Numerical answer
An organic compound of molar mass contains only carbon, hydrogen and nitrogen. In a Kjeldahl determination g of the compound liberates ammonia that is absorbed in mL of ; the unreacted acid needs mL of NaOH. A separate g sample on complete combustion gives g of . Taking , the number of hydrogen atoms in one molecule of the compound is ______.
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Answer: 7
Kjeldahl: acid consumed by ammonia meq, so the sample contains mmol of N (all nitrogen converted to ), i.e. g N. Combustion: mol C, i.e. g C. The sample mass is g, so hydrogen is g, i.e. mol H. Atom ratio C : H : N , giving empirical formula with mass . The molar mass equals the empirical mass, so the molecular formula is (aniline-type) and contains 7 hydrogen atoms.
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