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

$$\sum \text{(mass of isotope)} \times \text{(fractional abundance)}$$

Question 1

Which scientist is credited with the discovery of the law of conservation of mass?

Accepted Answer

Antoine Lavoisier

Question 2

According to Dalton’s atomic theory, which statement is INCORRECT based on modern understanding?

Accepted Answer

Atoms of a given element are identical in mass and properties.

Question 3

What is the charge of an atom with 17 protons and 18 electrons?

Accepted Answer

$$-1$$

Question 4

Which experiment provided evidence that most of an atom is empty space?

Accepted Answer

Rutherford’s gold foil experiment

Question 5

What is the main difference between isotopes of the same element?

Accepted Answer

Number of neutrons

Question 6

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

Accepted Answer

$$\sum 	ext{(mass of isotope)} 	imes 	ext{(fractional abundance)}$$

Question 7

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

Accepted Answer

$$28.09\ 	ext{u}$$

Question 8

If the atomic number ($$Z) of an $$atom is 15 and its mass number ($$A) is 31$$, how many neutrons does it have?

Accepted Answer

$$16$$

Question 9

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

Accepted Answer

Forensic science

Question 10

Which subatomic particle has a mass of approximately $$1.674927 	imes 10$$^{-27}$$\ 	ext{kg}$$ and no charge?

Accepted Answer

Neutron

Question 11

A chlorine atom has an average atomic mass of $$35.4527\ 	ext{u}. If$$ $$^{35}	ext{Cl}$$ and $$^{37}	ext{Cl}$$ are the only isotopes, which isotope is more abundant?

Accepted Answer

$$^{35}	ext{Cl}$$

Question 12

Which statement best describes the nucleus of an atom?

Accepted Answer

It contains most of the atom’s mass and is positively charged.

Question 13

Which law states that a chemical compound always contains the same proportion of elements by mass?

Accepted Answer

Law of constant composition

Question 14

What is the charge of a gallium ion with 31 protons and 28 electrons?

Accepted Answer

$$+3$$

Question 15

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 16

Which technique is commonly used to measure the proportions of isotopes in a sample?

Accepted Answer

Mass spectrometry

Question 17

If an atom has 20 protons, 22 neutrons, and 18 electrons, what is its atomic number and net charge?

Accepted Answer

Atomic number: $$20$$, Net charge: $$+2$$

Question 18

Which of the following elements has only one naturally occurring isotope?

Accepted Answer

$$^{19}	ext{F}$$

Question 19

A sample of gallium contains $$^{69}	ext{Ga} (68.9256 u) $$and $$^{71}	ext{Ga} (70.925 u) $$with an average atomic mass of 69.723 u. Which isotope is more abundant?

Accepted Answer

$$^{69}	ext{Ga}$$

Question 20

Which of the following best explains why atomic masses on the periodic table are not whole numbers?

Accepted Answer

They are weighted averages of all naturally occurring isotopes.

Atomic Structure and Nuclear Chemistry: Foundations and Applications

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