Question 1

Which of the following best explains why the Law of Conservation of Mass was a significant advancement in chemistry?
Correct answer: It demonstrated that the total mass remains constant during chemical reactions, supporting the idea that atoms are rearranged but not destroyed.

Accepted Answer

It demonstrated that the total mass remains constant during chemical reactions, supporting the idea that atoms are rearranged but not destroyed.

Question 2

A sample of magnesium is found to contain two isotopes: 24Mg (78.99% abundance, mass = 23.985 amu) and 25Mg (10.00% abundance, mass = 24.986 amu). What is the approximate average atomic mass of magnesium in this sample?
Correct answer: 24.11 amu

Accepted Answer

24.11 amu

Question 3

Which statement 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 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 real-world application relies on the measurement of isotope ratios?
Correct answer: Estimating the year of birth using 14C in tooth enamel

Accepted Answer

Estimating the year of birth using 14C in tooth enamel

Question 6

Which of the following statements about Dalton’s Atomic Theory is no longer considered completely accurate?
Correct answer: Atoms of the same element are identical in mass and properties.

Accepted Answer

Atoms of the same element are identical in mass and properties.

Question 7

A mass spectrometer is used to analyze a sample of chlorine. The spectrum shows two peaks at masses 35 and 37. What does this indicate about chlorine?
Correct answer: Chlorine contains two isotopes with the same number of protons but different numbers of neutrons.

Accepted Answer

Chlorine contains two isotopes with the same number of protons but different numbers of neutrons.

Question 8

Which of the following best describes the location and relative mass of subatomic particles in an atom?
Correct answer: Protons and neutrons are in the nucleus and account for nearly all the mass; electrons are outside the nucleus and have negligible mass.

Accepted Answer

Protons and neutrons are in the nucleus and account for nearly all the mass; electrons are outside the nucleus and have negligible mass.

Question 9

An atom has 17 protons, 18 neutrons, and 17 electrons. What is its mass number and what element is it?
Correct answer: Mass number 35, element chlorine

Accepted Answer

Mass number 35, element chlorine

Question 10

Which of the following scenarios would violate the Law of Definite Proportions?
Correct answer: A compound labeled as water is found to have a hydrogen to oxygen mass ratio of 1:4.

Accepted Answer

A compound labeled as water is found to have a hydrogen to oxygen mass ratio of 1:4.

Question 11

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

Accepted Answer

18

Question 12

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 13

A forensic scientist uses mass spectrometry to analyze a sample and finds a high abundance of 14C. What can this information be used for?
Correct answer: Estimating the age or year of origin of the sample

Accepted Answer

Estimating the age or year of origin of the sample

Question 14

Which of the following is a correct application of Dalton’s postulate that atoms combine in simple whole-number ratios?
Correct answer: Water always forms as H2O, not as H1.5O or H2O1.2.

Accepted Answer

Water always forms as H2O, not as H1.5O or H2O1.2.

Question 15

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 sum of protons and neutrons.

Accepted Answer

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

Question 16

A sample of silicon contains 92.2% 28Si (mass = 27.977 amu), 4.7% 29Si (mass = 28.976 amu), and 3.1% 30Si (mass = 29.974 amu). What is the average atomic mass of silicon?
Correct answer: 28.09 amu

Accepted Answer

28.09 amu

Question 17

Which of the following best explains why most of an atom’s volume is considered empty space?
Correct answer: Electrons are much smaller than protons and neutrons and are spread out far from the nucleus.

Accepted Answer

Electrons are much smaller than protons and neutrons and are spread out far from the nucleus.

Question 18

Which of the following would be the best evidence that two samples are the same compound, according to the Law of Definite Proportions?
Correct answer: They have the same mass ratio of constituent elements.

Accepted Answer

They have the same mass ratio of constituent elements.

Question 19

Which of the following is a correct statement about the charge of an atom?
Correct answer: The charge is determined by the difference between the number of protons and electrons.

Accepted Answer

The charge is determined by the difference between the number of protons and electrons.

Atomic Structure and Isotopes: Foundations and Applications

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