Q: Which of the following equations correctly calculates the average atomic mass of an element with two isotopes?

$$M_{av} = \frac{(M_1$ \times \%_1) + (M_2$ \times \%_2)}{100}$$

Question 1

Which experiment provided evidence that most of the atom is empty space and led to the discovery of the atomic nucleus?

Accepted Answer

Rutherford's gold foil experiment

Question 2

Which subatomic particle is responsible for the 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 law states that matter cannot be created or destroyed in a chemical reaction?

Accepted Answer

Law of conservation of mass

Question 5

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

Accepted Answer

Number of neutrons

Question 6

Which technique is commonly used to determine the relative abundance of isotopes in a sample?

Accepted Answer

Mass spectrometry

Question 7

Given the following isotopic abundances for silicon: 92.23% $$^{28}\mathrm{Si} (27.9769 u$$), 4.67% $$^{29}\mathrm{Si} (28.9765 u$$), and 3.10% $$^{30}\mathrm{Si} (29.9738 u$$), calculate the average atomic mass of silicon. (Round to two decimal places)

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

A forensic scientist uses $$^{14}\mathrm{C}$$ levels in tooth enamel to estimate a person’s year of birth. This method relies on which property of isotopes?

Accepted Answer

Isotopes have different nuclear properties and decay rates.

Question 10

Which of the following best describes the charge of an atom?

Accepted Answer

Charge = number of protons minus number of electrons

Question 11

If an atom has 17 protons, 18 neutrons, and 18 electrons, what is its net charge?

Accepted Answer

-1

Question 12

Which element is defined by the atomic number $$Z = 6$$?

Accepted Answer

Carbon

Question 13

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

Accepted Answer

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

Question 14

Which of the following is a correct statement about the mass number ($$A) of an $$atom?

Accepted Answer

It is the sum of protons and neutrons.

Question 15

Which real-world application uses isotope ratios for dating biological samples?

Accepted Answer

Carbon-14 dating in archaeology

Question 16

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

Accepted Answer

They are the weighted average of all naturally occurring isotopes.

Question 17

Which of the following equations correctly calculates the average atomic mass of an element with two isotopes?

Accepted Answer

$$M_{av} = \frac{(M_1$ 	imes \%_1) + (M_2$ 	imes \%_2)}{100}$$

Question 18

Which of the following statements about nucleons is correct?

Accepted Answer

Nucleons are protons and neutrons.

Question 19

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 20

Which of the following best describes the role of electrons in the atom?

Accepted Answer

Electrons travel around the nucleus and balance the overall charge of the atom.

Atomic Structure and Nuclear Chemistry: Foundations and Applications

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