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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 the element gallium (Ga).

Gallium is a group 13 element that is solid at room temperature but melts in the hand. It is commonly used in semiconductors.

Figure 1. Mass spectrum of gallium

Figure 1
A.

The mass spectrum of a sample of naturally occurring gallium is shown in Figure 1.

i.

Calculate the average atomic mass of gallium based on the data in Figure 1. Show your work.

ii.

Identify the difference in the atomic structure of the two isotopes represented by the peaks at 69 and 71.

Table 1. Experimental data for gallium oxide formation

Measurement

Mass (g)

Mass of empty crucible

24.500

Mass of crucible + gallium

25.750

Mass of crucible + gallium oxide product

26.180

B.

A student heats a sample of pure gallium in a crucible in the presence of excess oxygen to form a gallium oxide compound. The data collected is shown in Table 1.

i.

Calculate the number of moles of oxygen atoms in the final product.

ii.

Determine the empirical formula of the gallium oxide formed in the experiment. Show your work.

iii.

During the experiment, some of the solid gallium oxide product was spilled from the crucible before the final weighing. Would the calculated mass percent of gallium in the compound be greater than, less than, or equal to the actual mass percent? Justify your answer.

Figure 2. Photoelectron spectrum of gallium

Figure 2
C.

The photoelectron spectrum (PES) for the valence shells of gallium is shown in Figure 2.

i.

Write the complete ground-state electron configuration for the gallium atom.

ii.

Identify the peak (A, B, C, or D) in Figure 2 that corresponds to the electrons in the 3d subshell. Justify your answer based on relative peak intensity.

D.

Indium (In) is in the same group as gallium but is in period 5. Explain why the atomic radius of indium is larger than the atomic radius of gallium.

E.

The first ionization energy of gallium (579 kJ/mol) is lower than the first ionization energy of calcium (590 kJ/mol), even though gallium has a higher nuclear charge. Explain this phenomenon using principles of atomic structure.

Timed

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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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