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24 Organic and Biological Chemistry Solutions to Exercises The formula weight of is 72, so the molecular formula is also C₄H₈O. Since the compound has a carbonyl group and cannot be oxidized to an acid, the only possibility is 2-butanone. The boiling point of 2-butanone is 79.6°C, confirming the identification. 24.98 Determine the empirical formula, molar mass, and thus molecular formula of the compound. Confirm with physical data. 1 mol C = 7.136 mol C; 7.136/7.136 = 1 = 14.19 mol H; 14.19/7.136 ≈ 2 Empirical formula is Using Equation 10.11 (MM = molar mass): MM = = (735/760) atm The molecular formula is thus C₅H₁₀. The absence of reaction with aqueous Br₂ indicates that the compound is not an alkene, so the compound is probably the cycloalkane cyclopentane. According to the Handbook of Chemistry and Physics, the boiling point of cyclopentane is 49°C at 760 torr. This confirms the identity of the unknown. 24.99 The reaction is: 2NH₂CH₂COOH(aq) = (-488) + (-237.13) - 2(-369) = 12.87 = 13 kJ 24.100 (a) At low pH, the amine and carboxyl At high pH, the amine and carboxyl groups are protonated. groups are deprotonated. OH CH₂ C C OH OH CH₂ C H H o o (b) OH(aq) CH₃C + = 1.8 10⁻⁵, = -log(1.8 = 4.74 The conjugate acid of NH₃ is + 746