A forensic laboratory receives an airtight vial containing a pure
CHEMISTRY · Multi-part · AP · Chemistry · Atomic Structure and Properties · Atomic Structure and Properties
Problem
A forensic laboratory receives an airtight vial containing a pure, volatile organic liquid. Elemental analysis of a small aliquot reports the following mass composition: 52.2 % carbon, 13.0 % hydrogen, and 34.8 % oxygen by mass.
The research supervisor reminds the analyst that the laboratory must report a complete molecular formula, not merely an empirical formula, before the substance can be entered into the evidence database.
(a) Describe, in words, the logical sequence by which mass-composition data are converted into an empirical formula for a pure substance. Be explicit about the role that the mole concept plays in this reasoning.
(b) Identify one additional quantitative measurement (other than a second elemental analysis) that would allow the laboratory to determine the molecular formula of the liquid, and explain in detail why that measurement is sufficient.
(c) Several samples in the same evidence locker are suspected to be alcohols. Explain how knowledge of typical functional groups might assist the analyst in narrowing plausible molecular formulas once the empirical formula is known, even before further structural analysis is performed.