A 5.00 g sample containing only (NH4)2SO4 and Na2SO4 is heated with excess NaOH ((NH4)2SO4 + 2NaOH -> Na2SO4 + 2NH3 + 2H2O). It releases 0.616 L of NH3 at STP (molar volume 22.4 L/mol). Molar mass of (NH4)2SO4 is 132 g/mol. Find the mass percentage of (NH4)2SO4 in the sample, to one decimal place.

JEE Main levelNumerical answerDifficulty 2 of 3qc210

A $5.00 g$ sample containing only $(NH X_{4}) X_{2} SO X_{4}$ and $Na X_{2} SO X_{4}$ is heated with excess NaOH ( $(NH X_{4}) X_{2} SO X_{4} + 2 NaOH Na X_{2} SO X_{4} + 2 NH X_{3} + 2 H X_{2} O$ ). It releases $0.616 L$ of $NH X_{3}$ at STP (molar volume $22.4 L/mol$ ). Molar mass of $(NH X_{4}) X_{2} SO X_{4}$ is $132 g/mol$ . Find the mass percentage of $(NH X_{4}) X_{2} SO X_{4}$ in the sample, to one decimal place.

Numerical answer type, answer in %, tolerance 0.1.

Moles of

NH X_{3}

0.616/22.4 = 0.0275

. Moles of

(NH X_{4}) X_{2} SO X_{4}

0.0275/2 = 0.01375

, mass =

0.01375 \times 132 = 1.815 g

. Percentage =

1.815/5.00 \times 100 = 36.3%