Summary

In this lesson, students learn that the particles that make up matter are in constant motion. The concepts that matter is made of invisible particles and that these particles are in constant motion can be difficult for students to comprehend. Although this motion isn’t noticeable on a daily basis, the results of this motion can be observed.

In Part A, students interact with an online simulation to compare the ways that atoms and molecules move in solids, liquids, and gases. In Part B, to further understand one aspect of particle motion, students design an investigation to examine the dissolving of sugar as a function of the temperature of the water. To collect quantitative data for this investigation, students learn about what it means for a substance to dissolve as they witness the process of dissolving.

Standards

NGSS and Cross-Disciplinary Extensions addressed in this lesson

Objectives

By the end of this lesson, students should be able to:

• Explain that matter is composed of extremely small particles, which are constantly moving.
• Describe the three states of matter.
• Compare how particles move in solids, liquids, and gases.
• Investigate the effect of water temperature on the solubility of a sugar cube in water.
• Measure, record, graph, and analyze quantitative data.
• Communicate investigation findings.

Chemistry Topics

This lesson supports students’ understanding of the following topics in chemistry:

• States of matter
• Solutions
• Reaction rate
• Solubility

Time

Teacher Preparation for Explore Part 2: 45 minutes to prepare amounts of water at different temperatures

Lesson: (times are approximate)

• Engage Part A: 45 minutes; optional video: 23 minutes
• Explore Part A: 45 minutes
• Explain Part A: 45 minutes
• Engage Part B: 20 minutes
• Explore Part B: 2 × 45 minutes
• Explain Part B: 45 minutes

Materials

Part A Engage

For each group:

• Small container of water

For each pair of students:

• Aluminum foil (approximately 10 cm × 10 cm)
• Scissors
• Tweezers
• Hand lens

Part A Explore

• Computer with Internet access for each student or pair of students
• Science journal for each student

Part B Explore

For teacher demonstration:

• Small object to weigh (e.g. small pencil, paper clip, crumpled sheet of paper)
• Scale or balance

For each group:

• Sugar
• Plastic cup
• Plastic spoons or stir sticks
• Water of different temperatures
• Thermometer
• Stopwatch or clock
• Measuring cup or graduated cylinder
• Science journal, each student

For the class:

• Refrigerator or ice
• Hot plate
• Containers to hold water, about 2 liters in size
• Cloth towels for water spills
• Bucket or sink for disposal of water

Safety

• Students should not taste any water (unless directed to by the teacher).
• Caution students to be careful if any water spills on the floor and to clean up spills immediately to avoid accidents.

Vocabulary Terms

• dissolve
• gas
• liquid
• solid
• solubility
• solute
• solution
• solvent

Keywords

particle model, dissolve, atom, molecule, state of matter, solution, solubility

Teacher Notes

Science Background

All matter is made up of very tiny particles that are in constant motion, and these particles are attracted to one another. The temperature of a substance is related to the average kinetic energy of its particles; the faster the particles move, the higher the temperature of the substance.

One ramification of this behavior of particles is the dissolving of sugar in water. If sugar is as added to water, the water molecules come into contact with the sugar molecules. This results in the sugar dissolving in the water. The warmer the water, the faster the water molecules move, and the water molecules will strike the sugar molecules more frequently. As a result, more of the sugar will dissolve in hot water than in cold water in a given amount of time

The following websites provide additional information about the concepts discussed.

• Why Does Water Dissolve Sugar? (American Chemical Society)
• Chemistry Review (American Chemical Society)
• Particle Theory (University of Leicester)
• Solubility (Chemistry Information Site)

Design of the Lesson

The lesson is divided into two parts, each of which contains an Engage, Explore, and Explain section. Part A deals with the particle model of matter and utilizes an online simulation to model the behavior of particles in a solid, liquid, and gas. Part B engages students in a hands-on investigation that lends credence to the particle model. After both parts, the lesson concludes with an Elaborate and Evaluate section. The lesson can be taught over a period of four or five days, with different lengths of class periods if needed.

Design of the Investigation & Tips

It would be best if students are given the freedom to design their own investigation for the Engage Part B section: looking for a relationship between the time to dissolve and the temperature of the water. A design that can work for groups and a whole class would be the following:

Think about how you want to organize and distribute the different temperatures of water. You might want to consider using picnic or foam coolers to keep the water from changing temperature quickly once you’ve prepared it. Have a towel or two available for any spills. Have a sink or bucket ready for disposal of the sugar solutions. You should discuss with students what it means for the sugar to “dissolve”, so every group uses the same standard or definition.

1. Label 3 clear plastic cups “Cold”, “Hot”, and “Room Temp.” for each group Prepare ice water, room temperature water, and hot water. Place ¼ cup of each temperature of water into its labeled cup. You could have students assist with this preparation.
2. Give each group of students the three cups of water at different temperature's
3. Place ½ teaspoon of sugar in each cup at the same time and swirl the cups.
4. Watch closely to see when all the sugar dissolves in any one of the cups. When the sugar completely dissolves in one of the cups, stop swirling all of the cups.
5. Look at the bottom of the cups. One cup will have no undissolved sugar at the bottom. Try to tell which of the other two cups has the most sugar left in the bottom.
6. In the chart, record which temperature of water dissolved all the sugar, which dissolved the least, and which was in between.
7. There may be some uncertainty about how much sugar is dissolved or left undissolved at the bottom of the cup. But if there is a great enough difference in temperature between the hot and ice water, the difference should be obvious.

Lesson

Part A - Engage

Students access prior knowledge of the differences between solids, liquids, and gases.

Give each small group of students a bottle or similar container of water to observe. Ask them to share their observations within the group. They should record their observations. Gather students back together as a class and discuss each group’s observations. Continue the discussion about water by asking: What is this liquid water made of? Can you describe what makes it up? If you could imagine or even see this water up close at a very tiny scale, how would it behave? Probe students’ ideas about the particulate nature of matter, but don’t tell them the accepted scientific view.

Don’t dwell on this for long, but continue the discussion by asking: What will happen to this water if you put it in a freezer for several hours? What properties would this substance have? What will happen to this water if you put it in a pan and boil it for several minutes? What properties would this substance have then? Continue the discussion about the different states of matter by asking students: Do the particles (or whatever term the class uses to talk about the makeup of water) that make up liquid water change at all when water freezes or boils? If they do change, how do they change?

Have a discussion so that students can think about what size these particles are, what they might look like, and how many there are. and how they are arranged.

To involve students in a physical activity, pair them with a partner to cut a piece of aluminum foil in half. Take one of the pieces, cut it in half again and continue this process. Offer each pair some tweezers and a magnifying glass as a way of hinting that these pieces are going to get very very small. At some point, ask:
Can you keep going like this forever? How small would the pieces be? Will they still be made of aluminum when you get them invisibly small?

Ask students to imagine being shrunk to the size of a particle. What would water particles and aluminum particles look like? Encourage students to describe and sketch both types of particles. Would both types of particles look the same? If not, how would they differ? How would a group of particles of ice look compared to a group of particles of liquid water; compared to a group of particles of water as a gas? What would particles of aluminum look like? Provide time for students to work on this task, and then allow them to share their ideas with the class.

An option at this point is to show students the video Bill Nye the Science Guy – Atoms and Molecules, about 23 minutes long. Using a very entertaining style, this video reinforces the concepts of:

• the composition of matter (all matter is made of atoms)
• the structure of atoms and molecules
• the small size of fundamental particles

(It also includes concepts that are not addressed in this lesson but may be important for your class: the variety of atoms that make up different substances; the components of the nucleus; the idea that all living organisms are based on the carbon atom.)

Tell students they are going to have a number of opportunities in this lesson to explore and learn more about what water is like as a solid, liquid, and gas, and how the particles that make them behave on a very small scale (too small to see under a typical microscope).

Download the Teacher Guide to view the rest of this lesson.