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Difficulty: MediumProperties of Matter

A technician observes several maintenance procedures being performed in an electronics repair depot. Which of the following processes represents a chemical change?

  1. A
    Melting solder wire to join two electrical conductors
  2. Tarnishing of silver electrical contacts upon exposure to airborne sulfurAnswer
  3. C
    Evaporating isopropyl alcohol solvent from a cleaned circuit board
  4. D
    Bending a copper grounding strap to fit inside an equipment chassis

Answer

Tarnishing of silver electrical contacts upon exposure to airborne sulfur
Tarnishing of silver contacts is a chemical change because silver reacts chemically with sulfur in the environment to produce silver sulfide (Ag2SAg_2S), creating a new chemical compound with distinct physical and chemical properties.

Step-by-Step Solution

1
Differentiate between physical and chemical changes in matter
A physical change alters form, shape, or state of matter without changing chemical composition, whereas a chemical change breaks or forms chemical bonds to produce one or more new substances.
Establishing the core scientific criteria allows systematic evaluation of each scenario.
2
Classify the molecular behavior in each observed procedure
Melting solder and evaporating alcohol are phase changes (solid to liquid, liquid to gas), and bending copper is mechanical deformation—all physical changes. Tarnishing involves silver atoms chemically combining with sulfur to yield silver sulfide (Ag2SAg_2S), a new substance.
Identifying which process produces a chemically distinct substance isolates the chemical change.

Key Concept

Distinction between physical changes (phase and shape changes) and chemical changes (formation of new chemical substances)
Estimated Time:45s
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Topics

Properties of Matter

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