Chemical Formulas and Matter Knowledge Assessment

1. Which of the following best describes an element?

A substance made of two or more different atoms chemically combined

A pure substance made of only one kind of atom

A mixture of two or more substances that can be separated

A substance with uniform composition throughout

An element is defined as a pure substance that consists entirely of one type of atom, which cannot be broken down into simpler substances by chemical means. Each element has unique properties and is represented by a specific symbol on the periodic table. Unlike compounds, which are formed from two or more different atoms chemically combined, or mixtures, which contain multiple substances that can be separated, elements serve as the fundamental building blocks of matter.

Explanation

An element is defined as a pure substance that consists entirely of one type of atom, which cannot be broken down into simpler substances by chemical means. Each element has unique properties and is represented by a specific symbol on the periodic table. Unlike compounds, which are formed from two or more different atoms chemically combined, or mixtures, which contain multiple substances that can be separated, elements serve as the fundamental building blocks of matter.

2. How many atoms of oxygen are in the chemical formula H₂SO₄?

2

3

4

6

In the chemical formula H₂SO₄, each element is represented by a symbol followed by a subscript that indicates the number of atoms of that element in the molecule. The formula consists of 2 hydrogen (H) atoms, 1 sulfur (S) atom, and 4 oxygen (O) atoms. The subscript "4" next to the oxygen symbol (O) indicates that there are four oxygen atoms present in one molecule of sulfuric acid (H₂SO₄).

Explanation

In the chemical formula H₂SO₄, each element is represented by a symbol followed by a subscript that indicates the number of atoms of that element in the molecule. The formula consists of 2 hydrogen (H) atoms, 1 sulfur (S) atom, and 4 oxygen (O) atoms. The subscript "4" next to the oxygen symbol (O) indicates that there are four oxygen atoms present in one molecule of sulfuric acid (H₂SO₄).

3. Salt water is an example of a ____.

Salt water is classified as a homogeneous mixture because it consists of salt (solute) dissolved in water (solvent), resulting in a uniform composition throughout. When salt is fully dissolved, the individual salt particles become indistinguishable from the water, creating a solution where the properties are consistent regardless of where you sample it. This uniformity is a defining characteristic of homogeneous mixtures, distinguishing them from heterogeneous mixtures, where the components remain separate and can be visually distinguished.

Explanation

Salt water is classified as a homogeneous mixture because it consists of salt (solute) dissolved in water (solvent), resulting in a uniform composition throughout. When salt is fully dissolved, the individual salt particles become indistinguishable from the water, creating a solution where the properties are consistent regardless of where you sample it. This uniformity is a defining characteristic of homogeneous mixtures, distinguishing them from heterogeneous mixtures, where the components remain separate and can be visually distinguished.

Submit

4. Which of the following is a compound?

Gold (Au)

Oxygen (O₂)

Water (H₂O)

Nitrogen (N₂)

A compound is a substance formed when two or more different elements chemically bond together. Water (H₂O) is a compound because it consists of two hydrogen atoms bonded to one oxygen atom, resulting in a distinct substance with unique properties. In contrast, gold (Au) is a pure element, while oxygen (O₂) and nitrogen (N₂) are diatomic molecules made up of two atoms of the same element. Therefore, only water qualifies as a compound in this list.

Explanation

A compound is a substance formed when two or more different elements chemically bond together. Water (H₂O) is a compound because it consists of two hydrogen atoms bonded to one oxygen atom, resulting in a distinct substance with unique properties. In contrast, gold (Au) is a pure element, while oxygen (O₂) and nitrogen (N₂) are diatomic molecules made up of two atoms of the same element. Therefore, only water qualifies as a compound in this list.

5. Match each type of matter with its correct description.

Element

Compound

Homogeneous mixture

Heterogeneous mixture

Submit

6. In the chemical formula CO₂, how many total atoms are present in one molecule?

1

2

3

4

In the chemical formula CO₂, there is one carbon atom (C) and two oxygen atoms (O). To find the total number of atoms in one molecule, you simply add these together: 1 (from carbon) + 2 (from oxygen) equals 3. Therefore, one molecule of carbon dioxide contains a total of three atoms.

Explanation

In the chemical formula CO₂, there is one carbon atom (C) and two oxygen atoms (O). To find the total number of atoms in one molecule, you simply add these together: 1 (from carbon) + 2 (from oxygen) equals 3. Therefore, one molecule of carbon dioxide contains a total of three atoms.

7. A heterogeneous mixture has a uniform composition throughout.

True

False

A heterogeneous mixture is characterized by a non-uniform composition, meaning its components are not evenly distributed. This results in distinct, identifiable parts or phases within the mixture, such as in a salad or sand and salt mixture. In contrast, a homogeneous mixture has a consistent composition throughout, where the different substances are indistinguishable from one another. Therefore, the statement that a heterogeneous mixture has a uniform composition is incorrect.

Explanation

A heterogeneous mixture is characterized by a non-uniform composition, meaning its components are not evenly distributed. This results in distinct, identifiable parts or phases within the mixture, such as in a salad or sand and salt mixture. In contrast, a homogeneous mixture has a consistent composition throughout, where the different substances are indistinguishable from one another. Therefore, the statement that a heterogeneous mixture has a uniform composition is incorrect.

8. How many hydrogen atoms are in the chemical formula Ca(OH)₂?

1

2

3

4

In the chemical formula Ca(OH)₂, the hydroxide ion (OH) consists of one oxygen atom and one hydrogen atom. Since there are two hydroxide ions in the formula, you multiply the number of hydrogen atoms in one hydroxide (1) by the total number of hydroxide ions (2). This results in a total of 2 hydrogen atoms in Ca(OH)₂.

Explanation

In the chemical formula Ca(OH)₂, the hydroxide ion (OH) consists of one oxygen atom and one hydrogen atom. Since there are two hydroxide ions in the formula, you multiply the number of hydrogen atoms in one hydroxide (1) by the total number of hydroxide ions (2). This results in a total of 2 hydrogen atoms in Ca(OH)₂.