Question 1

Which experiment provided direct evidence for the existence of atoms and molecules by observing the random motion of particles suspended in a fluid?

Accepted Answer

Brownian motion observed by Robert Brown

Question 2

According to the law of conservation of mass, what will be the total mass of products if 10 g of hydrogen reacts completely with 80 g of oxygen to form water?

Accepted Answer

$$90\ \mathrm{g}$$

Question 3

Which of the following best describes the law of definite proportions?

Accepted Answer

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

Question 4

A sample of carbon monoxide (CO) contains $$9\ \mathrm{g} of $$carbon. According to the law of definite proportions, how many grams of oxygen does it contain? (The mass ratio of C:O in CO is 3:4.)

Accepted Answer

$$12\ \mathrm{g}$$

Question 5

Which statement best captures one of the differences between the law of definite proportions and the law of multiple proportions?

Accepted Answer

The law of definite proportions applies to different samples of a single compound, while the law of multiple proportions compares different compounds with the same elements.

Question 6

Which philosopher first proposed that matter is composed of small, indestructible particles called atoms?

Accepted Answer

Democritus

Question 7

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

Accepted Answer

Atoms of one element can change into atoms of another element during a chemical reaction.

Question 8

A chemist analyzes three samples of ammonia and finds the mass ratio of nitrogen to hydrogen is always $$14:3. $$Which law does this observation support?

Accepted Answer

Law of definite proportions

Question 9

If $$10\ \mathrm{g} of $$element A combines with $$20\ \mathrm{g} of $$element B to form compound AB, and $$10\ \mathrm{g} of $$element A combines with $$40\ \mathrm{g} of $$element B to form compound AB$$_2$$, what is the ratio of the masses of B that combine with a fixed mass of A?

Accepted Answer

$$1:2$$

Question 10

Which of the following real-world scenarios best illustrates the law of conservation of mass?

Accepted Answer

A sealed container of water is heated and the mass remains the same after it turns to steam.

Question 11

Which of the following statements is consistent with Dalton’s atomic theory as it relates to chemical reactions?

Accepted Answer

Atoms are rearranged in chemical reactions, but the atoms themselves are unchanged.

Question 12

A student claims that a $$36\ \mathrm{g}$$ sample of water contains $$8\ \mathrm{g} of $$hydrogen and $$28\ \mathrm{g} of $$oxygen. Which law does this claim violate?

Accepted Answer

Law of definite proportions

Question 13

Which of the following best explains why the mass of rusted iron is greater than the mass of the original iron?

Accepted Answer

Oxygen from the air combines with iron, increasing the total mass.

Question 14

Which of the following is a real-world example of the law of multiple proportions?

Accepted Answer

Carbon forms both carbon monoxide (CO) and carbon dioxide (CO$$_2) $$with oxygen, and the ratio of oxygen masses that combine with a fixed mass of carbon is a small whole number.

Question 15

If $$18\ \mathrm{g} of $$water contains $$2\ \mathrm{g} of $$hydrogen and $$16\ \mathrm{g} of $$oxygen, what is the mass ratio of hydrogen to oxygen in water?

Accepted Answer

$$1:8$$

Question 16

Which of the following statements about atoms is supported by modern atomic theory?

Accepted Answer

Atoms of a given element have the same mass and properties.

Question 17

A scientist finds that $$10\ \mathrm{g} of $$element X reacts with $$20\ \mathrm{g} of $$element Y to form compound XY, and $$10\ \mathrm{g} of X $$reacts with $$40\ \mathrm{g} of Y to $$form compound XY$$_2. $$Which law does this observation support?

Accepted Answer

Law of multiple proportions

Question 18

Which of the following best describes the difference between the atomic theories of Democritus and Aristotle?

Accepted Answer

Democritus believed matter was made of indivisible atoms, while Aristotle believed matter was continuous and composed of four elements.

Question 19

Which of the following is a direct application of the law of conservation of mass in a medical context?

Accepted Answer

The total mass of reactants and products in a metabolic reaction in the human body remains constant.

Atoms and Elements: Foundations of Modern Atomic Theory

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