Question 1

Which of the following statements best describes the Law of Definite Proportions as established by Proust?
Correct answer: A compound always contains the same elements in the same proportion by mass.

Accepted Answer

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

Question 2

A sample of magnesium contains three naturally occurring isotopes: 24Mg (78.99%, mass = 23.985 amu), 25Mg (10.00%, mass = 24.986 amu), and 26Mg (11.01%, mass = 25.983 amu). What is the average atomic mass of magnesium? (Round to two decimal places.)
Correct answer: 24.31 amu

Accepted Answer

24.31 amu

Question 3

Which experiment or observation most directly led to the conclusion that most of an atom's mass is concentrated in a small, dense nucleus?
Correct answer: Rutherford's gold foil experiment

Accepted Answer

Rutherford's gold foil experiment

Question 4

A neutral atom of phosphorus has an atomic number of 15 and a mass number of 31. How many neutrons does it contain?
Correct answer: 16

Accepted Answer

16

Question 5

Which of the following best explains why isotopes of the same element have nearly identical chemical properties?
Correct answer: They have the same number of electrons and protons.

Accepted Answer

They have the same number of electrons and protons.

Question 6

A scientist uses mass spectrometry to analyze a sample of chlorine and finds two peaks corresponding to masses of 35 amu and 37 amu. What does this indicate about chlorine?
Correct answer: Chlorine exists as a mixture of isotopes with different masses.

Accepted Answer

Chlorine exists as a mixture of isotopes with different masses.

Question 7

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

Accepted Answer

Changing the number of protons in the atom

Question 8

A carbon atom has 6 protons, 8 neutrons, and 6 electrons. What is its mass number and what is the name of this isotope?
Correct answer: Mass number = 14; isotope = carbon-14

Accepted Answer

Mass number = 14; isotope = carbon-14

Question 9

Which of the following real-world applications relies on the use of isotopes?
Correct answer: Estimating the age of archaeological artifacts using carbon-14

Accepted Answer

Estimating the age of archaeological artifacts using carbon-14

Question 10

A neutral atom of an element has 17 protons and 18 neutrons. What is the correct symbol for this isotope?
Correct answer: 35Cl

Accepted Answer

35Cl

Question 11

Which statement about Dalton’s atomic theory is now known to be incorrect based on modern understanding?
Correct answer: Atoms are indivisible and indestructible.

Accepted Answer

Atoms are indivisible and indestructible.

Question 12

If an atom has a net charge of -2, 16 protons, and 18 neutrons, how many electrons does it have?
Correct answer: 18

Accepted Answer

18

Question 13

Which of the following best describes the difference between atomic number and mass number?
Correct answer: Atomic number is the number of protons; mass number is the total number of protons and neutrons.

Accepted Answer

Atomic number is the number of protons; mass number is the total number of protons and neutrons.

Question 14

A sample of silicon contains 92.23% 28Si (mass = 27.977 amu), 4.67% 29Si (mass = 28.976 amu), and 3.10% 30Si (mass = 29.974 amu). What is the average atomic mass of silicon? (Round to two decimal places.)
Correct answer: 28.09 amu

Accepted Answer

28.09 amu

Question 15

Which of the following best explains why the atomic mass of an element on the periodic table is rarely a whole number?
Correct answer: It is a weighted average of the masses of all naturally occurring isotopes.

Accepted Answer

It is a weighted average of the masses of all naturally occurring isotopes.

Question 16

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.

Question 17

Which statement about subatomic particles is correct?
Correct answer: Protons and neutrons are located in the nucleus, while electrons are found outside the nucleus.

Accepted Answer

Protons and neutrons are located in the nucleus, while electrons are found outside the nucleus.

Question 18

Which of the following best describes the use of mass spectrometry in chemistry?
Correct answer: It identifies and quantifies isotopes based on their mass and abundance.

Accepted Answer

It identifies and quantifies isotopes based on their mass and abundance.

Question 19

A hospital uses a radioactive isotope to trace blood flow in a patient. Which property of isotopes makes this possible?
Correct answer: Isotopes of the same element have different masses and some are radioactive.

Accepted Answer

Isotopes of the same element have different masses and some are radioactive.

Foundations of Atomic Structure and Isotopes

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