Mole Concept and Some Basic Concepts of ChemistryhardMCQ SINGLE

Exactly of an unknown oxide of nitrogen undergoes complete decomposition to produce of gas and of gaMole Concept and Some Basic Concepts of Chemistry Chemistry Question

Question

Exactly $10\text{ mL}$ of an unknown oxide of nitrogen undergoes complete decomposition to produce $20\text{ mL}$ of $NO_2$ gas and $5\text{ mL}$ of $O_2$ gas under identical conditions of temperature and pressure. What is the molecular formula of the original nitrogen oxide?

Answer: D

💡 Solution & Explanation

Step 1: Write the general decomposition equation for an oxide of nitrogen $N_xO_y$. $N_xO_y(g) \rightarrow x NO_2(g) + \frac{y-2x}{2} O_2(g)$. Step 2: Apply Gay-Lussac's law of combining volumes. Volume of $NO_2 = 10x\text{ mL} = 20\text{ mL} \implies x = 2$. Volume of $O_2 = 10 \times \left(\frac{y-2x}{2}\right)\text{ mL} = 5\text{ mL}$. Substitute $x=2$: $10 \times \left(\frac{y-4}{2}\right) = 5 \implies 5(y-4) = 5 \implies y-4 = 1 \implies y = 5$. Step 3: The molecular formula is $N_2O_5$.

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