Xg of ethylamine is subjected to reaction with NaNO₂ / HCl followed by water; evolved dinitrogen gas which occupied 2.24 L volume at STP. X is _________ × 10⁻¹ g.

Solution

Chemistry ma’am · 4 steps

One amine gives one N₂, so moles of gas tell you moles of ethylamine directly.

1. The reaction. Nitrous acid, made from NaNO₂ and HCl, turns a primary aliphatic amine into an alcohol and releases nitrogen gas. Each molecule of amine gives exactly one molecule of N₂.

   C₂H₅NH₂ + HNO₂ → C₂H₅OH + N₂ ↑ + H₂O

2. Moles of gas. At STP one mole of gas occupies 22.4 L, so 2.24/22.4 = 0.1 mol of N₂. By the 1 : 1 ratio, 0.1 mol of ethylamine reacted.
3. Mass of amine. The molar mass of C₂H₅NH₂ is 24 + 7 + 14 = 45 g mol⁻¹. So X = 0.1 × 45 = 4.5 g.
4. So. 4.5 g = 45 × 10⁻¹ g, and the answer is 45.

The common slip: 4.5. Writing the mass in grams instead of in units of 10⁻¹ g gives 4.5, not 45.

The idea to keep. A primary aliphatic amine with HNO₂ gives one N₂ per -NH₂ group. Convert the gas volume to moles and you have the moles of amine.

Answer from the NTA final answer key. Solution by PrepWiser.