A researcher prepares two solid samples of silicon dioxide by different laboratory methods
CHEMISTRY · Multi-part · AP · Chemistry · Properties of Substances and Mixtures · Properties of Substances and Mixtures
Problem
A researcher prepares two solid samples of silicon dioxide by different laboratory methods.
• Sample 1 produces a set of sharp, evenly spaced peaks when analyzed by powder X-ray diffraction (XRD).
• Sample 2 produces a single broad hump with no distinct peaks in the same XRD apparatus.
Both samples contain only Si and O atoms in a 1 : 2 ratio.
Answer the following questions about the structural and macroscopic consequences of the two different solid forms of SiO₂.
(a) Classify each sample as either crystalline or amorphous. Support your answer with explicit reference to the XRD observations.
(b) Describe the fundamental difference in the spatial arrangement and motion of the SiO₂ particles in Sample 1 versus Sample 2 at the atomic scale.
(c) When each sample is heated at a constant rate, Sample 1 exhibits a sharp melting temperature near 1 710 °C, whereas Sample 2 softens gradually over a broad temperature range beginning near 1 200 °C. Explain the origin of this difference in melting behavior in terms of particle arrangement and the distribution of bond energies.
(d) Predict which sample is likely to transmit visible light more effectively. Justify your prediction by relating long-range order (or lack thereof) to interaction of light with the solid.