In this lesson, students learn that 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 time it takes to dissolve a sugar cube in water 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 and they witness the process of the term “dissolve.”
NGSS and Cross-Disciplinary Extensions addressed in this lesson
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.
This lesson supports students’ understanding of the following topics in chemistry:
- States of matter
- Quantitative chemistry
- Reaction rate
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
Part A Engage
For each group:
- Small container of water
For each pair of students:
- Aluminum foil (approximately 10 cm × 10 cm)
- 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 cubes
- Plastic cup
- Plastic spoons or stir sticks
- Water of different temperatures
- Thermometer, metric
- 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
- 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.
particle model, dissolve, atom, molecule, state of matter, solution, solubility
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 (in general, an object with a greater speed equates to greater kinetic energy).
One ramification of this behavior of particles is the dissolution of a sugar cube in water. If a sugar cube is submerged in a liquid such as water, the water molecules will come into contact with the sugar molecules. This results in the sugar cube 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 cube will dissolve in warm 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:
- Prepare three to five samples of water at different temperatures. Use ice, a refrigerator, and a hot plate to help raise or lower room temperature water. Ideally, each group will have three samples of water at different temperatures. You could have students assist with this preparation.
- You should discuss with students what it means for the sugar cube to dissolve, so every group uses the same technique. See the narrative below in Explore Part B on developing an “operational definition.” You might find you can use this concept in other activities and curricula.
- 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-water solutions.
- Reasons for why the investigation may not have work as planned: There may be some uncertainty of when the sugar cube “dissolves” or there might not be much difference in temperatures among samples by the time groups receive their water so students may not measure significant time differences for dissolving times. One way to handle this is to collect the time and temperature data from each group (assuming each group had all the different water temperatures), organize the data on the board, and find the average time for each water temperature. Students could then use the average time-to-dissolve vs. temperature as the data to graph and analyze.
- The online simulation States of Matter: Basics has an accompanying tip for teachers. Both the simulation and teacher tips provide more advanced content than you will probably want to use with your students. Use the parts that you feel are most appropriate for your students.
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 in their science journals. 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? How would it act? 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? Can students tell you what size these particles are? What they might look like? How many are they?
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 use their science journals 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).