CHEMISTRY · Multi-part · A Level · Chemistry · Amount of substance · Amount of substance
Problem
A gaseous organic compound contains only carbon, hydrogen, and a single halogen X. Careful mass-percent analysis gives the following composition by mass:
• Carbon: 6.91 %
• Hydrogen: 1.15 %
• Halogen X: 91.94 %
Natural samples of the elemental halogen X consist of two stable isotopes, ⁷⁹X and ⁸¹X.
(1) Determine the empirical formula of the compound from the mass-percent data. Show all intermediate mole calculations.
(2) Using the empirical formula and the composition data, calculate the average atomic mass of X to two significant figures.
(3) Identify element X by comparison with periodic-table values, and explain your reasoning.
(4) Given that the only stable isotopes of X are ⁷⁹X and ⁸¹X, calculate the percent abundance of each isotope that is consistent with the average atomic mass you obtained.