Q: Which of the following is the best definition of a mole?

The amount of substance containing $$6.022 \times 10$$^{23}$$ elementary entities

Q: Which of the following is the correct formula to convert grams of a substance to moles?

$$\text{moles} = \frac{\text{grams}}{\text{molar mass}}$$

Question 1

Which of the following best describes the Law of Conservation of Mass as demonstrated by Lavoisier's experiment with mercuric oxide?

Accepted Answer

Matter is neither created nor destroyed during a chemical change; the total mass remains constant.

Question 2

A sample of methane ($$\mathrm{CH_4$}) is $$decomposed to produce carbon and hydrogen in a mass ratio of 3.00:1.00. If you start with 90.0 g of methane, how many grams of hydrogen are produced?

Accepted Answer

$$22.5\ \mathrm{g}$$

Question 3

Which law is illustrated by the fact that silver sulfide ($$\mathrm{Ag_2S}) $$always forms with a 2:1 ratio of silver to sulfur, regardless of the sample?

Accepted Answer

Law of definite proportions

Question 4

Which of the following statements about Dalton’s atomic theory is now known to be incorrect due to the discovery of isotopes?

Accepted Answer

Atoms of a given element are identical in all respects, including mass.

Question 5

Which of the following best explains why carbon can form both carbon monoxide ($$\mathrm{CO}) $$and carbon dioxide ($$\mathrm{CO_2$}) $$when reacting with oxygen?

Accepted Answer

Law of multiple proportions

Question 6

How many moles of $$\mathrm{CO_2$}$$ are present in a 150.0 g sample? (Molar mass of $$\mathrm{CO_2$} is$$ $$44.01\ \mathrm{g/mol})$$

Accepted Answer

$$3.41$$ moles

Question 7

What is the mass, in grams, of $$3.25$$ moles of ammonia ($$\mathrm{NH_3$}$$)? (Molar mass of $$\mathrm{NH_3$} is$$ $$17.03\ \mathrm{g/mol})$$

Accepted Answer

$$55.3\ \mathrm{g}$$

Question 8

Which of the following is the best definition of a mole?

Accepted Answer

The amount of substance containing $$6.022 	imes 10$$^{23}$$ elementary entities

Question 9

Which of the following best describes the difference between an atom and a molecule?

Accepted Answer

A molecule is made of atoms chemically combined in fixed proportions.

Question 10

The term 'atom' comes from the Greek word 'atomos.' What does 'atomos' mean?

Accepted Answer

Cannot be cut

Question 11

Which experiment best illustrates the Law of Definite Proportions?

Accepted Answer

Synthesizing basic copper carbonate from different sources and finding the same elemental composition

Question 12

Which of the following is a real-world example of green chemistry?

Accepted Answer

Replacing rare or hazardous substances with more abundant or less hazardous ones

Question 13

Which of the following statements about the periodic table is correct?

Accepted Answer

Each element is uniquely identified by its atomic number, which is the number of protons.

Question 14

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 15

Which of the following discoveries led to the modification of Dalton’s theory that all atoms of an element are identical?

Accepted Answer

Discovery of isotopes

Question 16

A chemist reacts 10.00 g of lead with 1.55 g of sulfur to form 11.55 g of lead sulfide. If 18.00 g of lead is reacted with 1.55 g of sulfur, how much lead will remain unreacted?

Accepted Answer

$$8.00\ \mathrm{g}$$

Question 17

Which of the following best describes Mendeleev’s contribution to the periodic table?

Accepted Answer

He arranged elements by increasing atomic mass and predicted properties of undiscovered elements.

Question 18

Which of the following is the correct formula to convert grams of a substance to moles?

Accepted Answer

$$	ext{moles} = \frac{	ext{grams}}{	ext{molar mass}}$$

Question 19

Which of the following is a molecule but not an atom?

Accepted Answer

Oxygen ($$\mathrm{O_2$})$$

Question 20

Which of the following best describes why the atomic theory is considered a scientific theory?

Accepted Answer

It is supported by a wide range of experimental evidence and explains observed laws.

Atoms, Atomic Theory, and the Periodic Table: Foundations of Chemistry

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