Investigating Physical Properties of Matter
Experiments can be used to investigate the physical properties of matter. But what is matter? Another question would be, what is meant by the term physical properties. Matter is defined as anything that has mass and occupies space. The phrase “occupies space” is self explanatory. Another term for this phrase is volume. Mass on the other hand is defined as a measure of the amount of matter that a substance or object contains.
Physical properties are the ways scientists use to describe matter of any kind. An analogy would be if one asked to describe another person. In giving a description several physical features would be mentioned; such as the person’s height, body build, eye and hair color. So it can be said that physical properties are characteristics of a material. Some examples are: the color of something, its texture, whether or not it has an odor, if it does, what kind of odor, hardness, the object’s mass, volume, and density. (Density is the mass of a material per unit volume of that material.)
During the first two activities of this section air is examined. The question of seeing if air occupies space is looked at first. Following this a comparison of air to another gas is made. In the third activity certain physical properties will be used by students to compare and contrast different materials.
This section begins with assessing the class’s knowledge about air. The students are told the following scenario:
They have received a message from a sister and brother who have been
marooned on a small island somewhere in the Pacific Ocean. They have had no
contact with the world since they were five and six years old. They are now six-
teen and fifteen years of age. Being very intelligent, they have succeeded in
building a communication device in which they can pick up conversations
While they are waiting for help to arrive, they happened to hear a discussion
going on in your classroom about air. The word “air” puzzles them. So they
have sent you a message inquiring about what is air.
Tell the students that their job right now is to spend the next five to ten minutes writing a description of air that can be sent back to the island. Ask for a few volunteers to read their descriptions. As they read, make a list on the board of the properties or characteristics of air that are mentioned. If the fact of air having volume (taking up space) does not come up, bring it up in the form of a question. If it is mentioned, ask the class how can they prove it. This will lead into the first activity designed to show that air takes up space. Students can work in small groups. They are given a five or eight ounce plastic cup (clear is better, but not necessary) and a sheet of paper towel. A source of water deep enough for the cup to be completely submerged is also needed for each group. (It is best if this is done near a sink). Instruct students to ball up the paper towel and insert it into the cup so it won’t fall out. The paper towel should not take up the entire volume of the cup. Demonstrate to the students how to place the cup into the water, as well as how to remove it from the water. The cup should be carefully submerged upside down into the water without tilting the cup in anyway. In other words, the cup should be slowly pushed straight down. After totally submerging the cup, slowly bring it straight up and out of the water; again be careful not to tilt the cup. When the cup is out of the water, dry the outside and bottom rim while it is still upside down. Then have each group remove the paper towel and examine it. The paper towel should be dry. Following clean up, discuss with the class what they observed. Have them give explanations for why the towel was dry. If there where any groups who did not get dry paper towels, tell them you will get back to them. The discussion should be guided to the place of air. No two things can occupy the same place at the same time. Since volume is the amount of space that something takes up (in its simplest definition), this would prove that air has volume.
In the next activity the students again are divided into groups. Each group is given a large paper bag containing two inflated balloons. One balloon contains helium. The other will contain air. Students are not told what each balloon contains; only that each balloon contains a different gas. The contents of each balloon will be compared in two ways. First the groups will drop the balloons at the same time and write down their observations. One should rise (the helium balloon). The other should float to the ground. The second comparison involves observing which balloon will deflate quicker. Balloons will be left in the classroom for four days. Using a string the diameter of each balloon will be measured once a day. Observations can be recorded on the following chart.
BALLOON DIAMETER IN CENTIMETERS
Day 1 Day 2 Day 3 Day 4
On the fourth day the students can answer the following questions:
1. Which balloon deflated faster? How do you know? (Explain your answer).
2. How do you think the gas got out of the balloon?
3. Give an explanation for why one gas escaped faster.
(Hint: It is very similar to why one gas was lighter.)
These questions should lead the class into realizing that the particles that make up the two gases found inside the balloons are different in both mass and size. After going over the questions, the class can be told the identity of the two gases. Summarize the lesson by asking them: “Based on this experiment, how can we compare air and helium?”
Teacher’s note: the helium balloons can be bought at a party store. The balloons used for air should be the same king as the helium balloons and inflated at the same time. (The day before is suggested.) Strings should be attached to the helium balloons for easy management.
Finally during the third activity of this first section, students will examine seven liquids and three powders. They will obtain information about these substances through observation. In describing each liquid, they will take note of color, odor, and viscosity (resistance to flow). When they examine the powders, they will observe texture, color, and shape of the particles that make up the powder. These are the liquids to be used: rubbing alcohol, Kayro syrup, oil , vinegar, hydrogen peroxide, water, liquid dish detergent (preferably yellow in color). The powders are: salt, baking soda, and any type of plain white powdered detergent. Both types of samples have been chosen so that some are very similar in appearance, but differ by their physical properties once one begins to examine them a little further. A small amount of each sample is placed in a clear covered container. (I suggest plastic pert dishes.) The samples are placed on a counter; depending on the size of the class, more than one observation stations may be set up. Students are to record their observations for the previous mentioned properties. A magnifying glass is used to examine the shape of the particles. The students will be tempted to want to identify the materials instead of observing the properties. Emphasize that you are more interested in the description of each item, rather than its identity. Tell the class that they will be told what each sample is at the end of the activity. Once the observations have been made, discuss them. Compare and contrast the properties of the liquids and those of the powders. Point out how the powders all have the same color, but differ in texture, and particle shape. Explain how these kinds of differences are helpful when you are learning about a new substance just discovered or are trying to understand the structure of an object.