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AP Chemistry Unit 4.1: Evidence of Changes

Practice AP Chemistry Unit 4.1 questions on using observable evidence such as phase, mixtures, gas formation, precipitates, heat, light, and color to classify changes.

Syllabus
Effective Fall 2025
Course
AP Chemistry

Exam points

  • Use stoichiometric relationships and empirical data to determine composition, formulas, and reaction quantities.
  • Calculate masses, moles, and concentrations from balanced equations and measured experimental values.

Covered syllabus points

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

4.1 Introduction for Reactions 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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