1972 Ap Chemistry | Free Response Answers

Typical Prompt (1972): A solution contains Ag⁺, Pb²⁺, and Zn²⁺. Describe a procedure to separate and confirm each ion using 1M HCl, 1M H2SO4, and 1M NH3(aq). Write net ionic equations.

Question Summary:
The solubility product of ( PbF_2 ) is ( 3.7 \times 10^-8 ). Calculate:
(a) The molar solubility of ( PbF_2 ) in pure water.
(b) The molar solubility of ( PbF_2 ) in a 0.10 M ( NaF ) solution.

1972 Answer Key (Validated):

Score Rubric (1972): 5 points for part (a) – setup (2), cube root (2), units (1). 5 points for part (b) – common ion effect (2), approximation (2), final (1).

Step 1: Determine standard cell potential (E°_cell).

Step 2: Write the Nernst equation. For Zn + Cu²⁺ → Zn²⁺ + Cu: ( n = 2 ) electrons. [ E_cell = E°_cell - \frac0.0592n \log Q ] [ Q = \frac[Zn^2+][Cu^2+] = \frac0.100.0010 = 100 ] 1972 ap chemistry free response answers

Step 3: Calculate. [ E_cell = 1.10 - \frac0.05922 \log(100) ] [ \frac0.05922 = 0.0296 ] [ \log(100) = 2 ] [ E_cell = 1.10 - (0.0296 \times 2) = 1.10 - 0.0592 ] [ E_cell = 1.0408 , \textV ]

Answer (1972 style): 1.04 V (accept 1.04 to 1.05 V).

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By: AP Curriculum Historians

For decades, the Advanced Placement (AP) Chemistry exam has been the gold standard for high school college-level chemistry. While modern students focus on quantum mechanics and organic spectroscopy, the 1972 exam represents a fascinating "retro" challenge—a test built in an era of slide rules, log tables, and heavy emphasis on stoichiometry, equilibrium, and descriptive chemistry.

If you are searching for 1972 AP Chemistry free response answers, you are likely a tutor, a history buff, or a student using the legendary "Old AP Exams" for ultra-hardcore preparation. You have come to the right place. Typical Prompt (1972): A solution contains Ag⁺, Pb²⁺,

Disclaimer: The original 1972 AP Chemistry exam is copyrighted by the College Board. The following answers are provided for educational commentary and historical analysis based on declassified materials and retroactive scoring guidelines. They are not official College Board publications but are accurate to the chemistry of the era.

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These questions required multi-step calculations.

The half-reactions for the electrolysis of molten sodium chloride (NaCl) are:

Question 2

(a) Finding the Atomic Weight

(b) Volume of Hydrogen at STP

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Solve for $[H^+]$: $$ K_a = \frac[NH_3][H^+][NH_4^+] $$ $$ 5.56 \times 10^-10 = \fracx \cdot x0.10 - x $$

Since $K_a$ is very small, $x$ is negligible compared to $0.10$. $$ 5.56 \times 10^-10 \approx \fracx^20.10 $$ $$ x^2 = 5.56 \times 10^-11 $$ $$ x = [H^+] = 7.46 \times 10^-6\text M $$

Calculate $[OH^-]$: $$ [OH^-] = \fracK_w[H^+] $$ $$ [OH^-] = \frac1.0 \times 10^-147.46 \times 10^-6 $$ $$ [OH^-] \approx 1.3 \times 10^-9\text M $$

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