Q: Which equation correctly calculates the 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 direct 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 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 statement about isotopes is correct?

Accepted Answer

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

Question 5

Which equation correctly calculates the atomic mass of an element with two isotopes?

Accepted Answer

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

Question 6

A sample of chlorine contains 75.37% $$^{35}Cl ($$atomic mass = 34.969 u) and 24.63% $$^{37}Cl ($$atomic mass = 36.966 u). What is the average atomic mass of chlorine?

Accepted Answer

$$35.45 u$$

Question 7

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

Accepted Answer

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

Question 8

Which of the following best describes the law of conservation of mass?

Accepted Answer

The total mass of reactants equals the total mass of products in a chemical reaction.

Question 9

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

Accepted Answer

Nuclear fission

Question 10

Which instrument is used to separate isotopes based on their mass-to-charge ratio?

Accepted Answer

Mass spectrometer

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 is NOT a postulate of Dalton’s atomic theory?

Accepted Answer

Atoms can be subdivided into protons, neutrons, and electrons.

Question 13

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

Accepted Answer

$$28.09 u$$

Question 14

Which element is defined by having 6 protons in its nucleus?

Accepted Answer

Carbon

Question 15

Which of the following is a correct statement about nucleons?

Accepted Answer

Nucleons are protons and neutrons.

Question 16

Which isotope of gallium is more abundant if the average atomic mass is 69.723 u, $$^{69}Ga $$has a mass of 68.926 u, and $$^{71}Ga $$has a mass of 70.925 u?

Accepted Answer

$$^{69}Ga$$

Question 17

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

Accepted Answer

Atoms are mostly empty space.

Question 18

Which of the following is a real-world use of technetium ($$^{43}Tc$$)?

Accepted Answer

Medical imaging

Question 19

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

Accepted Answer

Law of constant composition (definite proportions)

Question 20

Which of the following best describes the difference between $$^{12}C $$and $$^{14}C$$?

Accepted Answer

$$^{14}C $$has more neutrons than $$^{12}C.$$

Atomic Structure and Isotopes: Foundations of Modern Chemistry

Study Guide - Practice Questions

Study Guide - Flashcards