1972 Ap Chemistry Free Response Answers Official
Problem: A 0.500-gram sample of a metal $M$ is burned in air. The resulting oxide, $M_2O_3$, weighs 0.711 grams. (a) Calculate the atomic weight of the metal $M$. (b) If the metal $M$ is reacted with excess $HCl$, what volume of $H_2$ gas at STP would be produced?
By: RetroChem Analyst
In the spring of 1972, Richard Nixon was in the White House, the Vietnam War raged on, and “America’s Top 40” featured Don McLean’s “American Pie.” But in high school gymnasiums converted into exam halls, a different kind of tension crackled. The future STEM elite were hunched over booklets labeled AP Chemistry. 1972 ap chemistry free response answers
For modern students, the 1972 free response section is a fascinating fossil. Before the era of calculators, data tables, or multiple-choice-heavy scoring, the 1972 exam was a raw, computational beast. It didn't test conceptual understanding as much as it tested mathematical endurance.
Here is a look back at what those students faced—and the answers that separated the 5s from the 1s. Problem: A 0
If you are comparing your work to a 1972 answer key, understand the scoring philosophy:
Separation Scheme:
Add hot water to the precipitate → PbCl₂ is slightly soluble in hot water; AgCl is not. Decant hot solution and cool → PbCl₂ recrystallizes (white needles). Confirm Pb²⁺ with 1M H2SO4 → white PbSO₄ precipitate.
To the remaining AgCl solid, add 1M NH3 → AgCl dissolves forming [Ag(NH3)2]⁺ complex. Add hot water to the precipitate → PbCl₂
Confirm Ag⁺: Add HNO₃ to the complex solution → brown precipitate of AgCl reforms.
To the original Zn²⁺ solution (after step 1), add NH₃ until basic → Zn(OH)₂ precipitates, then dissolves in excess NH₃ to form [Zn(NH3)4]²⁺. Confirm Zn²⁺ with K4[Fe(CN)6] → pale yellow Zn2[Fe(CN)6] precipitate.