Neohetramine, C16H21ON4 (285.37 g/mol) is a common antihistamine. A 0.1247 g sample containing this compound was analyzed by Kjeldahl method?

C₁₆H₂₁ON₄ + other reactants → 4NH₃ + other products
4NH₃ + 4H₃BO₃ → 4NH₄⁺H₂BO₃⁻
4NH₄⁺H₂BO₃⁻ + 4HCl → 4NH₄⁺Cl⁻ + 4H₃BO₃
According to above series of reactions, mole ratio C₁₆H₂₁ON₄ : HCl = 1 : 1

Moles of HCl used = (0.01477 mol/L) × (26.13/1000 L) = 3.8594 × 10⁻⁴ mol
Moles of C₁₆H₂₁ON₄ = (3.8594 × 10⁻⁴ mol) × (1/4) = 9.6485 × 10⁻⁵ mol
Mass of C₁₆H₂₁ON₄ = (9.6485 × 10⁻⁵ mol) × (285.37 g/mol) = 0.02753 g
Mass percentage of C₁₆H₂₁ON₄ in the sample = (0.02753/0.1247) × 100% = 22.08%

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OR:

[(0.01477 mol HCl / 1000 mL) × (26.13 mL) × (1 mol C₁₆H₂₁ON₄ / 4 mol HCl) × (285.37 g C₁₆H₂₁ON₄ / 1 mol C₁₆H₂₁ON₄) / (0.1247 g)] × 100%
= 22.08% C₁₆H₂₁ON₄

Moles HCl used = 0.02613 L X 0.01477 mol/L = 3.859X10^-4 mol HCl
Through the Kjeldahl process, each mole of nitrogen in the sample will ultimately react with 1 mol HC. So, the sample contained 3.859X10^-4 mol N

3.859X10^-4 mol N X (1 mol compound/4 mol N) X 285.37 g/mol = 0.02753 g compound

% compound in sample = (0.02753 g / 0.1247 g) X 100 = 22.08%