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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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Practice FRQ 1 of 351/35

3. Answer the following questions about an unknown metal, M, and its compounds.

The photoelectron spectrum (PES) for an unknown metal M is shown in Figure 1.

Figure 1. Photoelectron spectrum (PES) of metal M (binding energy on a logarithmic scale, high energy at left).

Figure 1
A.
i.

Identify metal M based on the photoelectron spectrum in Figure 1.

ii.

Explain why Peak A has a significantly higher binding energy than Peak D using Coulomb's law and principles of atomic structure.

B.

Based on the identification of M as magnesium, answer the following questions involving periodic trends.

i.

Compare the atomic radius of Mg to the atomic radius of calcium, Ca. Explain the difference in terms of atomic structure.

ii.

Compare the first ionization energy of Mg to the first ionization energy of sodium, Na. Explain the difference in terms of atomic structure.

A student determines the molar mass of the carbonate of metal M, MCO₃, by heating a pure sample to decompose it according to the equation MCO3(s)→MO(s)+CO2(g)MCO_3(s) \rightarrow MO(s) + CO_2(g)MCO3​(s)→MO(s)+CO2​(g). The data collected is shown in Table 1.

Table 1. Gravimetric analysis data

Measurement

Value

Mass of empty crucible

24.000 g

Mass of crucible + MCO₃(s)

27.373 g

Mass of crucible + contents after heating

25.613 g

C.
i.

Calculate the number of moles of CO₂(g) produced during the experiment represented in Table 1.

ii.

Using the data in Table 1, calculate the molar mass of MCO₃.

D.

If the student did not heat the crucible long enough to drive off all the CO₂(g), would the calculated molar mass of MCO₃ be greater than, less than, or equal to the actual molar mass? Justify your answer.

A separate 5.00 g sample containing MCO₃ and inert impurities is analyzed. The sample yields 0.88 g of CO₂(g) upon complete decomposition.

E.

Calculate the mass percent of MCO₃ in the impure 5.00 g sample. Assume that the impurities do not react.

The mass spectrum of metal M is shown in Figure 2.

Figure 2. Mass spectrum of metal M (three isotopic peaks with stated relative abundances).

Figure 2
F.

Using the data in Figure 2, calculate the average atomic mass of metal M.

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Free Response Question Practice

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

  • Read each question carefully before responding. Pay attention to command verbs like "identify," "explain," "analyze," or "evaluate."
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