Question 1

Which of the following best describes the law of constant composition?

Accepted Answer

A compound always contains the same elements in the same proportion by mass.

Question 2

A sample of water from a river and a sample of water from a laboratory are analyzed. Both are found to contain 11.1% hydrogen and 88.9% oxygen by mass. Which law does this observation support?

Accepted Answer

Law of Constant Composition

Question 3

Which experiment provided the first direct evidence for the existence of subatomic particles?

Accepted Answer

Thomson’s cathode ray tube experiment

Question 4

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

Accepted Answer

Atoms are composed of protons, neutrons, and electrons.

Question 5

A 10.0 g sample of compound X contains 4.0 g of element A and 6.0 g of element B. Another sample of compound X with a mass of 20.0 g will contain:

Accepted Answer

8.0 g of A and 12.0 g of B

Question 6

Which law is illustrated by the fact that carbon and oxygen can form both CO and CO$_2$, with the ratio of the mass of oxygen that combines with a fixed mass of carbon being a small whole number?

Accepted Answer

Law of Multiple Proportions

Question 7

Which scientist is credited with discovering the electron and measuring its charge-to-mass ratio?

Accepted Answer

J.J. Thomson

Question 8

The atomic number of an element is defined as:

Accepted Answer

The number of protons in the nucleus

Question 9

Which of the following statements about isotopes is correct?

Accepted Answer

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

Question 10

Which of the following best explains why the mass of an atom is concentrated in its nucleus?

Accepted Answer

The nucleus contains both protons and neutrons, which are much more massive than electrons.

Question 11

A neutral atom of potassium (K) has an atomic number of 19 and an atomic mass of 39. How many neutrons does it have?

Accepted Answer

20

Question 12

Which of the following is a correct empirical formula for a compound with a molecular formula of C$_6$H$_{12}$O$_6$?

Accepted Answer

CH$_2$O

Question 13

Which of the following elements is a diatomic molecule in its natural state?

Accepted Answer

Nitrogen

Question 14

Which of the following ions is a polyatomic cation?

Accepted Answer

NH$_4^+$

Question 15

What is the correct name for the compound Fe$_2$O$_3$?

Accepted Answer

Iron(III) oxide

Question 16

Which of the following is the correct formula for magnesium phosphate?

Accepted Answer

Mg$_3$(PO$_4$)$_2$

Question 17

Which of the following is the correct name for H$_2$SO$_4$?

Accepted Answer

Sulfuric acid

Question 18

Which of the following statements about metals is true?

Accepted Answer

Metals are shiny and good conductors of heat.

Question 19

Which of the following is the correct name for the compound N$_2$O$_5$?

Accepted Answer

Dinitrogen pentoxide

Question 20

A sample of chlorine gas is analyzed and found to contain two isotopes: $^{35}$Cl (75.8%) and $^{37}$Cl (24.2%). What is the average atomic mass of chlorine? (Use: $^{35}$Cl = 34.969 amu, $^{37}$Cl = 36.966 amu)

Accepted Answer

$35.45$ amu

Atoms, Molecules, and Atomic Theory: Foundations of Chemistry

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