Q: Which of the following is the correct formula for calculating the average atomic mass of an element with multiple isotopes?

$$\text{Average atomic mass} = \sum (\text{isotope mass} \times \text{fractional abundance})$$

Question 1

Which of the following statements best describes the law of conservation of mass as established by Antoine Lavoisier?

Accepted Answer

The total mass of substances present after a chemical reaction is the same as the total mass before the reaction.

Question 2

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 3

An atom of carbon-14 ($$^{14}\mathrm{C}) $$has how many protons, neutrons, and electrons (in a neutral atom)?

Accepted Answer

6 protons, 8 neutrons, 6 electrons

Question 4

Which of the following is the correct formula for calculating the average atomic mass of an element with multiple isotopes?

Accepted Answer

$$	ext{Average atomic mass} = \sum (	ext{isotope mass} 	imes 	ext{fractional abundance})$$

Question 5

A sample of silicon 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 estimated average atomic mass of silicon?

Accepted Answer

Approximately 28.09 u

Question 6

Which statement about isotopes is correct?

Accepted Answer

Isotopes of an element have the same number of protons but different numbers of neutrons.

Question 7

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

Accepted Answer

Chlorine exists as a mixture of isotopes, and the atomic mass is a weighted average of their masses.

Question 8

A neutral atom has 17 protons and 18 neutrons. What is its atomic number and mass number?

Accepted Answer

Atomic number = 17, mass number = 35

Question 9

Which of the following real-world applications relies on the measurement of isotope ratios?

Accepted Answer

Determining the year of birth from tooth enamel using $$^{14}\mathrm{C}$$ levels

Question 10

Which of the following statements about Dalton's atomic theory is now known to be incorrect?

Accepted Answer

All atoms of a given element are identical in mass and in all other properties.

Question 11

If an atom has a charge of $$+2$$, 20 protons, and 18 electrons, what is its atomic number?

Accepted Answer

20

Question 12

Which of the following best describes a nucleon?

Accepted Answer

A nucleon is a general term for a proton or neutron.

Question 13

Gallium has two naturally occurring isotopes: $$^{69}\mathrm{Ga} (68.926 u) $$and $$^{71}\mathrm{Ga} (70.925 u). $$The average atomic mass of gallium is 69.723 u. Which isotope is more abundant?

Accepted Answer

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

Question 14

Which of the following is the correct expression for the charge of an atom?

Accepted Answer

$$	ext{Charge} = 	ext{number of protons} - 	ext{number of electrons}$$

Question 15

Which of the following best explains why most of the volume of an atom is empty space?

Accepted Answer

Electrons occupy regions far from the tiny, dense nucleus.

Question 16

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

Accepted Answer

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

Atomic Structure and Nuclear Chemistry: Foundations and Applications

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