A mineral sample is suspected to contain two distinct crystalline phases: one is a gray
CHEMISTRY · Multi-part · AP · Chemistry · Compound Structure and Properties · Compound Structure and Properties
Problem
A mineral sample is suspected to contain two distinct crystalline phases: one is a gray, shiny material that can be drawn into thin wires; the other is a transparent, colorless solid that shatters when struck. A student mechanically separates the sample into Phase 1 (gray) and Phase 2 (colorless) and performs the following tests.
Test | Phase 1 | Phase 2
------------------------------------------------------
Electrical conductivity (solid) | High | None
Solubility in water | None | High
Electrical conductivity (aqueous solution) | Not applicable | High
Hardness | 3 | 6
(a) Use the data to assign a predominant bonding type to each phase. Provide evidence from the table to support each assignment.
(b) Both phases are ground into powders and mixed thoroughly. Predict how the composite powder will respond to a test for electrical conductivity in the solid state. Explain your reasoning.
(c) Design a step-by-step procedure to quantitatively determine the mass percentage of each phase in an unknown mixture of the two solids. Your procedure must rely on differences that arise from their bonding types.
(d) Identify a potential experimental limitation or source of error in the procedure you proposed in part (c) and suggest a method to minimize its impact.