Question 1

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

Accepted Answer

A chemical compound always contains exactly the same proportion of elements by mass.

Question 2

A sample of pure water from a river in Asia and a sample from a glacier in Antarctica are analyzed and found to contain hydrogen and oxygen in a mass ratio of approximately 1:8. This observation supports which chemical law?
Correct answer: Law of Definite Proportions

Accepted Answer

Law of Definite Proportions

Question 3

Which of the following changes would result in the formation of 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 neutral atom of element X 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 the atomic mass of chlorine listed on the periodic table is not a whole number?
Correct answer: It is a weighted average of the masses of all naturally occurring isotopes of chlorine.

Accepted Answer

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

Question 6

Which subatomic particle is responsible for the chemical identity of an element?
Correct answer: Proton

Accepted Answer

Proton

Question 7

A scientist uses mass spectrometry to analyze a sample of magnesium and finds three peaks corresponding to masses of 24, 25, and 26. What does this indicate about magnesium?
Correct answer: Magnesium exists as a mixture of isotopes with different numbers of neutrons.

Accepted Answer

Magnesium exists as a mixture of isotopes with different numbers of neutrons.

Question 8

Which of the following real-world applications relies on the properties of isotopes?
Correct answer: Using carbon-14 to estimate the age of archaeological artifacts

Accepted Answer

Using carbon-14 to estimate the age of archaeological artifacts

Question 9

An atom has 17 protons, 18 neutrons, and 18 electrons. What is the charge and identity of this atom?
Correct answer: It is a chloride ion (Cl−) with a −1 charge.

Accepted Answer

It is a chloride ion (Cl−) with a −1 charge.

Question 10

Which statement about Dalton’s Atomic Theory is no longer considered completely accurate based on modern scientific understanding?
Correct answer: Atoms are indivisible and cannot be broken down into smaller particles.

Accepted Answer

Atoms are indivisible and cannot be broken down into smaller particles.

Question 11

A sample contains 70% isotope A (mass = 10 u) and 30% isotope B (mass = 11 u). What is the average atomic mass of the element?
Correct answer: 10.3 u

Accepted Answer

10.3 u

Question 12

Which of the following best describes the distribution of mass and volume in an atom?
Correct answer: Most of the mass is concentrated in the nucleus, while most of the volume is empty space occupied by electrons.

Accepted Answer

Most of the mass is concentrated in the nucleus, while most of the volume is empty space occupied by electrons.

Question 13

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 14

Which of the following is true about isotopes of a given element?
Correct answer: They have the same number of protons but different numbers of neutrons.

Accepted Answer

They have the same number of protons but different numbers of neutrons.

Question 15

A neutral atom of sodium (Na) has an atomic number of 11. If it loses one electron, what is the resulting charge and what is it called?
Correct answer: It becomes a cation with a +1 charge, called Na⁺.

Accepted Answer

It becomes a cation with a +1 charge, called Na⁺.

Question 16

Which of the following best explains why isotopic analysis is useful in forensic science?
Correct answer: Isotopic ratios can be used to trace the origin or age of biological samples.

Accepted Answer

Isotopic ratios can be used to trace the origin or age of biological samples.

Question 17

Which of the following is a direct consequence of Dalton’s postulate that atoms of different elements have different masses?
Correct answer: Compounds have unique, fixed mass ratios of their constituent elements.

Accepted Answer

Compounds have unique, fixed mass ratios of their constituent elements.

Question 18

A sample of silicon contains 92.2% 28Si (mass = 27.98 u), 4.7% 29Si (mass = 28.98 u), and 3.1% 30Si (mass = 29.97 u). What is the average atomic mass of silicon? (Round to two decimal places.)
Correct answer: 28.09 u

Accepted Answer

28.09 u

Atomic Structure and Isotopes: Foundations and Applications

Study Guide - Practice Questions

Study Guide - Flashcards