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

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

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

Forensic dating using $$^{14}\text{C}$$ levels

Question 1

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

Accepted Answer

Mass is neither created nor destroyed during chemical reactions.

Question 2

According to John Dalton's atomic theory, which of the following statements is INCORRECT based on modern understanding?

Accepted Answer

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

Question 3

Which subatomic particle is responsible for defining the atomic number of an element?

Accepted Answer

Proton

Question 4

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

Accepted Answer

Mass number: 35, Atomic number: 17

Question 5

Which of the following best explains why isotopes of the same element have different physical properties?

Accepted Answer

They have different numbers of neutrons.

Question 6

What is the 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 7

A sample of silicon 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

$$28.0855\ 	ext{u}$$

Question 8

Which experimental evidence led to the conclusion that most of an atom is empty space?

Accepted Answer

Rutherford's gold foil experiment

Question 9

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

Accepted Answer

$$-3$$

Question 10

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

Accepted Answer

Forensic dating using $$^{14}	ext{C}$$ levels

Question 11

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

Accepted Answer

Atoms of different elements can have the same mass.

Question 12

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

Accepted Answer

Sodium ($$^{23}	ext{Na})$$

Question 13

What is the charge of an ion with 20 protons and 18 electrons?

Accepted Answer

$$+2$$

Question 14

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

Accepted Answer

Mass spectrometry

Question 15

A gallium sample has two isotopes: $$^{69}	ext{Ga} (68.9256 u) $$and $$^{71}	ext{Ga} (70.925 u). $$The average atomic mass is 69.723 u. Which isotope is more abundant?

Accepted Answer

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

Question 16

Which of the following best describes an isotope?

Accepted Answer

Atoms of the same element with different numbers of neutrons

Question 17

If the atomic number of an atom changes, what else must change?

Accepted Answer

The element itself

Question 18

Which of the following is a general term for a proton or neutron?

Accepted Answer

Nucleon

Question 19

Which statement about the nucleus of an atom is correct?

Accepted Answer

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

Question 20

Which equation correctly expresses the overall charge of an atom?

Accepted Answer

$$	ext{Charge} = \#	ext{protons} - \#	ext{electrons}$$

Atomic Structure and Nuclear Chemistry: Foundations and Applications

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