Chemistry: Elements, Compounds, and Mixtures Worksheet

Question 1

Classify each sample as an element, compound, or mixture: oxygen gas (O2), water (H2O), salt water, aluminum foil, and trail mix.

Accepted Answer

Oxygen gas is an element because it contains only oxygen atoms. Water is a compound because hydrogen and oxygen are chemically bonded. Salt water is a mixture because salt and water are physically combined. Aluminum foil is an element because it contains aluminum atoms. Trail mix is a mixture because its parts are physically combined and can be separated.

Question 2

A student says, "Carbon dioxide is a mixture because it contains carbon and oxygen." Explain why this statement is incorrect.

Accepted Answer

The statement is incorrect because carbon dioxide is a compound, not a mixture. Its carbon and oxygen atoms are chemically bonded in a fixed ratio, which gives carbon dioxide its own properties.

Question 3

Look at a particle diagram with identical single atoms spread throughout a box. What type of matter does the diagram show, and how do you know?

Accepted Answer

The diagram shows an element because all of the particles are the same type of single atom. There is only one kind of atom present.

Question 4

Look at a particle diagram with identical molecules. Each molecule has one large red atom bonded to two small white atoms. What type of matter does the diagram show, and how do you know?

Accepted Answer

The diagram shows a compound because each molecule contains different kinds of atoms chemically bonded together in the same pattern.

Question 5

A bowl of cereal with milk contains cereal pieces, milk, and fruit slices. Is it a pure substance or a mixture? Explain your answer.

Accepted Answer

It is a mixture because the cereal, milk, and fruit are physically combined. The parts are not chemically bonded and can be separated.

Question 6

Which of the following are pure substances: gold, air, sugar (C6H12O6), vegetable soup, and helium? Explain your choices.

Accepted Answer

Gold, sugar, and helium are pure substances. Gold and helium are elements, and sugar is a compound with a definite chemical formula. Air and vegetable soup are mixtures because they contain different substances physically combined.

Question 7

Table salt has the chemical formula NaCl. What does this formula tell you about table salt?

Accepted Answer

The formula NaCl tells us that table salt is a compound made of sodium and chlorine atoms chemically bonded in a fixed ratio. The ratio is one sodium atom for every one chlorine atom.

Question 8

A sample contains iron filings mixed with sand. Describe one physical method you could use to separate the mixture.

Accepted Answer

A magnet could be used to separate the iron filings from the sand. The iron would be attracted to the magnet, but the sand would not.

Question 9

A clear liquid is made by dissolving sugar in water. Is this a homogeneous mixture or a heterogeneous mixture? Explain your answer.

Accepted Answer

It is a homogeneous mixture because the sugar is evenly dissolved throughout the water. The mixture looks the same throughout.

Question 10

A salad contains lettuce, tomatoes, cucumbers, and cheese. Is it a homogeneous mixture or a heterogeneous mixture? Explain your answer.

Accepted Answer

A salad is a heterogeneous mixture because the different parts can be seen and the composition is not the same throughout.

Question 11

Methane has the chemical formula CH4. Is methane an element, a compound, or a mixture? Explain how you know.

Accepted Answer

Methane is a compound because it contains carbon and hydrogen atoms chemically bonded together. Its formula shows one carbon atom and four hydrogen atoms in each molecule.

Question 12

Air contains nitrogen, oxygen, carbon dioxide, argon, and other gases. Why is air classified as a mixture instead of a compound?

Accepted Answer

Air is classified as a mixture because its gases are physically combined and are not chemically bonded to each other. The amounts of the gases can also vary from place to place.

Question 13

Look at a particle diagram showing two kinds of particles: some single green atoms and some pairs of purple atoms bonded together. The particles are mixed in the same box but are not bonded to each other. What type of matter is shown?

Accepted Answer

The diagram shows a mixture because more than one type of particle is present and the different particles are not chemically bonded to each other.

Question 14

Explain the difference between a compound and a mixture using the words "chemically bonded" and "physically combined."

Accepted Answer

A compound is made of two or more elements that are chemically bonded in a fixed ratio. A mixture is made of substances that are physically combined and can often be separated by physical methods.

Question 15

A teacher gives you three unknown samples. Sample A has only one type of atom. Sample B has two types of atoms bonded in identical molecules. Sample C has several substances that can be separated by filtering. Classify Sample A, Sample B, and Sample C.

Accepted Answer

Sample A is an element because it has only one type of atom. Sample B is a compound because it has different atoms chemically bonded in identical molecules. Sample C is a mixture because it contains substances that can be separated by filtering.

Chemistry: Elements, Compounds, and Mixtures

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