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🧪AP Chemistry
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🧪AP Chemistry

FRQs 1–3 – Long Answer
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Unit 1: Atomic Structure and Properties
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Each FRQ type tests specific skills taught in particular units. Here's why certain units appear for each question type:

This mapping reflects College Board's exam structure - each FRQ type tests specific skills that are taught in particular units.

Practice FRQ 1 of 351/35

1. Answer the following questions about calcium and its compounds.

A mass spectrum for a naturally occurring sample of calcium is shown in Figure 1. The sample contains several isotopes, with calcium-40 being the most abundant.

Figure 1. Mass spectrum of a naturally occurring calcium sample (relative abundance by isotope mass number)

Figure 1
A.
i.

Based on the information in Figure 1, determine the number of neutrons in the most abundant isotope of calcium.

ii.

Calculate the approximate average atomic mass of the calcium sample using the data provided in Figure 1. Assume the abundance of Ca-40 is 97% and Ca-44 is 3%, and ignore other trace isotopes.

The complete photoelectron spectrum for calcium is shown in Figure 2.

Figure 2. Photoelectron spectrum (PES) of calcium (peak height proportional to number of electrons in each subshell)

Figure 2
B.
i.

Based on the photoelectron spectrum in Figure 2, write the ground-state electron configuration for calcium.

ii.

Identify the peak in Figure 2 that corresponds to the electrons in the 2p sublevel. Explain why this peak is approximately three times taller than the peak corresponding to the 2s sublevel.

A student analyzes a pure sample of a calcium chloride compound to determine its empirical formula. The student determines that a 2.77 g sample of the compound contains 1.00 g of calcium.

C.

Calculate the empirical formula of the calcium chloride compound using the data provided (2.77 g sample containing 1.00 g Ca).

In a separate experiment, the student is given a 4.50 g mixture containing solid CaCl₂ and solid SiO₂ (sand). The student adds water to dissolve the CaCl₂, filters the mixture to collect the solid SiO₂, and dries the solid. The final mass of the dry SiO₂ is 1.35 g.

D.

Calculate the mass percent of CaCl₂ in the original 4.50 g mixture.

E.

Answer the following questions regarding periodic trends.

i.

Explain why the atomic radius of calcium is larger than the atomic radius of magnesium.

ii.

Explain why the first ionization energy of calcium is greater than the first ionization energy of potassium.

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Free Response Question Practice

This practice environment simulates the AP AP Chemistry Free Response Questions section. Here are some guidelines:

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Tip: Answer all parts of each question. Partial credit is often available, so even if you are unsure, provide what you know.