

An industrial wastewater contains phenol at a concentration of 150 mg L⁻¹. The water is treated in two successive stages. Stage 1 is a biological degradation that removes 60 % of the phenol. Stage 2 is an advanced oxidation (Fenton's reagent) that removes 80 % of the phenol remaining after Stage 1. (a) Determine the phenol concentration after the two stages. (b) The oxidation reaction follows the stoichiometry \(\text{C}_6\text{H}_5\text{OH} + \text{H}_2\text{O}_2 \rightarrow \text{C}_6\text{H}_5\text{OOH} + \text{H}_2\text{O}\) (1:1 molar ratio). The molar masses are \(M_{\text{phenol}} = 94.11 \text{ g mol}^{-1}\) and \(M_{\text{H}_2\text{O}_2}=34.01 \text{ g mol}^{-1}\). If the wastewater flow rate is 2000 L h⁻¹, calculate the mass of hydrogen peroxide required per hour for Stage 2, assuming 100 % reaction efficiency.