Socrates was killed by a dose of hemlock, which is a poisonous herb in the carrot family. In a combustion experiment, 50.05 mg of the poisonous compound in hemlock was burned in excess oxygen to give 140.8 mg of CO₂ and 54.2 mg of H₂O. In a second experiment, it was determined that the compound is composed of only carbon, hydrogen, and nitrogen and has a molar mass less than 200 g/mol. What is the molecular formula of the poisonous compound in hemlock? Respond with the sum of the C, N, and H atoms in this compound. For example, if the molecular formula were CNH₂, you would respond 4.

Question

Quizplus · Accepted Answer

First, let's calculate the number of moles of CO₂ and H₂O produced in the combustion experiment: moles of CO₂ = 140.8 mg / 44.01 g/mol = 0.003197 mol moles of H₂O = 54.2 mg / 48.06 g/mol = 0.001128 mol Next, let's use the mole ratio between the poisonous compound and the combustion products to determine the number of moles of the poisonous compound: moles of poisonous compound = moles of CO₂ / 0.003197 mol = 1 mol moles of poisonous compound = moles of H₂O / 0.001128 mol = 3 mol So the empirical formula of the poisonous compound is C1N1H3. Next, let's calculate the empirical formula mass of the compound: C = 1 x 12.01 g/mol = 12.01 g/mol N = 1 x 14.01 g/mol = 14.01 g/mol H = 3 x 1.01 g/mol = 3.03 g/mol Empirical formula mass = 29.05 g/mol Finally, since we know the molar mass of the compound is less than 200 g/mol, we can try multiplying the empirical formula by various integers to get a molar mass less than 200 g/mol: C2N2H6 (molar mass = 86.1 g/mol) C3N3H9 (molar mass = 143.2 g/mol) C4N4H12 (molar mass = 200.3 g/mol) The molecular formula must be one of these, and the only one that satisfies the molar mass constraint is C2N2H6. The sum of the C, N, and H atoms is 2+2+6 = 10, so the answer is A) 18.

Socrates Was Killed by a Dose of Hemlock, Which Is