Question 1

Which of the following statements best describes the law of definite proportions as demonstrated by Joseph Proust?
Correct answer: A compound always contains the same elements in the same proportions by mass.

Accepted Answer

A compound always contains the same elements in the same proportions by mass.

Question 2

A forensic scientist is analyzing tooth enamel to estimate a person's year of birth. Which isotope is most likely being measured, and why?
Correct answer: Carbon-14, because its atmospheric abundance changed due to nuclear testing.

Accepted Answer

Carbon-14, because its atmospheric abundance changed due to nuclear testing.

Question 3

Which of the following changes would result in a different element?
Correct answer: Changing the number of protons in the nucleus.

Accepted Answer

Changing the number of protons in the nucleus.

Question 4

A sample of gallium contains two naturally occurring isotopes: 69Ga (mass = 68.93 u, abundance = 60.1%) and 71Ga (mass = 70.92 u, abundance = 39.9%). What is the average atomic mass of gallium? (Round to two decimal places.)
Correct answer: 69.72 u

Accepted Answer

69.72 u

Question 5

Which of the following best explains why the atomic masses listed on the periodic table are not whole numbers?
Correct answer: They are weighted averages of all naturally occurring isotopes of each element.

Accepted Answer

They are weighted averages of all naturally occurring isotopes of each element.

Question 6

Which experiment or observation provided the strongest evidence that most of the mass of an atom is concentrated in a tiny, dense nucleus?
Correct answer: Rutherford's gold foil experiment

Accepted Answer

Rutherford's gold foil experiment

Question 7

A neutral atom of element X has 17 protons and 18 neutrons. Which of the following is correct?
Correct answer: The atom is chlorine-35.

Accepted Answer

The atom is chlorine-35.

Question 8

Which of the following statements about isotopes is correct?
Correct answer: Isotopes of an element have the same number of protons but different numbers of neutrons.

Accepted Answer

Isotopes of an element have the same number of protons but different numbers of neutrons.

Question 9

A mass spectrometer is used to analyze a sample of silicon. The resulting spectrum shows three peaks corresponding to masses 28, 29, and 30. What does this indicate about the sample?
Correct answer: The sample contains three naturally occurring isotopes of silicon.

Accepted Answer

The sample contains three naturally occurring isotopes of silicon.

Question 10

Which of the following best describes Dalton's atomic theory as it relates to chemical reactions?
Correct answer: Atoms are rearranged in chemical reactions but are not created or destroyed.

Accepted Answer

Atoms are rearranged in chemical reactions but are not created or destroyed.

Question 11

A sample contains 80% isotope A (mass = 10 u) and 20% isotope B (mass = 11 u). What is the average atomic mass of the element?
Correct answer: 10.2 u

Accepted Answer

10.2 u

Question 12

Which of the following is a real-world application of isotope analysis in geology?
Correct answer: Determining the age of rocks using uranium-lead dating.

Accepted Answer

Determining the age of rocks using uranium-lead dating.

Question 13

If an atom has 15 protons, 16 neutrons, and 18 electrons, what is its net charge?
Correct answer: 3-

Accepted Answer

3-

Question 14

Which statement about the structure of the atom is supported by modern evidence?
Correct answer: Most of the atom's volume is empty space, with a dense nucleus at the center.

Accepted Answer

Most of the atom's volume is empty space, with a dense nucleus at the center.

Question 15

Which of the following best explains why isotopic abundances are important in determining the average atomic mass of an element?
Correct answer: Because the average atomic mass is a weighted average based on the relative abundance of each isotope.

Accepted Answer

Because the average atomic mass is a weighted average based on the relative abundance of each isotope.

Question 16

Which of the following is NOT a postulate of Dalton's atomic theory?
Correct answer: Atoms can be subdivided into protons, neutrons, and electrons.

Accepted Answer

Atoms can be subdivided into protons, neutrons, and electrons.

Question 17

A scientist is using mass spectrometry to analyze a sample. What information can be directly obtained from the mass spectrum?
Correct answer: The relative abundance and mass of each isotope present in the sample.

Accepted Answer

The relative abundance and mass of each isotope present in the sample.

Question 18

Which of the following best describes the difference between protons and neutrons?
Correct answer: Protons have a positive charge, while neutrons have no charge.

Accepted Answer

Protons have a positive charge, while neutrons have no charge.

Question 19

Which of the following scenarios would violate the law of conservation of mass?
Correct answer: A chemical reaction in which the total mass of products is less than the total mass of reactants.

Accepted Answer

A chemical reaction in which the total mass of products is less than the total mass of reactants.

Atomic Structure and Isotopes: Foundations and Applications

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