Correct Answer: 15

Explanation

Step 1: Correct the pressure of nitrogen gas

Observed pressure = 715 mm Aqueous tension = 15 mm

\[ P_{\text{dry}} = 715 - 15 = \mathbf{700\ mm} \]

Step 2: Convert pressure into atm

\[ P = \frac{700}{760} = \mathbf{0.921\ atm} \]

Step 3: Use ideal gas equation to find moles of nitrogen

Volume of N₂ = 70 mL = 0.070 L Temperature = 300 K Gas constant \(R = 0.0821\)

\[ n = \frac{PV}{RT} \]

\[ n = \frac{0.921 \times 0.070}{0.0821 \times 300} \]

\[ n \approx \mathbf{0.00262\ mol} \]

Step 4: Calculate mass of nitrogen

Molar mass of N₂ = 28 g mol⁻¹

\[ \text{Mass of nitrogen} = 0.00262 \times 28 \approx \mathbf{0.0734\ g} \]

Step 5: Calculate percentage of nitrogen

Mass of organic compound = 0.50 g

\[ \%\text{N} = \frac{0.0734}{0.50} \times 100 \]

\[ \%\text{N} \approx \mathbf{14.7\%} \]

Nearest integer value = 15%

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