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AP Chemistry 4.1: Chemical and Physical Changes

Practice AP Chemistry questions on distinguishing physical from chemical changes by interpreting phase, mixtures, gas formation, precipitates, heat, light, and color evidence.

Syllabus
Effective Fall 2025
Course
AP Chemistry

Exam points

  • Explain how acid-base reactions involve proton transfer, conjugate pairs and equilibrium in aqueous solution.
  • Apply pH, pOH and equilibrium relationships to calculate concentrations and predict acid-base behavior.

4.1.A—Identify evidence of chemical and physical changes in matter question 1

[Maximum number: 1]

A student is given the task of determining the I−\mathrm{I}^{-}content of tablets that contain KI and an inert, water-soluble sugar as a filler. A tablet is dissolved in 50.0 mL of distilled water, and an excess of 0.20M Pb(NO3)2(aq)0.20 M \mathrm{~Pb}\left(\mathrm{NO}_{3}\right)_{2}(a q) is added to the solution. A yellow precipitate forms, which is then filtered, washed, and dried. The data from the experiment are shown in the table above.

Explain the purpose of drying and weighing the filter paper with the precipitate three times.

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