Question

8. (12 pts) Elemental mass percent compositioncan can be used to determine the identiy of an unknown substance. a The hallucinogenic drug LSD has the molecular formula C20HasN30. If the molecular mass of LSD is 323.43 g/mol, what is its mass percent 0? b. Campus security finds an unknown sample that they suspect is LSD. The unknown sample contains 74.07% 7.95% H, and 9.99% N. by mass. Keeping in mind the law of conservation of mass, determine the mass percent oxygen (% ) of the unknown sample (which only contains C, H, N. &0). c. Considering your answers to (a) and (b), could the unknown sample be LSD? Briefly support your answer. 9. (9 pts) A hydrobromic acid solution of unknown concentration is diluted by taking a 30.0-ml sample and adding enough water to make the total volume 1.00 L If the dilute solution is determined to have a concentration of 0.035 M, what is the concentration of the original solution? Name an experimental technique that could be used to verify this unknown solution concentration

Answer 1

a) Mass percent of Os Masson o x100 % Molecular mass 1mol Ox 160 g/mol x 100% 323:49 16:09 x 100% 323.49 b) = 4.95 Mars percent of 0 = 100% - 74.07% - 7.95% - 9.99% = 7.99% - c) The unknowa sample cannot be LSD. Reason! In LSD, the mass percent of o is 4.95% while et is 7.99% in thes compound. So, it is a different compound and not LSD. 9. for dilution miV, = M₂ V | Mr = final molarity or Mi = M2 V V = initial volume V2 = final volume 30.0mL = 1.17m Thus, concentration of original solution is (1.17 m [ Mi = initial inolarity 11.00 L = 1000mL - 0.035 MX1000.0mL

Experimentally, the concentration obtained can be verified by titration of the HBr solution with a suitable base such as NaOH.