Substances, Mixtures, and Solubility - Mr. Mesic's Science Classes

[Pages:43]Substances,

Matter can be classified as a substance (element or compound) or a mixture (homogeneous or heterogeneous).

SECTION 1

What is a solution?

Main Idea Solutions are homogeneous mixtures that can be solids, liquids, or gases.

SECTION 2

Solubility

Main Idea Solubility refers to the amount of a solute that can dissolve in a solvent at a given temperature and pressure.

SECTION 3

Acidic and Basic Solutions

Main Idea When dissolved in water, acids produce hydronium (H3O) ions, and bases produce hydroxide (OH) ions.

Mixtures, and Solubility

Big-Band Mixtures

It's a parade and the band plays. Just as the mixing of notes produces music, the mixing of substances produces many of the things around you. From the brass in tubas to the lemonade you drink, you live in a world of mixtures. In this chapter, you'll learn why some substances form mixtures and others do not.

Science Journal Find and name four items around you that are mixtures.

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Start-Up Activities

Particle Size and Dissolving Rates

Why do drink mixes come in powder form? What would happen if you dropped a big chunk of drink mix into the water? Would it dissolve quickly? Powdered drink mix dissolves faster in water than chunks do because it is divided into smaller particles, exposing more of the mix to the water. See for yourself how particle size affects the rate at which a substance dissolves.

1. Pour 400 mL of water into each of two 600-mL beakers.

2. Carefully grind a bouillon cube into powder using a mortar and pestle.

3. Place the bouillon powder into one beaker and drop a whole bouillon cube into the second beaker.

4. Stir the water in each beaker for 10 s and observe.

5. Think Critically Write a paragraph in your Science Journal comparing the color of the two liquids and the amount of undissolved bouillon at the bottom of each beaker. How does the particle size affect the rate at which a substance dissolves?

Solutions Make the following Foldable to help classify solutions based on their common features.

STEP 1

Fold a vertical sheet of paper from side to side. Make the front edge about 1.25 cm shorter than the back edge.

STEP 2 Turn lengthwise and fold into thirds.

STEP 3 Unfold and cut only the top layer along both folds to make three tabs.

STEP 4 Label each tab as shown.

Solid

Liquid Gaseous

Solutions Solutions Solutions

Find Main Ideas As you read the chapter, classify solutions based on their states and list them under the appropriate tabs. On your Foldable, circle the solutions that are acids and underline the solutions that are bases.

Preview this chapter's content and activities at bookl.

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Learn It! A cause is the reason something happens. The

result of what happens is called an effect. Learning to identify causes and effects helps you understand why things happen. By using graphic organizers, you can sort and analyze causes and effects as you read.

Practice It! Read the following paragraph. Then use the

graphic organizer below to show what might happen when a solution is cooled.

Under certain conditions, a solute can come back out of solution and form a solid. This process is called crystallization. Sometimes this occurs when the solution is cooled or when some of the solvent evaporates. Crystallization is the result of a physical change.

-- from page 66

Effect

Cause Effect

Effect

Apply It! As you read the

chapter, be aware of causes and effects of dissolving. Find at least one cause and its effect.

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Use this to focus on the main ideas as you read the chapter.

Before you read the chapter, respond to the statements below on your worksheet or on a numbered sheet of paper. ? Write an A if you agree with the statement. ? Write a D if you disagree with the statement.

Graphic organizers such as the Cause-Effect organizer help you organize what

you are reading so you can remember it later.

After you read the chapter, look back to this page to see if you've changed your mind about any of the statements. ? If any of your answers changed, explain why. ? Change any false statements into true statements. ? Use your revised statements as a study guide.

Before You Read A or D

Statement

Print out a worksheet of this page at bookl.

1 Only a chemical process can change one substance into one or more new substances.

2 Fruit drink is an example of a substance.

3 Brass, a type of metal, is an example of a solution.

4 The solubility of a solute in a solvent varies with temperature.

5 A solute that dissolves quickly is more soluble than one that dissolves slowly.

6 You can increase the solubility of a solute by stirring it in the solvent.

7 Concentration is a measure of how much solute is dissolved.

8 A strong acid is one that is concentrated.

9 The more hydrogen atoms an acid contains, the stronger it is.

After You Read A or D

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What is a solution?

Distinguish between substances and mixtures.

Describe two different types of mixtures.

Explain how solutions form. Describe different types of

solutions.

The air you breathe, the water you drink, and even parts of your body are all solutions.

Review Vocabulary

proton: positively charged particle located in the nucleus of an atom

New Vocabulary

substance

? heterogeneous mixture

? homogeneous mixture

? solution

solvent

?? ?? solute

precipitate

Substances

Water, salt water, and pulpy orange juice have some obvious differences. These differences can be explained by chemistry. Think about pure water. No matter what you do to it physically--freeze it, boil it, stir it, or strain it--it still is water. On the other hand, if you boil salt water, the water turns to gas and leaves the salt behind. If you strain pulpy orange juice, it loses its pulp. How does chemistry explain these differences? The answer has to do with the chemical compositions of the materials.

Atoms and Elements Recall that atoms are the basic build-

ing blocks of matter. Each atom has unique chemical and physical properties which are determined by the number of protons it has. For example, all atoms that have eight protons are oxygen atoms. A substance is matter that has the same fixed composition and properties. It can't be broken down into simpler parts by ordinary physical processes, such as boiling, grinding, or filtering. Only a chemical process can change a substance into one or more new substances. Table 1 lists some examples of physical and chemical processes. An element is an example of a pure substance; it cannot be broken down into simpler substances. The number of protons in an element, like oxygen, are fixed--it cannot change unless the element changes.

Table 1 Examples of Physical and Chemical Processes

Physical Processes

Chemical Processes

Boiling

Burning

Changing pressure

Reacting with other chemicals

Cooling

Reacting with light

Sorting

Compounds Water is another example of

a substance. It is always water even when you boil it or freeze it. Water, however, is not an element. It is an example of a compound which is made of two or more elements that are chemically combined. Compounds also have fixed compositions. The ratio of the atoms in a compound is always the same. For example, when two hydrogen atoms combine with one oxygen atom, water is formed. All water--whether it's in the form of ice, liquid, or steam--has the same ratio of hydrogen atoms to oxygen atoms.

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