AP Chemistry Unit 1 AP Exam Prep Quizzes

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?

Molar mass of the compound, mass of the sample

A solution is prepared by adding 16 g of CH₃OH (molar mass 32 g) to 90 g of H₂O (molar mass 18 g). The mole fraction of CH₃OH in this solution is closest to which of the following?

0.1

According to the information in the table, a 1.00 g sample of which of the following contains the greatest mass of oxygen?

Table: Compounds and Molar Masses

Compound	Molar Mass (grams)
Na2O	62.0
MgO	40.3
K2O	94.2
CaO	56.1

MgO

The mass spectrum of an average sample of a pure element is shown in the figure. Which of the following is the identity of the element?

 

Zr

The mass spectrum of element X is presented in the diagram. Based on the spectrum, which of the following can be concluded about element X?

 

The atomic mass of X is between 90 and 92.

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?

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?

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

0.250 mole

The percentage of silver in a solid sample is determined gravimetrically by converting the silver to Ag⁺(aq) and precipitating it as silver chloride. Failure to do which of the following could cause errors in the analysis?

 

I. Account for the mass of the weighing paper when determining the mass of the sample

II. Measure the temperature during the precipitation reaction

III. Wash the precipitate

IV. Heat the AgCl precipitate to constant mass

I, III, and IV

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).

Which of the following best represents the ground-state electron configuration for an atom of selenium?

1s² 2s²2p⁶ 3s²3p⁶ 4s² 3d¹⁰ 4p⁴

Which of the following represents a pair of isotopes?

Atomic Number | Mass Number

I. 7 | 13

II. 7 | 14

How many protons, neutrons, and electrons are in an  atom?

Protons	Neutrons	Electrons
26	30	26

Which of the following species has the electron configuration shown?

1s² 2s²2p⁶ 3s²3p⁶

K⁺

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

1s² 2s²2p⁶ 3s¹3p¹

Which of the following best helps to explain why the electron affinity of Br has a greater magnitude than that of I?

There is a greater attraction between an added electron and the nucleus in Br than in I.

Which of the following correctly compares periodic properties of two elements and provides an accurate explanation for that difference?

The atomic radius of Cl is smaller than that of S because Cl has a larger nuclear charge than S does.

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

Atomic radius

Forms monatomic ions with 2- charge in solutions

S

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?

Br