AP Chemistry Unit 1 Test

What defines the identity of an atom?

The number of positively charged protons

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

A mole is a quantity and a very helpful counting unit for chemists. How many particles does a mole equal?

1 mole = 6.022 x 10²³ particles

Which of the following numerical expressions gives the number of particles in 2.0 g of Ne?

What is the empirical formula of the compound that is 24.2% Cu, 27.0% Cl, and 48.8% O by mass?

CuCl2O8

Ribose, the sugar found in RNA, contains 40.00% C, 6.71% H, and 53.28% O, with a molar mass of 150.13 g/mol. What is the molecular formula of ribose?

C5H10O5

Which of the following pairs have the same empirical formula?

C6H9 and C10H15

A compound contains 30. percent sulfur and 70. percent fluorine by mass. The empirical formula of the compound is

SF4

Two different ionic compounds each contain only copper and chlorine. Both compounds are powders, one white and one brown. An elemental analysis is performed on each powder. Which of the following questions about the compounds is most likely to be answered by the results of the analysis?

What is the formula unit of each compound?

A student has samples of two pure compounds, XClO₃ and ZClO₃, which contain unknown alkali metals X and Z. The student measures the mass of each sample and then strongly heats the samples to drive off all the oxygen, leaving solid residues of XCl and ZCl. The student measures the mass of the solid residue from each sample. Which of the following questions can be answered from the results of the experiment?

Which has the greater molar mass, X or Z

What number of moles of O₂ is needed to produce 14.2 grams of P₄O₁₀ from P ? (Molecular weight P₄O₁₀ = 284)

0.250 mole

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

CrO2

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 has the higher purity?

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

3.5% NaCl

A sample of a solid labeled as NaCl may be impure. A student analyzes the sample and determines that it contains 75 percent chlorine by mass. Pure NaCl(s) contains 61 percent chlorine by mass. Which of the following statements is consistent with the data?

The sample contains NaCl(s) and LiCl(s).

A student is given two 10g samples, each a mixture of only NaCl(s) and KCl(s) but in different proportions. Which of the following pieces of information could be used to determine which mixture has the higher proportion of KCl(s)?

 

The mass of Cl in each mixture

Consider atoms of the following elements. Assume that the atoms are in the ground state.

The atom that contains only one electron in the highest occupied energy sublevel

Ga

1s² 2s² 2p⁶ 3s² 3p³

 

Atoms of an element, X, have the electronic configuration shown above. The compound most likely formed with magnesium, Mg, is

Mg3X2

Consider atoms of the following elements. Assume that the atoms are in the ground state.

The atom that contains exactly two unpaired electrons

S

The photoelectron spectra of the 1s electrons of two isoelectronic species, Ca²⁺ and Ar, are shown in the figure. Which of the following correctly identifies the species associated with peak X and provides a valid justification?

 

Ca²⁺, because its nucleus has two more protons than the nucleus of Ar has

The complete photoelectron spectra of neutral atoms of two unknown elements, X and Y, are shown in the figure. Which of the following can be inferred from the data?

 

Element Y has a greater nuclear charge than element X does.

Put the following atoms in order from smallest to largest atomic radii:

F < Cl < Br < I

What is meant by the term "effective nuclear charge (Z_eff)"?

The net positive charge experienced by the electron as a result of both nuclear charge and shielding

As protons increase across a row, what happens to Z_eff?

Z_eff gets stronger allowing the nucleus to pull the electrons in closer

Which of the following properties generally decreases across the periodic table from sodium to chlorine?

Atomic radius

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

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 best helps to explain why Na(s) is more reactive with water than Mg(s) is?

The first ionization energy of Na is less than that of Mg.

Which of the following elements has the largest atomic radius?

Cs

Which of the following best helps to account for the fact that the F^-ion is smaller than the O^2- ion?

F^- has a larger nuclear charge than O^2- has.

Based on the ionization energies of element X given in the table, which of the following is most likely the empirical formula of an oxide of element X?

 

	Ionization Energy (kJ/mol)
First	577
Second	1,816
Third	2,745
Fourth	11,577
Fifth	14,482

X2O3

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

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

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

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

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

Which of the following ions has the same number of electrons as Br^- ?

Sr2+

Forms monatomic ions with 2- charge in solutions

S