CHEMISTRY · Multi-part · AP · Chemistry · Chemical Reactions · Chemical Reactions
Problem
An unknown white crystalline solid, labeled Sample X, is subjected to a sequence of tests to determine whether it undergoes chemical change upon heating.
Test 1 A small portion of Sample X is gently heated in a dry test tube. Condensation appears near the mouth of the tube, and a colorless gas escapes, turning moist blue litmus paper red.
Test 2 The solid residue remaining after Test 1 is dissolved in deionized water to form a clear solution. Addition of a few drops of 0.10M silver nitrate to this solution produces a bright yellow precipitate.
Test 3 The pH of the original, unheated Sample X suspended in water is measured to be 7.00.
(a) Based on the results of Test 1, write a balanced chemical equation (including phase labels) for a plausible decomposition reaction of Sample X that is consistent with all observations.
(b) Identify the gaseous product released in Test 1, citing the specific evidence that supports your identification.
(c) Explain how the formation of a yellow precipitate in Test 2 provides additional evidence that the heating of Sample X produced a new chemical substance rather than merely caused a phase change.
(d) Discuss why the neutral pH measured in Test 3 is insufficient to predict the outcome of Test 1, and explain what this reveals about the limitations of single-property characterization when determining chemical change.