In an Ostwald-process plant, 120 mol of NH3 is converted completely to NO by air over a Pt-Rh catalyst. All the NO is oxidised to NO2, which is absorbed completely in water by 3NO2 + H2O -> 2HNO3 + NO. The NO released in this last step is NOT recycled. Taking the molar mass of HNO3 as 63 g mol^-1, the mass of nitric acid obtained is

JEE Advanced levelSingle correct optionDifficulty 3 of 3pn030

In an Ostwald-process plant, $120$ mol of $NH X_{3}$ is converted completely to $NO$ by air over a Pt-Rh catalyst. All the $NO$ is oxidised to $NO X_{2}$ , which is absorbed completely in water by $3 NO X_{2} + H X_{2} O 2 HNO X_{3} + NO$ . The $NO$ released in this last step is NOT recycled. Taking the molar mass of $HNO X_{3}$ as $63 g mo l^{- 1}$ , the mass of nitric acid obtained is

Each mole of

NH X_{3}

gives 1 mol

NO

and then 1 mol

NO X_{2}

. Absorption converts 3 mol

NO X_{2}

into 2 mol

HNO X_{3}

, so

HNO X_{3}

120 \times \frac{2}{3} = 80.0

mol. Mass =

80.0 \times 63 = 5040 g = 5.04 kg

(full recycling would instead give 7.56 kg).