Question 1

Which of the following best describes a molecule?

Accepted Answer

A molecule is a group of atoms bonded in a specific shape and composition.

Question 2

Which of the following is the correct chemical formula for water, and what does it indicate about the composition of water molecules?

Accepted Answer

The chemical formula for water is $$\mathrm{H_2O}$$, indicating each molecule contains two hydrogen atoms and one oxygen atom.

Question 3

Which of the following statements about mixtures and pure substances is correct?

Accepted Answer

A mixture contains two or more substances that retain their individual properties.

Question 4

A student observes that the ratio of hydrogen to oxygen in water is always $$2:1 by $$number of atoms, regardless of the sample size. Which law does this observation support?

Accepted Answer

Law of Definite Proportions

Question 5

Which of the following is an example of a homogeneous mixture?

Accepted Answer

Salt dissolved in water

Question 6

Which step in the scientific method involves proposing a tentative explanation for an observation?

Accepted Answer

Formulating a hypothesis

Question 7

A scientist measures the mass of a compound and finds it to be $$200.0\ \mathrm{g}$$, containing $$100.0\ \mathrm{g} of $$element X and $$100.0\ \mathrm{g} of $$element Y. What is the mass percent of element X in the compound?

Accepted Answer

$$50\%$$

Question 8

Which of the following best describes a chemical change?

Accepted Answer

A process in which the composition of a substance is altered, producing new substances.

Question 9

Which of the following is NOT a characteristic of a scientific theory?

Accepted Answer

It is a guess with no supporting evidence.

Question 10

A graph shows the concentration of atmospheric carbon dioxide increasing from $$315\ \mathrm{ppm} in 1958 to$$ $$370\ \mathrm{ppm} in 2000. $$What is the average rate of increase per year over this period?

Accepted Answer

$$1.06\ \mathrm{ppm/year}$$

Question 11

Which of the following best explains why the properties of a compound are different from those of the elements that compose it?

Accepted Answer

The atoms in a compound lose their individual identities and form new substances with unique properties.

Question 12

Which of the following is an example of a heterogeneous mixture?

Accepted Answer

Concrete

Question 13

A sample of a compound contains $$32.0\ \mathrm{g} of $$sulfur and $$32.0\ \mathrm{g} of $$oxygen. What is the ratio of the mass of sulfur to oxygen in the compound?

Accepted Answer

$$1:1$$

Question 14

Which of the following best describes the difference between a law and a theory in science?

Accepted Answer

A law summarizes observations, while a theory provides an explanation for them.

Question 15

Which of the following is a correct statement about atoms and molecules?

Accepted Answer

Molecules are composed of atoms bonded together.

Question 16

A mixture of sand and salt is an example of which type of matter, and how can it be separated?

Accepted Answer

It is a heterogeneous mixture and can be separated by dissolving the salt in water and filtering.

Question 17

Which of the following best describes the process of developing a scientific law?

Accepted Answer

A scientific law is developed by summarizing a large number of consistent experimental observations.

Question 18

If a compound is always composed of the same elements in the same ratio by mass, which law does this illustrate?

Accepted Answer

Law of Definite Proportions

Question 19

Which of the following is a real-life example of a chemical change?

Accepted Answer

Burning wood

Question 20

A scientist observes that when $$10.0\ \mathrm{g} of $$hydrogen reacts with $$80.0\ \mathrm{g} of $$oxygen, $$90.0\ \mathrm{g} of $$water is produced. Which law does this observation support?

Accepted Answer

Law of Conservation of Mass

Introduction to Chemistry: Matter, Scientific Method, and Data Analysis

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