APCHEM Unit 1

What subatomic particles are found in the nucleus of an atom?

Protons and electrons

Protons and neutrons

Neutrons and electrons

Protons, neutrons, and electrons

Protons and neutrons

In his atomic theory, Dalton proposed that all atoms of a given element are identical. Which of the following observations provides the best evidence that the proposal is incorrect?

The dipole moment of O₃ is 0.53 debye, and the dipole moment of O₂ is 0.00 debye.

Elemental P can exist in both white and red forms.

The ionic radius of Cl^– is 0.181 nm, and the atomic radius of Cl is 0.079 nm.

The mass spectrum of Cu has a peak of 63 amu and another peak at 65 amu.

The mass spectrum of Cu has a peak of 63 amu and another peak at 65 amu

What is the connection between the amount of a sample in moles and the actual number of particles it contains?

Grams of Carbon

Atomic Mass Unit

Molar Mass

Avogadro's number

Avogadro's number

A student obtains a sample of a pure solid compound. In addition to Avogadro's number, which of the following must the student know in order to determine how many molecules are in the sample?

Mass of the sample, volume of the sample

Mass of the sample, density of the sample

Molar mass of the compound, mass of the sample

Molar mass of the compound, density of the sample

Molar mass of the compound, mass of the sample

Tartaric acid, used to give sour candies their characteristic sour taste, has an empirical formula of C₂H₃O₃ and a molar mass of 150.1 g/mol. What is the molecular formula of tartaric acid?

C₆H₉O₉

C₃H₂O₂

C₄H₆O₆

CHO

C₄H₆O₆

What is the fixed ratio of ions in the formula unit of iron oxide, Fe₂O₃?

1 Fe³⁺ : 1 O^2-

3 Fe³⁺ : 2 O^2-

5 Fe³⁺ : 6 O^2-

2 Fe³⁺ : 3 O^2-

2 Fe³⁺ : 3 O^2-

Determine the chemical formula of the mineral forsterite which contains 34.55% Mg, 19.96% Si, and 45.48% O by mass.

MgSiO

Mg₃Si₂O₆

MgSiO₃

Mg₂SiO₄

Mg₂SiO₄

In which of the following compounds is the mass ratio of chromium to oxygen closest to 1.62 to 1.00 ?

Cr₂O₃

CrO

Cr₂O

CrO₃

CrO₂

CrO₂

A sample of a pure compound is analyzed and found to contain approximately 30 percent N and 70 percent O by mass. The formula for the compound could be

N₂O₂

NO

NO₂

N₂O

NO₂

A student has two samples of NaCl, each one from a different source. Assume that the only potential contaminant in each sample is KCl. The student runs an experiment to determine the percent by mass of chlorine in each sample. From the results of this experiment alone, which of the following questions is most likely to be answered?

Which sample came from a salt mine, and which sample came from the ocean?

Which sample has the higher purity?

What is the source of the contaminants present in each of the samples?

Which sample has the higher density?

Which sample has the higher purity?

Sample	Mass of Carbon	Mass of Hydrogen
A	60. g	12 g
B	72 g	12 g
C	84 g	10. g
C	90 g	10. g

The masses of carbon and hydrogen in samples of four pure hydrocarbons are given above. The hydrocarbon in which sample has the same empirical formula as propene, C₃H₆?

Sample D

Sample C

Sample B

Sample A

Sample B

After completing an experiment to determine gravimetrically the percentage of water in a hydrate, a student reported a value of 38 percent. The correct value for the percentage of water in the hydrate is 51 percent. Which of the following is the most likely explanation for this difference?

Strong initial heating caused some of the hydrate sample to spatter out of the crucible.

The dehydrated sample absorbed moisture after heating.

Excess heating caused the dehydrated sample to decompose.

The amount of the hydrate sample used was too small.

The crucible was not heated to constant mass before use.

The dehydrated sample absorbed moisture after heating

A sample of a compound contains 3.21g of sulfur and 11.4g of fluorine. Which of the following represents the empirical formula of the compound?

SF₃

SF₂

SF₅

SF₄

SF₆

SF₆

A 54 g sample of ocean water contains 0.75 g of Na⁺ ions. What percent of the sample is salt, NaCl?

7.0 % NaCl

3.5% NaCl

0.60% NaCl

14% NaCl

3.5% NaCl

A sample of carbonate rock is a mixture of CaCO₃ and MgCO₃. The rock is analyzed in a laboratory, and the results are recorded in the table. Which columns in the table provide all the information necessary to determine the mole ratio of Ca to Mg in the rock?

1	2	3	4	5	6	7
Total mass of sample (g)	Mass of C in sample (g)	Mass of Mg in sample (g)	Mass of Ca in sample (g)	Molar mass of C (g/mol)	Molar mass of Mg (g/mol)	Molar mass of Ca (g/mol)
98.5	12.0	2.4	36.1	12.0	24.3	40.1

1, 2, 5

2, 3, 4, 5

3, 4, 6, 7

2, 5, 6

3, 4, 6, 7

Each student in a class placed a 2.00 g sample of a mixture of Cu and Al in a beaker and placed the beaker in a fume hood. The students slowly poured 15.0 mL of 15.8 M HNO₃(aq) into their beakers. The reaction between the copper in the mixture and the HNO₃(aq) is represented by the equation. The students observed that a brown gas was released from the beakers and that the solutions turned blue, indicating the formation of Cu²⁺(aq). The solutions were then diluted with distilled water to known volumes.

Cu(s) + 4 HNO₃(aq) → Cu(NO₃)₂(aq) + 2 NO₂(g) + 2 H₂O(l)

The students determined that the reaction produced 0.010 mol of Cu(NO₃)₂. Based on the measurement, what was the percent of Cu by mass in the original 2.00 g sample of the mixture?

64%

16%

32%

96%

32%

How many energy levels are represented in the photoelectron spectrum below?

2 energy levels

3 energy levels

1 energy level

5 energy levels

3 energy levels

Which of the following is the electron configuration of an excited atom that is likely to emit a quantum of energy?

1s² 2s²2p⁶ 3s²

1s² 2s²2p⁶ 3s²3p⁵

1s² 2s²2p⁶ 3s¹

1s² 2s²2p⁶ 3s¹3p¹

1s² 2s²2p⁶ 3s²3p¹

1s² 2s²2p⁶ 3s¹3p¹

Which of the following species has the electron configuration shown?

1s² 2s²2p⁶ 3s²3p⁶

O

Cl⁺

K⁺

Ne

K⁺

Of the following electron configurations of neutral atoms, which represents an atom in an excited state?

1s² 2s² 2p⁵

1s² 2s² 2p⁶ 3s¹

1s² 2s² 2p⁶ 3s² 3p⁵

1s² 2s² 2p⁶ 3s² 3p²

1s² 2s² 2p⁵ 3s²

1s² 2s² 2p⁵ 3s²

Cl–

Ar

K+

Ca2+

The four species above have the same electron configuration, 1s² 2s² 2p⁶ 3s² 3p⁶. Which of the following statements correctly identifies the species with the largest radius and provides an explanation based on Coulomb's law?

Ar, because it is a neutral atom and the net force on the electrons in the 3p sublevel is zero.

Ca²⁺, because the large positive charge on the cation causes increased repulsion among the electrons in the 3p sublevel.

K⁺, because the loss of an electron results in a smaller attractive force between the nucleus and the electrons in the 3p sublevel.

Cl^–, because its nuclear charge exerts the least attractive force on the electrons in the 3p sublevel

Cl^–, because its nuclear charge exerts the least attractive force on the electrons in the 3p sublevel

What force allows the electrons to stay within the electron cloud?

The repulsion of the other electrons

The orbital attraction within the subshells

The attractive pull from the positively charged nucleus

The shielding from the core electrons

The attractive pull from the positively charged nucleus

The photoelectron spectra in the figure show the energy required to remove a 1s electron from a nitrogen atom and from an oxygen atom. Which of the following statements best accounts for the peak in the upper spectrum being to the right of the peak in the lower spectrum?

Electrons in the p subshell of oxygen atoms provide more shielding than electrons in the p subshell of nitrogen atoms.

There are more electron-electron repulsions in oxygen atoms than in nitrogen atoms.

Nitrogen atoms have a smaller nuclear charge than oxygen atoms.

Nitrogen atoms have a half-filled p subshell

incorrect

The photoelectron spectra in the figure show the energy required to remove a 1s electron from a nitrogen atom and from an oxygen atom. Which of the following statements best accounts for the peak in the upper spectrum being to the right of the peak in the lower spectrum?

Electrons in the p subshell of oxygen atoms provide more shielding than electrons in the p subshell of nitrogen atoms.

Nitrogen atoms have a half-filled p subshell.

There are more electron-electron repulsions in oxygen atoms than in nitrogen atoms.

Nitrogen atoms have a smaller nuclear charge than oxygen atoms.

incorrect

Which statement is not true?

Br ^-1 is larger than Br because there are more electrons making the Zeff weaker

K⁺¹ is smaller than K because it lost an entire energy level making Zeff stronger

Ca⁺² is smaller than Ca because their are less electrons making the Zeff stronger

O^-2 and O are the same size because they are the same element

O^-2 and O are the same size because they are the same element

Why does oxygen have a slightly lower ionization energy than nitrogen even though the trend has an overall increase across the row?

Oxygen prefers to lose the paired electron in its p-subshell to reduce electron repulsion within the orbital.

Oxygen prefers to lose its s-subshell electrons before its p-subshell electrons to be more stable.

Oxygen is in a higher energy level and experiences more electron shielding than nitrogen making it's Zeff weaker.

Oxygen gains 2 electrons to become an ion which takes less energy than nitrogen gaining 3 electrons to become an ion.

Oxygen prefers to lose the paired electron in its p-subshell to reduce electron repulsion within the orbital

What is electron affinity?

The tendency of an atom to attract an electron to itself

A scale from 0-4 that quantifies determine electron attraction

Describes the stability of the noble gases

The energy (kJ/mol) released when adding an electron to become a negative ion

The energy (kJ/mol) released when adding an electron to become a negative ion

Which of the following correctly identifies which has the highest first-ionization energy, Cl or Ar, and supplies the best justification?

Ar, because of its completely filled valence shell

Ar, because of its higher effective nuclear charge

Cl, because of its higher electronegativity

Cl, because of its higher electron affinity

incorrect

Which of the following best helps explain why the electronegativity of Cl is less than that of F?

Because Cl is larger than F, the repulsions among electrons in the valence shell of Cl are less than the repulsions among electrons in the valence shell of F.

The mass of the Cl atom is greater than the mass of the F atom.

The Cl nucleus contains more protons than the F nucleus contains.

When Cl and F form bonds with other atoms, the Cl bonding electrons are more shielded from the positive Cl nucleus than the F bonding electrons are shielded from the positive F nucleus.

When Cl and F form bonds with other atoms, the Cl bonding electrons are more shielded from the positive Cl nucleus than the F bonding electrons are shielded from the positive F nucleus

Which of the following lists Mg, P, and Cl in order of increasing atomic radius?

Cl < P < Mg

P < Cl < Mg

Mg < P < Cl

Cl < Mg < P

Mg < Cl < P

Cl < P < Mg

For element X represented below, which of the following is the most likely explanation for the large difference between the second and third ionization energies? 

X(g) → X+(g) + e-	IE1 = 740 kJ/mol
X+(g) → X2+(g) + e-	IE2 = 1450 kJ/mol
X2+(g) → X3+(g) + e-	IE3 = 7730 kJ/mol

The effective nuclear charge decreases with successive ionizations.

The ionic radius increases with successive ionizations.

The shielding of outer electrons increases with successive ionizations.

The electron removed during the third ionization is, on average, much closer to the nucleus than the first two electrons removed were.

The electron removed during the third ionization is, on average, much closer to the nucleus than the first two electrons removed were.

Which of the following elements has the largest atomic radius?

Cs

Pb

Ag

Br

Se

Cs

The following table shows the first ionization energy and the atomic radius of several elements. Which of the following best helps to explain the deviation of the first ionization energy of oxygen from the overall trend?

Element	First Ionization Energy (kJ/mol)	Atomic Radius (pm)
B	801	85
C	1086	77
N	1400	75
O	1314	73
F	1680	72
Ne	2080	70

There is attraction between paired electrons in oxygen's 2p orbitals.

The atomic radius of oxygen is less than the atomic radius of nitrogen.

The atomic radius of oxygen is greater than the atomic radius of fluorine.

There is repulsion between paired electrons in oxygen's 2p orbitals.

There is repulsion between paired electrons in oxygen's 2p orbitals

Which of the following elements has the highest electronegativity?

Pb

Cs

Ag

Br

Se

Br

Oxygen forms an ion with a ______ charge and is considered a(n) _________.

2+ ; Anion

2- ; Cation

2+ ; Cation

2- ; Anion

2- ; Anion

Atoms of Mg combine with atoms of F to form a compound. Atoms of which of the following elements combine with atoms of F in the same ratio?

Ba

Li

Al

Cl

Ne

Ba

The compound CCl₄ is nonflammable and was once commonly used in fire extinguishers. On the basis of the periodic properties, which of the following compounds can most likely be used as a fire-resistance chemical?

PbCl₂

CH₄

BCl₃

CBr₄

CBr₄

All the chlorides of the alkaline earth metals have similar empirical formulas, as shown in the table. Which of the following best helps to explain this observation?

Metal	Be	Mg	Ca	Sr	Ba	Ra
Formula of Metal Chloride	BeCl2	MgCl2	CaCl2	SrCl2	BaCl2	RaCl2

Cl has a much greater electronegativity than any of the alkaline earth metals.

The two valence electrons of alkaline earth metal atoms are relatively easy to remove.

The radii of atoms of alkaline earth metals increase moving down the group from Be to Ra.  

Cl₂(g) reacts with metal atoms to form strong, covalent double bonds

The two valence electrons of alkaline earth metal atoms are relatively easy to remove.

When free Cl(g) atoms encounter O₃(g) molecules in the upper atmosphere, the following reaction mechanism is proposed to occur.

Cl(g) + O3(g) → ClO(g) + O2(g)	slow step
ClO(g) + O3(g) → Cl(g) + 2 O2(g)	fast step
2 O3(g) → 3 O2(g)	overall reaction	△H = -285 kJ/molrxn

X + O3 → XO + O2

XO + O3 → X + 2 O2

2 O3 → 3 O2

The proposed mechanism can be written in a more general form, as shown above. Species other than Cl can also decompose O₃ through the same mechanism. Which of the following chemical species is most likely to decompose O₃ in the upper atmosphere through the mechanism in the above mechanism?

N₂

O₂

He

Br

Br

Forms monatomic ions with 2- charge in solutions

S

F

Mg

Ar

Mn

S