Five reddish-brown solid samples were produced by oxidizing elemental iron under…
CHEMISTRY · Multi-part · A Level · Chemistry · Amount of substance · Amount of substance
Problem
Five reddish-brown solid samples were produced by oxidizing elemental iron under different temperature and oxygen conditions. The masses of iron and oxygen in each sample are provided below.
Sample A: 7.84 g Fe and 3.36 g O
Sample B: 5.60 g Fe and 2.40 g O
Sample C: 6.72 g Fe and 2.88 g O
Sample D: 3.92 g Fe and 1.68 g O
Sample E: 7.00 g Fe and 3.50 g O
(The atomic masses to be used are: Fe = 55.85 g·mol⁻¹, O = 16.00 g·mol⁻¹.)
(a) Compute the mass ratio Fe : O for each sample, reporting each ratio to three significant figures.
(b) Group the samples into sets that can be considered the same compound based on the calculated ratios, and clearly identify any sample that represents a different compound.
(c) Explain, with reference to atomic composition, why differing Fe : O mass ratios necessitate that the solids are distinct compounds rather than impure samples of the same compound.
(d) For one of the compound groups identified in part (b) that displays a Fe : O mass ratio of approximately 2.33 : 1, derive the empirical formula of the compound. Show all molar calculations.