Question 1

Which statement best describes the law of conservation of mass as discovered by Antoine Lavoisier?

Accepted Answer

The total mass of substances before and after a chemical reaction remains unchanged.

Question 2

Which of the following is a direct consequence of Dalton's atomic theory as originally stated in 1808?

Accepted Answer

Compounds are formed when atoms of different elements combine in small whole-number ratios.

Question 3

Which experiment provided evidence that most of the mass of an atom is concentrated in a tiny, positively charged nucleus?

Accepted Answer

Rutherford's gold foil experiment

Question 4

An atom has 17 protons, 18 neutrons, and 17 electrons. What is its mass number and what element is it?

Accepted Answer

Mass number: 35; Element: Chlorine

Question 5

Which of the following best defines an isotope?

Accepted Answer

Atoms of the same element with different numbers of neutrons

Question 6

A neutral atom of element X has an atomic number of 12 and a mass number of 24. How many protons, neutrons, and electrons does it have?

Accepted Answer

12 protons, 12 neutrons, 12 electrons

Question 7

Which of the following statements about atomic structure is correct?

Accepted Answer

Most of the volume of an atom is empty space occupied by electrons.

Question 8

The charge of an atom is calculated as:

Accepted Answer

Q=p-e, where p is the number of protons and e is the number of electrons.

Question 9

A sample of silicon contains three isotopes: 92.23% Si28 (27.9769 u), 4.67% Si29 (28.9765 u), and 3.10% Si30 (29.9738 u). What is the estimated average atomic mass of silicon?

Accepted Answer

28.09 u

Question 10

Gallium has two naturally occurring isotopes: Ga69 (68.926 u) and Ga71 (70.925 u). The average atomic mass of gallium is 69.723 u. Which isotope is more abundant?

Accepted Answer

Ga69

Question 11

Which of the following is a real-world application of isotopes as described in the study materials?

Accepted Answer

Determining the year of birth by measuring C14 in tooth enamel.

Question 12

Which statement about the atomic number is correct?

Accepted Answer

It is equal to the number of protons in the nucleus and defines the element.

Question 13

Which of the following best explains why the atomic mass of chlorine is not a whole number?

Accepted Answer

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

Question 14

Which of the following statements about mass spectrometry is correct?

Accepted Answer

It separates isotopes based on their mass-to-charge ratio.

Question 15

If an atom has a charge of +1, which of the following must be true?

Accepted Answer

It has one more proton than electron.

Question 16

Which of the following is NOT a postulate of Dalton's original atomic theory?

Accepted Answer

Atoms can be subdivided into smaller particles.

Question 17

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?

Accepted Answer

10.3 u

Atomic Structure and Nuclear Chemistry: Foundations and Applications

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