Physical Properties of Matter. Examples of Physical Properties. QUESTION: How could you find the volume of air in an "empty" room?

Transcription

1 QUESTION: How could you find the volume of air in an "empty" room? The volume of regularly shaped solids can be calculated from their dimensions. For example, the volume of a rectangular solid is the product of its length, width, and height (l w h). The SI unit for solid volumes is cubic meters (m 3 ) or cubic centimeters (cm 3 ). For irregularly shaped solids the water displacement method is used to measure volume. You can see how it works in the figure below and in the video below. Physical Properties of Matter. Matter has many properties. Properties are characteristics that describe matter. Physical properties -(properties of matter that can be measured or observed without matter changing the substance) are typically things you can detect with your senses. For example, whether a given substance normally exists as a solid, liquid, or gas is a physical property. Consider water, it is a liquid at room temperature, but frozen water (ice) is still water. Generally, physical properties are things you can see, smell, taste, or feel. Examples of Physical Properties 19

2 Physical properties include the phase of matter and its color and odor. For example, oxygen is a colorless, odorless gas. Chlorine is a greenish gas with a strong, sharp odor. The physical properties of oxygen gas are colorless and odorless while the physical properties of chlorine gas are green and stinky. Other physical properties include hardness, freezing and boiling points, the ability to dissolve in other substances, and the ability to conduct heat or electricity. Can you think of other physical properties? Density Density-(amount of mass in a given volume)- is a physical property of matter. It is defined as a substance s mass per unit volume. It reflects how closely packed the particles of matter are. Density is calculated from the amount of mass in a given volume of matter, using the formula: and a volume of 10 ml? PROBLEM: What is the density of a substance that has a mass of 20 g SOLUTION: PROBLEM: An object has a mass of 180 kg and a volume of 90 m 3. What is its density? SOLUTION: You Try It! To better understand density, think about a bowling ball and a volleyball. The bowling ball feels heavy. It is solid all the way through. It contains a lot of tightly packed particles of matter. In contrast, the volleyball feels light. It is full of gasses. It contains fewer, more widely spaced particles of matter. Both balls have about the same volume, but the bowling ball has a much greater mass. Its matter is more dense. 20

3 Density is not the only physical property of matter. Here are some additional physical properties. 21

4 Chemical Properties of Matter Some properties of matter can be measured or observed only when matter undergoes a change to become an entirely different substance. These properties are called chemical properties (properties that describe the ability of a substance to undergo a specific chemical change)-they include flammability-(ability to ignite)- and reactivity (ability to participate in a chemical reaction). Flammability Flammability is the ability of matter to ignite. Wood is flammable. When wood burns, it changes to ashes, carbon dioxide, water vapor, and other gases. After burning, it is no longer wood. Reactivity Reactivity is the ability of substances to undergo chemical reactions and release or absorb energy either by reacting with themselves or with other materials. For example, iron is highly reactive with oxygen. When it combines with oxygen, it forms the reddish powder called rust. Rust is not iron but an entirely different substance, iron oxide, that consists of both iron and oxygen. The iron in this steel chain has started to rust. 22

5 Lesson Summary Matter is anything that has mass and volume. Mass is the amount of matter in a substance. Volume is the amount of space matter takes up. Matter has both physical and chemical properties. Physical properties can be measured or observed without matter changing to a different substance. Chemical properties of matter can be measured or observed only when matter undergoes a change to become an entirely different substance. Think Like A Chemist Recall 1. What is matter? 2. Label each property as either Physical (P) or Chemical (C). Density Hardness Flammability Mass Volume Reactivity odor freezing point Apply Concepts 3. Create a table listing two physical and two chemical properties of iron. Physical Chemical 4. Using your knowledge of salt dissolving in water, explain why the ability to dissolve is a physical property and not a chemical property? Think Critically 5. Some kinds of matter are attracted to a magnet. Is this a physical or chemical property of matter? How do you know? 23