Lesson 5: Pure Substances and Mixtures

Questions and Answers

Is distilled water a mixture or a pure substance?

Mixture

Pure substance (correct)

Is rainwater a pure substance or a mixture?

Mixture (correct)

Pure substance

Do two compounds form a mixture or a pure substance when you put them together mechanically?

Mixture

How could you separate a mixture of sand and water?

Allow sand to settle and drain off the water or use a filter. Signup and view all the answers

What are some examples of chemical changes?

Burning wood, rusting iron, dissolving metal in acid. Signup and view all the answers

What do you call separating water into its component elements, hydrogen and oxygen?

Electrolysis Signup and view all the answers

What are some examples of homogeneous mixtures?

Iced tea, soda without bubbles, salt water, coffee, vinegar. Signup and view all the answers

What are some examples of heterogeneous mixtures?

Salad dressing, vegetable soup, pizza. Signup and view all the answers

Are colloids homogeneous or heterogeneous?

Heterogeneous Signup and view all the answers

What are some examples of colloids that include a gas and a liquid?

Fog, mist, aerosols. Signup and view all the answers

What is a pure substance?

An element or compound that cannot be separated by physical changes. Signup and view all the answers

Why aren't powdered mix drinks or saltwater pure substances?

They are mixtures. Signup and view all the answers

How is a colloid different than a suspension?

Colloid particles do not settle out. Signup and view all the answers

What are some examples of colloids that include a gas and a solid?

Smoke, smog, air pollution. Signup and view all the answers

What are some methods for physically separating a mixture?

Straining, filtering, magnetizing, settling. Signup and view all the answers

What is the definition of a compound?

A substance made up of atoms or ions of two or more different elements joined by chemical bonds. Signup and view all the answers

Why is hydrogen a pure substance?

Because it is an element. Signup and view all the answers

Why is salt a pure substance?

Because it is a chemical compound. Signup and view all the answers

Study Notes

Pure Substances vs. Mixtures

Distilled water is a pure substance, consisting of only hydrogen and oxygen; it contains no impurities like salts or silt.
Rainwater, while derived from pure water vapor, is a mixture due to tiny dust particles it collects as it falls.

Mixtures

When two compounds are mechanically combined, such as by stirring, they form a mixture rather than a pure substance.
Sand and water can be separated by allowing the sand to settle and then draining the water, or by filtering the mixture.

Chemical Changes

Common examples include burning wood, rusting iron, and dissolving metals in strong acids, indicating transformation of substances.

Separation Processes

Electrolysis is a method that separates water into hydrogen and oxygen using electric current.
Mixtures can also be physically separated by methods such as straining, filtering, magnetizing, and allowing components to settle.

Homogeneous and Heterogeneous Mixtures

Homogeneous mixtures are uniform throughout; examples are iced tea, soda without bubbles, saltwater, coffee, and vinegar.
Heterogeneous mixtures have visible components; examples include salad dressing, vegetable soup, and pizza.
Colloids, although heterogeneous, do not allow their particles to settle out.

Colloids

Examples of colloids containing a gas and liquid are fog and mist; aerosols like hairspray contain chemicals and a gas propellant.
Colloids containing a gas and solid include smoke, smog, and air pollution, which consist of small particles suspended in air.

Definitions and Characteristics

A pure substance is defined as an element or compound that cannot be separated by physical changes.
Powdered drink mixes and saltwater are considered mixtures because they do not consist of a single element or compound.
A compound is formed when atoms or ions of different elements are chemically bonded.
Hydrogen and salt are pure substances: hydrogen as an element and salt as a chemically bonded compound, separable only through chemical processes.

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Description

Test your knowledge of pure substances and mixtures with this flashcard quiz. Explore the definitions and examples of distilled water and rainwater to better understand their classifications. Perfect for students studying chemistry concepts related to mixtures.