Question

pq - 30. a molecular compound is found to consist of 30.4% nitrogen and 69.6% oxygen. if the molecule contains 2 atoms of nitrogen, what is the molar mass of the molecule? (a) 46 g·mol⁻¹ (b) 92 g·mol⁻¹ (c) 154 g·mol⁻¹ (d) 168 g·mol⁻¹

Explanation:

Step1: Determine mass of nitrogen in the molecule

Let the molar mass of the molecule be $M$. The mass - percentage of nitrogen is 30.4%. Since the molecule contains 2 atoms of nitrogen, and the molar mass of nitrogen ($N$) is $14\ g/mol$, the mass of nitrogen in the molecule is $2\times14 = 28\ g$. We know that the mass of nitrogen in the molecule can also be expressed as $0.304M$.

Step2: Solve for molar mass $M$

Set up the equation $0.304M=28$. Then $M=\frac{28}{0.304}\approx92\ g/mol$.

Answer:

B. $92\ g\cdot mol^{-1}$