AP Chemistry Unit 1 Practice Test & Exam | 21 Questions

1. [Skill: 2.A | Topic: 1.1] A student transfers a piece of aluminum metal into a dry beaker and records a mass of 12.0 g Al. Assume the aluminum is pure. Which of the following is the best estimate of the number of Al atoms in the sample? (Molar mass of Al = 26.98 g/mol; $N_A = 6.022\times 10^{23}\ \text{mol}^{-1}$.)

(A)$2.68\times 10^{23}$ atoms(B)$4.46\times 10^{24}$ atoms(C)$1.11\times 10^{23}$ atoms(D)$7.24\times 10^{24}$ atoms

2. [Skill: 2.A | Topic: 1.1] A lab technician prepares two sealed containers at the same temperature and pressure. Container 1: 10.0 g Ne(g) Container 2: 10.0 g Ar(g) Which of the following best compares the number of atoms in Container 1 to the number of atoms in Container 2? (Molar masses: Ne = 20.18 g/mol, Ar = 39.95 g/mol.)

(A)Container 1 has about 0.50 times as many atoms as Container 2.(B)Container 1 has about 2.0 times as many atoms as Container 2.(C)Container 1 has about the same number of atoms as Container 2 because the masses are equal.(D)Container 1 has about 4.0 times as many atoms as Container 2.

3. [Skill: 2.A | Topic: 1.1] A sample of ammonium sulfate, $(NH_4)_2SO_4$, has a mass of 5.00 g. Assume the sample is pure. Which of the following is closest to the number of formula units of $(NH_4)_2SO_4$ in the sample? ($N_A = 6.022\times 10^{23}\ \text{mol}^{-1}$.)

(A)$2.28\times 10^{22}$ formula units(B)$4.56\times 10^{22}$ formula units(C)$2.28\times 10^{23}$ formula units(D)$5.70\times 10^{21}$ formula units

4. [Skill: 5.A | Topic: 1.2] A sample of element X is analyzed using mass spectrometry. The results are shown below. | Peak (m/z) | Relative abundance (%) | |---|---| | 34.0 | 75.0 | | 36.0 | 25.0 | Based on the mass spectrum, what is the best estimate of the average atomic mass of element X?

(A)34.0 amu(B)34.5 amu(C)35.0 amu(D)36.0 amu

Refer to the figure below.

5. [Skill: 3.B | Topic: 1.2] A mass spectrum of element Q shows three distinct peaks at m/z = 20.0, 21.0, and 22.0. The peak at 20.0 is much taller than the other two, and the peak at 22.0 is taller than the peak at 21.0. Which of the following conclusions is best supported by the mass spectrum data?

(A)Element Q has three isotopes, and the isotope with mass 20.0 amu has the greatest natural abundance.(B)Element Q has three isotopes, and the isotope with mass 21.0 amu has the greatest natural abundance.(C)Element Q has an average atomic mass of exactly 21.0 amu because there are three peaks.(D)Element Q must have an average atomic mass closer to 22.0 amu because 22.0 amu is the largest mass present.

6. [Skill: 1.B | Topic: 1.2] Element Z has two naturally occurring isotopes: Z-63 with isotopic mass 62.93 amu and abundance 69.0%, and Z-65 with isotopic mass 64.93 amu and abundance 31.0%. Which mass spectrum best represents a sample of element Z?

(A)Two peaks of equal height at m/z = 62.93 and m/z = 64.93(B)Two peaks with the taller peak at m/z = 62.93 and the shorter peak at m/z = 64.93(C)Two peaks with the taller peak at m/z = 64.93 and the shorter peak at m/z = 62.93(D)One peak at m/z = 63.00 because the average atomic mass is between 62.93 and 64.93

7. [Skill: 2.A | Topic: 1.3] A student analyzes a pure compound containing only iron (Fe) and oxygen (O). The student determines that a 2.487 g sample contains 1.740 g Fe and 0.747 g O. Assuming the compound contains only Fe and O, which of the following is the empirical formula of the compound? (Use molar masses: Fe = 55.85 g/mol, O = 16.00 g/mol.)

(A)FeO(B)FeO2(C)Fe2O3(D)Fe3O4

8. [Skill: 2.A | Topic: 1.3] A pure compound is found to have the following percent composition by mass: 40.0% C, 6.7% H, and 53.3% O. Which of the following is the empirical formula of the compound? (Use molar masses: C = 12.01 g/mol, H = 1.008 g/mol, O = 16.00 g/mol.)

(A)CH2O(B)C2H4O2(C)CH2O2(D)C2H2O

9. [Skill: 4.A | Topic: 1.3] A compound X is known to contain only elements A and B. Two different students collect samples labeled as compound X and determine the masses of each element in their samples. Student 1: 2.00 g A and 3.00 g B Student 2: 4.00 g A and 5.50 g B Which of the following best explains whether both samples can be pure samples of the same compound X?

(A)Yes; both samples can be pure because they contain the same two elements.(B)Yes; both samples can be pure because both samples have more mass of B than A.(C)No; if both samples were pure compound X, the mass ratio B:A would be the same in both samples, but it is not.(D)No; pure compounds must contain equal masses of each element.

10. [Skill: 2.A | Topic: 1.4] A student analyzes a 10.00 g solid mixture that contains only sodium chloride, $NaCl$, and potassium chloride, $KCl$. Elemental analysis shows that the mixture contains 5.50 g of chlorine, $Cl$. Based on the data, what is the mass percent of $NaCl$ in the mixture?

(A)22.3%(B)43.2%(C)56.8%(D)77.7%

11. [Skill: 1.A | Topic: 1.4] Two samples are prepared in separate beakers. • Sample 1: A measured amount of sugar is stirred into water until the liquid is clear. The appearance is uniform throughout. • Sample 2: A measured amount of sand is stirred into water. After standing, some of the solid settles to the bottom. Which statement correctly identifies Sample 1 and Sample 2?

(A)Sample 1 is a pure substance; Sample 2 is a homogeneous mixture.(B)Sample 1 is a homogeneous mixture; Sample 2 is a heterogeneous mixture.(C)Sample 1 is a heterogeneous mixture; Sample 2 is a homogeneous mixture.(D)Sample 1 is a pure substance; Sample 2 is a pure substance.

12. [Skill: 4.A | Topic: 1.4] A student is given a white powder that is claimed to be pure calcium carbonate, $CaCO_3(s)$. An elemental analysis of the powder shows it is 35.0% calcium by mass. The molar mass of $CaCO_3$ is 100.09 g/mol. (Atomic masses: Ca = 40.08 g/mol, C = 12.01 g/mol, O = 16.00 g/mol.) Which conclusion is best supported by the data?

(A)The sample is pure $CaCO_3$ because 35.0% Ca is close to the theoretical percent of Ca in $CaCO_3$.(B)The sample is pure $CaCO_3$ because elemental analysis cannot be used to assess purity.(C)The sample is not pure $CaCO_3$ because the theoretical percent Ca in $CaCO_3$ is about 40.0%, which differs significantly from 35.0%.(D)The sample must contain an impurity that increases the calcium mass percent above the theoretical value for $CaCO_3$.

13. [Skill: 2A | Topic: 1.5] A student measures successive ionization energies for an unknown element X. Ionization energies (kJ/mol): IE_1 = 578 IE_2 = 1817 IE_3 = 2745 IE_4 = 11580 Based on the data, which of the following is the correct ground-state electron configuration for X and for X^{3+}? (Assume X is a neutral atom in its ground state before ionization.)

(A)X: 1s^2 2s^2 2p^6 3s^2 3p^1 ; X^{3+}: 1s^2 2s^2 2p^6(B)X: 1s^2 2s^2 2p^6 3s^2 3p^3 ; X^{3+}: 1s^2 2s^2 2p^6 3s^2(C)X: 1s^2 2s^2 2p^6 3s^2 ; X^{3+}: 1s^2 2s^2 2p^5(D)X: 1s^2 2s^2 2p^6 3s^1 ; X^{3+}: 1s^2 2s^2 2p^6

Refer to the figure below.

14. [Skill: 1B | Topic: 1.5] [Image Cue]: Line graph, "First Ionization Energy Across Period 3", x-axis: element (Na, Mg, Al, Si), y-axis: first ionization energy (kJ/mol). Data points: Na 496, Mg 738, Al 578, Si 786. Key trend: increase from Na to Mg, drop at Al, increase to Si. The graph shows first ionization energies for several period 3 elements. Which statement best explains why the first ionization energy of Al is lower than that of Mg?

(A)Al has a larger atomic radius than Mg, so its valence electron experiences less Coulombic attraction to the nucleus because it is, on average, farther away.(B)The first electron removed from Al is a 3p electron, which is higher in energy and less penetrating (more shielded) than the 3s electron removed from Mg, so it is easier to remove.(C)Al has fewer protons than Mg, so Al’s nucleus exerts a weaker attractive force on electrons in the n = 3 shell.(D)Al has a filled 3p subshell, which makes it unusually stable and therefore easier to ionize than Mg.

Refer to the figure below.

15. **1.** [Skill: 2.A | Topic: 1.6] A photoelectron spectrum (PES) is collected for a gaseous sample of element $M$. In PES, peak position corresponds to the binding energy of electrons in a subshell, and peak height is proportional to the number of electrons in that subshell. The spectrum shows five distinct peaks with relative heights of approximately 2 : 2 : 6 : 2 : 1, from highest binding energy to lowest binding energy. Which of the following is the ground-state electron configuration of element $M$?

(A)1s² 2s² 2p⁶ 3s² 3p¹(B)1s² 2s² 2p⁶ 3s² 3p²(C)1s² 2s² 2p⁶ 3s¹(D)1s² 2s² 2p⁶ 3s²

16. **2.** [Skill: 4.A | Topic: 1.6] Two photoelectron spectra are collected under the same experimental conditions for gaseous atoms of sodium (Na) and magnesium (Mg). The Mg spectrum has peaks corresponding to the same core subshells as Na (1s, 2s, 2p), and each of those corresponding peaks occurs at a higher binding energy in Mg than in Na. In addition, the lowest-binding-energy peak in Mg is approximately twice as tall as the lowest-binding-energy peak in Na. Which of the following best explains these observations?

(A)Mg has a greater nuclear charge than Na, and because both atoms have the same core electron shielding, the valence and core electrons in Mg experience a greater attraction to the nucleus, resulting in higher binding energies; Mg also has 2 electrons in the 3s subshell compared with 1 in Na.(B)Mg has more electron shielding than Na, so electrons in Mg are less attracted to the nucleus, resulting in lower binding energies; the taller peak occurs because Mg has more subshells than Na.(C)Na has a greater nuclear charge than Mg, so electrons in Na are held more tightly, resulting in higher binding energies; the taller peak in Mg occurs because Mg has more protons.(D)The binding energies are higher in Mg because Mg has a larger atomic radius than Na, so its electrons are farther from the nucleus and require more energy to remove; the taller peak occurs because Mg has 1 valence electron.

Refer to the figure below.

17. **1.** [Skill: 4.A | Topic: 1.7] A student constructs a graph of **first ionization energy** for the elements in **Period 2**. [Image Cue]: Line graph, "First Ionization Energy Across Period 2", x-axis = "Element (Li, Be, B, C, N, O, F, Ne)", y-axis = "First ionization energy (kJ/mol)". The curve generally increases from Li to Ne, with a noticeable **drop from Be to B** and another **drop from N to O**. Which of the following best identifies the cause of the **drop from Be to B**? (A) Boron has a larger atomic radius than beryllium, so its valence electron experiences less attraction to the nucleus. (B) Boron’s first electron removed is from a 2p orbital, which is higher in energy and more shielded than Be’s 2s electron. (C) Boron has fewer protons than beryllium, so its nucleus attracts electrons less strongly. (D) Boron has a filled valence shell that makes its electron harder to remove than Be’s electron.

(A)Boron has a larger atomic radius than beryllium, so its valence electron experiences less attraction to the nucleus.(B)Boron’s first electron removed is from a 2p orbital, which is higher in energy and more shielded than Be’s 2s electron.(C)Boron has fewer protons than beryllium, so its nucleus attracts electrons less strongly.(D)Boron has a filled valence shell that makes its electron harder to remove than Be’s electron.

18. **2.** [Skill: 6.A | Topic: 1.7] A student is missing data for bromine (Br) and wants to **estimate** its atomic properties using periodic trends. The student has the following reference data: - Chlorine (Cl): atomic radius = 99 pm; electronegativity = 3.16 - Iodine (I): atomic radius = 133 pm; electronegativity = 2.66 All three elements are in Group 17. Which of the following predictions for bromine (Br) is most consistent with periodic trends and Coulombic reasoning? (A) Br has an atomic radius between 99 pm and 133 pm, and an electronegativity between 3.16 and 2.66. (B) Br has an atomic radius less than 99 pm, and an electronegativity less than 2.66. (C) Br has an atomic radius greater than 133 pm, and an electronegativity greater than 3.16. (D) Br has an atomic radius between 99 pm and 133 pm, and an electronegativity greater than 3.16.

(A)Br has an atomic radius between 99 pm and 133 pm, and an electronegativity between 3.16 and 2.66.(B)Br has an atomic radius less than 99 pm, and an electronegativity less than 2.66.(C)Br has an atomic radius greater than 133 pm, and an electronegativity greater than 3.16.(D)Br has an atomic radius between 99 pm and 133 pm, and an electronegativity greater than 3.16.

19. **1. [Skill: 2.A | Topic: 1.8]** A student investigates the relative reactivity of several Group 1 metals by placing equal-sized pieces of each metal into separate beakers containing room-temperature water. The student records the observations shown. - Li(s): slow bubbling; metal remains intact after 2 min - Na(s): vigorous bubbling; metal quickly disappears - K(s): very vigorous bubbling; a flame is observed Which of the following best explains the trend in reactivity observed for Group 1 metals in water?

(A)Down the group, the valence electron is farther from the nucleus and experiences less Coulombic attraction, making it easier to lose; therefore reactivity increases.(B)Down the group, the number of valence electrons increases, so the metals are more reactive with water.(C)Down the group, the nuclear charge increases, so the nucleus attracts the valence electron more strongly and the metals react more quickly.(D)Down the group, the metals have higher melting points, so they react more quickly with water.

20. **2. [Skill: 2.B | Topic: 1.8]** A chemist knows that magnesium forms the ionic compound magnesium oxide, $MgO(s)$, when it reacts with oxygen. Based on periodic trends, which of the following is the most likely formula for the ionic compound formed between calcium and oxygen?

(A)$CaO$(B)$Ca_2O$(C)$CaO_2$(D)$Ca_2O_3$

AP Chemistry Unit 1: Atomic Structure and Properties Practice Exam

Exam Details

A. Multiple-Choice Questions (20 Questions)

B. Short Answer Questions (1 Question)

AP Chemistry Unit 1: Atomic Structure and Properties Practice Exam

Exam Details

A. Multiple-Choice Questions (20 Questions)

B. Short Answer Questions (1 Question)