CHEMISTRY · Multi-part · A Level · Chemistry · Amount of substance · Amount of substance
Problem
A chemist isolates a pure, white solid F that is believed to contain the elements C, H, N, and S. To verify the composition, a 0.250 g sample of F is completely combusted in excess oxygen, producing the following products that are collected and quantified:
• 0.367 g CO2
• 0.150 g H2O
• 0.114 g SO2
• All nitrogen remains as N2 gas, which is not trapped or quantified directly.
Atomic masses: C = 12.0 g mol−1, H = 1.01 g mol−1, O = 16.0 g mol−1, N = 14.0 g mol−1, S = 32.1 g mol−1
(1) Using the combustion data, calculate the number of moles of C, H, and S present in the original 0.250 g sample. Show your reasoning.
(2) By difference, determine the mass and moles of N in the original sample.
(3) Determine the empirical formula of F.
(4) Given the empirical formula and typical oxidation states of the constituent elements, evaluate whether F is more plausibly an ionic compound containing a polyatomic anion or a discrete molecular compound. Provide a reasoned argument that considers formal charge balance and plausible bonding environments.
(5) Propose one additional experimental measurement (other than combustion analysis) that would decisively distinguish between the two structural possibilities you discussed in part (d), and explain the expected results for each case.