ap chem unit 1 progress check

Based on the mass spectrum of a pure element represented above, the average atomic mass of the element is closest to which of the following?

186.3 amu

Rb reacts with O in a mole ratio of 2 to 1, forming the ionic compound Rb2O. Which of the following elements will react with O in a mole ratio of 2 to 1, forming an ionic compound, and why?

Cs, because it is in the same group as Rb.

Ba2+(aq) + SO42−(aq) → BaSO4(s) A student obtains a 10.0g sample of a white powder labeled as BaCl2. After completely dissolving the powder in 50.0mL of distilled water, the student adds excess Na2SO4(s), which causes a precipitate of BaSO4(s) to form, as represented by the equation above. The student filters the BaSO4(s), rinses it, and dries it until its mass is constant. Which of the following scientific questions could best be answered based on the results of the experiment?

Is the BaCl2(s) used in the experiment pure?

A vessel contains a mixture of gases. The mass of each gas used to make the mixture is known. Which of the following information is needed to determine the mole fraction of each gas in the mixture?

The molar mass of each gas

A 42.0g sample of compound containing only C and H was analyzed. The results showed that the sample contained 36.0g of C and 6.0g of H. Which of the following questions about the compound can be answered using the results of the analysis?

What is the empirical formula of the compound?

What charge does Al typically have in ionic compounds, and why?

+3, because it has three valence electrons.

1s2 2s2 2p6 3s2 3p6 How many unpaired electrons are in the atom represented by the electron configuration above?

0

Which of the following is the correct electron configuration for a ground-state atom of magnesium (atomic number 12) ?

1s2 2s2 2p6 3s2

Which of the following numerical expressions gives the number of moles in 5.0g of CaO?

5.0g / 56g/mol

The mass spectrum for an unknown element is shown above. According to the information in the spectrum, the atomic mass of the unknown element is closest to

91 amu

A 1.0 mol sample of which of the following compounds has the greatest mass?

N2O5

The mass spectrum represented above is most consistent with which of the following elements?

Gd

Which of the following best helps explain why an atom of Rb gas more easily loses an electron in a chemical reaction than an atom of Li gas?

In the Rb atom the valence electron is farther from its nucleus than the valence electron of Li is from its nucleus.

A jar labeled NaCl contains a powder. The table above contains information determined by analyzing a sample of the powder in the laboratory. What information in the table is the most helpful in determining whether the powder is pure NaCl?

Mass percent of Na

The complete photoelectron spectrum of an element is given above. Which labeled peak corresponds to the 1s electrons and why?

Peak X, because 1s electrons have the strongest attractions to the nucleus.

The atomic radii of the elements in the nitrogen group in the periodic table are given in the table above. Which of the following best helps explain the trend of increasing atomic radius from N to Bi?

The attractive force between the valence electrons and the nuclei of the atoms decreases.

The photoelectron spectrum for the element boron is represented above. Which of the following best explains how the spectrum is consistent with the electron shell model of the atom?

The spectrum shows a single electron in the 2p subshell.

Which of the following best helps to explain why the atomic radius of K is greater than that of Br?

The effective nuclear charge experienced by valence electrons is smaller for K than for Br.

In a lab, a student is given a 21g sample of pure Cu metal. Which of the following pieces of information is most useful for determining the number of Cu atoms in the sample? Assume that the pressure and temperature in the lab are 1.0 atm and 25 degrees C.

The molar mass of Cu

The complete photoelectron spectrum of the element carbon is represented above. Which of the following best explains how the spectrum is consistent with the electron shell model of the atom?

The spectrum shows equal numbers of electrons in the three occupied electron subshells.

Which of the following best helps explain why the first ionization energy of K is less than that of Ca?

The valence electron of K experiences a lower effective nuclear charge than the valence electrons of Ca.

A student measures the mass of a sample of a metallic element, M. Then the student heats the sample in air, where it completely reacts to form the compound MO. The student measures the mass of the compound that was formed. Which of the following questions can be answered from the results of the experiment?

What is the molar mass of M?

A student obtains a mixture of the chlorides of two unknown metals, X and Z. The percent by mass of X and the percent by mass of Z in the mixture is known. Which of the following additional information is most helpful in calculating the mole percent of XCl(s) and of ZCl(s) in the mixture?

molar masses of X and Z