Q: Which formula is used to calculate the weighted average atomic mass of an element?

$$M_{av} = \sum \left( \frac{\text{abundance } \%}{100} \times M_{\text{isotope}} \right)$$

Question 1

Which experiment provided direct evidence for the existence of a small, dense, positively charged nucleus at the center of the atom?

Accepted Answer

Rutherford's gold foil experiment

Question 2

Which subatomic particle is responsible for the chemical identity of an element?

Accepted Answer

Proton

Question 3

A neutral atom of gold has 79 protons and 118 neutrons. How many electrons does it have?

Accepted Answer

79

Question 4

Which of the following best describes isotopes?

Accepted Answer

Atoms of the same element with different numbers of neutrons

Question 5

The atomic mass of chlorine is 35.4527 u. Which technique is commonly used to determine the isotopic composition of chlorine in a sample?

Accepted Answer

Mass spectrometry

Question 6

Which law states that the total mass of reactants equals the total mass of products in a chemical reaction?

Accepted Answer

Law of conservation of mass

Question 7

A sample contains 92.23% $$^{28}\mathrm{Si} (27.9769 u$$), 4.67% $$^{29}\mathrm{Si} (28.9765 u$$), and 3.10% $$^{30}\mathrm{Si} (29.9738 u). $$What is the average atomic mass of silicon?

Accepted Answer

$$28.09\ \mathrm{u}$$

Question 8

Which statement about Dalton’s atomic theory is now known to be incorrect?

Accepted Answer

Atoms are indestructible and retain their identity in all chemical reactions.

Question 9

Which real-world application uses isotope ratios to determine the year of birth from tooth enamel?

Accepted Answer

Forensic analysis using $$^{14}\mathrm{C}$$ levels

Question 10

If an atom has 15 protons, 16 neutrons, and 18 electrons, what is its charge?

Accepted Answer

$$-3$$

Question 11

Which element is defined by the atomic number $$Z = 43$$ and is used in medical imaging?

Accepted Answer

Technetium

Question 12

Which of the following is a direct consequence of the law of definite proportions?

Accepted Answer

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

Question 13

A mass spectrometer separates ions based on which property?

Accepted Answer

Their mass-to-charge ratio

Question 14

Which process is illustrated by the splitting of $$^{235}\mathrm{U}$$ into $$^{92}\mathrm{Kr}$$ and $$^{141}\mathrm{Ba}$$, releasing energy?

Accepted Answer

Nuclear fission

Question 15

If the average atomic mass of gallium is 69.723 u, and the masses of its isotopes are 68.926 u ($$^{69}\mathrm{Ga}) $$and 70.925 u ($$^{71}\mathrm{Ga}$$), which isotope is more abundant?

Accepted Answer

$$^{69}\mathrm{Ga}$$

Question 16

Which of the following best explains why most alpha particles pass straight through the gold foil in Rutherford’s experiment?

Accepted Answer

Atoms are mostly empty space

Question 17

Which formula is used to calculate the weighted average atomic mass of an element?

Accepted Answer

$$M_{av} = \sum \left( \frac{	ext{abundance } \%}{100} 	imes M_{	ext{isotope}} ight)$$

Question 18

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

Accepted Answer

Atoms can be subdivided into protons, neutrons, and electrons

Question 19

Which real-world technology relies on the properties of silicon atoms and their isotopes?

Accepted Answer

Solar panels

Question 20

Which of the following statements about subatomic particles is correct?

Accepted Answer

Electrons have a negative charge and are found in the outer region of the atom

Atomic Structure and Nuclear Chemistry: Foundations and Applications

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