🧪AP Chemistry
3. Answer the following questions about calcium and its compounds.
Calcium is an alkaline earth metal that occurs naturally in various minerals. The mass spectrum of a sample of naturally occurring calcium is shown in Figure 1.
Figure 1. Mass spectrum of naturally occurring calcium (relative abundance vs. mass-to-charge ratio, m/z)
Based on the mass spectrum in Figure 1, identify the mass number of the most abundant isotope of calcium.
Calculate the number of neutrons in an atom of the isotope identified in part (A)(i).
A student analyzes a 5.000 g sample of an impure mixture containing calcium carbonate, CaCO3(s), and inert impurities. The student heats the sample to decompose the CaCO3(s) into solid calcium oxide, CaO(s), and carbon dioxide gas, CO2(g). The data from the experiment are recorded in Table 1.
Equation 1
CaCO₃(s) → CaO(s) + CO₂(g)
Table 1. Gravimetric analysis data
Measurement | Mass (g) |
|---|---|
Mass of empty crucible | 22.000 |
Mass of crucible + sample mixture before heating | 27.000 |
Mass of crucible + solid residue after heating | 25.240 |
Use the data in Table 1 to answer the following questions.
Calculate the number of moles of CO₂(g) produced during the decomposition. Assume that the decomposition of CaCO₃(s) was complete.
Calculate the mass percent of CaCO₃(s) in the original 5.000 g mixture.
Write the complete ground-state electron configuration for a neutral calcium atom.
Write the complete ground-state electron configuration for a calcium ion, Ca²⁺.
Figure 2. Photoelectron spectrum (PES) of calcium: relative number of electrons vs. binding energy (log scale, decreasing to the right)
The photoelectron spectrum of calcium is shown in Figure 2.
Identify the peak in Figure 2 that corresponds to the electrons in the 3p sublevel. Justify your answer in terms of the relative number of electrons.
The binding energy of the 4s electrons in calcium is 0.59 MJ/mol. The binding energy of the 4s electrons in potassium is 0.42 MJ/mol. Explain why the binding energy of the 4s electrons in calcium is higher.
Explain why the atomic radius of calcium is larger than the atomic radius of magnesium.
Lattice energy is the energy required to separate one mole of an ionic solid into its gaseous ions.
Predict whether the lattice energy of CaO(s) is greater than, less than, or equal to the lattice energy of K₂O(s).
Justify your answer to part (F)(i) in terms of Coulomb's law.
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