Question 1

Which of the following best describes why soda pop fizzes when opened, from a molecular perspective?

Accepted Answer

The pressure inside the can forces carbon dioxide molecules to remain dissolved in water; when opened, the pressure drops and carbon dioxide escapes as gas.

Question 2

Which statement correctly distinguishes between a compound and a mixture?

Accepted Answer

A compound has a fixed ratio of elements chemically combined, while a mixture consists of substances physically intermingled in variable proportions.

Question 3

Which of the following is an example of an intensive property?

Accepted Answer

Density

Question 4

A student observes that when ice melts, the mass of water remains the same. Which law does this observation support?

Accepted Answer

Law of Conservation of Mass

Question 5

Which of the following best describes a chemical change?

Accepted Answer

Copper reacting with nitric acid to form a blue solution

Question 6

Which of the following is true about exothermic and endothermic reactions?

Accepted Answer

Exothermic reactions release energy, while endothermic reactions absorb energy.

Question 7

Which of the following is NOT a postulate of Dalton’s Atomic Theory?

Accepted Answer

Atoms of one element can be converted into atoms of another element by chemical reactions.

Question 8

A sample contains only molecules made of two identical atoms bonded together. Which classification best fits this sample?

Accepted Answer

Element

Question 9

Which of the following best describes the difference between a physical and a chemical property?

Accepted Answer

A chemical property describes how a substance interacts with other substances, while a physical property can be observed without changing the substance.

Question 10

Which of the following is a correct representation of the law of multiple proportions?

Accepted Answer

If two elements form more than one compound, the masses of one element that combine with a fixed mass of the other are in ratios of small whole numbers.

Question 11

A sealed can of soda contains carbon dioxide dissolved in water. When the can is opened, bubbles form. Which type of change is this?

Accepted Answer

Physical change

Question 12

Which of the following best describes the scientific method?

Accepted Answer

A systematic approach involving observation, hypothesis, experimentation, and theory development.

Question 13

Which of the following is a correct calculation for the number of neutrons in an isotope of silicon with mass number 29 and atomic number 14?

Accepted Answer

$$29 - 14 = 15$$

Question 14

Which of the following is a real-world example of a homogeneous mixture?

Accepted Answer

A can of soda pop before opening

Question 15

Which of the following best explains why water is a liquid at room temperature while carbon dioxide is a gas?

Accepted Answer

Water molecules are bent, leading to stronger intermolecular forces, while carbon dioxide molecules are linear and have weaker intermolecular forces.

Question 16

Which of the following is NOT a branch of chemistry?

Accepted Answer

Astrology

Question 17

A scientist measures the mass of a sealed flask before and after a chemical reaction and finds no change. Which principle does this support?

Accepted Answer

Law of Conservation of Mass

Question 18

Which of the following best describes an isotope?

Accepted Answer

Atoms of the same element with different numbers of neutrons

Question 19

Which of the following is a correct formula for calculating the atomic mass of an element with two isotopes?

Accepted Answer

$$	ext{Atomic mass} = (	ext{mass of isotope 1}) 	imes (	ext{fractional abundance of isotope 1}) + (	ext{mass of isotope 2}) 	imes (	ext{fractional abundance of isotope 2})$$

Introduction to Chemistry: Matter, Atoms, and Scientific Method

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