A pure, dry sample of an unknown organic compound possessing active hydrogen atoms is analyzed via Z — Hydrocarbons Chemistry Question
Question
A pure, dry sample of an unknown organic compound possessing active hydrogen atoms is analyzed via Zerewitnoff's active hydrogen determination method. If 1.79 mg of this compound (Molar Mass = 90 g/mol) reacts completely with excess $CH_3MgI$ to liberate exactly 1.34 mL of methane gas measured at standard temperature and pressure (STP), how many active hydrogen atoms does one molecule of the compound contain?
💡 Solution & Explanation
Moles of organic compound = $\frac{1.79 \times 10^{-3} \text{ g}}{90 \text{ g/mol}} \approx 1.989 \times 10^{-5}$ moles. Moles of $CH_4$ gas evolved at STP (22400 mL/mol) = $\frac{1.34 \text{ mL}}{22400 \text{ mL/mol}} \approx 5.982 \times 10^{-5}$ moles. The ratio of moles of methane to moles of compound is $\frac{5.982 \times 10^{-5}}{1.989 \times 10^{-5}} \approx 3$. Since one mole of active hydrogen reacts with one mole of Grignard to produce one mole of $CH_4$, there are 3 active hydrogens per molecule.