A laboratory demonstration involves gently heating a sample of pure naphthalene…
CHEMISTRY · Multi-part · AP · Chemistry · Chemical Reactions · Chemical Reactions
Problem
A laboratory demonstration involves gently heating a sample of pure naphthalene (mothball crystals) in a dry test tube until it completely vaporizes and then allowing the vapor to cool and recrystallize on the upper walls of the tube.
You are asked to decide whether the overall process that the naphthalene undergoes is a physical change or a chemical change. A basic laboratory kit is available that contains only the following items: a balance (±0.01 g), a thermometer that reads to the nearest 1 °C, a stopwatch, a ring stand with clamps, and safety equipment (goggles, gloves, tongs). No additional chemicals are provided.
(a) Describe one specific macroscopic observation you would expect to make if a chemical change, rather than a physical change, were occurring during the heating of the naphthalene.
(b) Using only the equipment listed, outline a step-by-step experimental procedure that would allow you to collect evidence sufficient to classify the change. Your design must indicate the measurements you would record, how often they would be recorded, and how the data would be used to reach a conclusion.
(c) Identify two variables—other than temperature—that must be controlled during your experiment, and explain how failing to control each variable could lead to an incorrect conclusion about the type of change involved.