To view salt under varied magnifications so students can begin to construct the understanding that materials may be composed of parts that are too small to be seen without magnification. To make detailed observations.
At this age, students should have had many opportunities to observe and describe a variety of objects, focusing on the object's physical properties, as well as what the object is made of.
It is now important for students to take such investigations further by observing objects/substances under magnification and recording detailed observations. With magnifiers, students should inspect substances composed of large collections of particles to discover the unexpected details at smaller scales. (Benchmarks for Science Literacy, p. 76.) This discovery prepares them for learning that all matter is made up of atoms, tiny moving parts too small to be seen.
In this lesson, students will predict, observe, and explain the details of salt as they view it under a variety of magnifications. They will observe salt with the naked eye, and then under a hand lens, microscope, and the electron microscope (the electron image is via the Internet). In order to complete this lesson, it is important that students have previous experience working with hand lenses and microscopes.
This sort of detailed observation provides an opportunity for students to keep written records of their discoveries and analyze the collected data. As part of the process of recording and discussing observations, students will be required to make predictions and note differences.
Pour some salt into the palm of your hand and walk around the room allowing students to view it without saying anything. You may use table, sea, or kosher salt for this activity. However, you may want to use sea salt or kosher salt as the crystals are a little larger in this form.
Once all students have observed the substance, ask the following questions:
- What do you think the substance in my hand is?
- Does this salt look different than the salt used in your home? If so, how?
Explain to students that salt can be processed naturally, such as sea salt, or it can be processed in a factory where chemicals are added for various reasons. Continue with questioning:
- Where do you find salt? How is it used? (Most students will say on food or in cooking, but lead them to other uses, e.g., on slippery roads, in the ocean/sea, curing meat.)
- How would you describe salt? (Responses should include shape, color, odor, etc.)
- How many of you have ever looked at salt using a hand lens or under a microscope?
Then ask students to think about what salt crystals might look like when magnified. Encourage them to think about the shape and texture. Then explain to students that they will look at salt under different magnifications and record their observations.
In this activity, students examine salt under successive magnifications. Students will record their observations on the Science NetLinks student sheet, Salt: Up Close and Personal.
There are many ways to structure this activity depending on your students' needs, class size, and available equipment. The following model is for small groups and centers through which students could rotate. The centers could be set up as follows:
- Center 1: The Naked Eye--a teaspoon of salt on a piece of black construction paper.
- Center 2: Hand Lens--a teaspoon of salt on a piece of black construction paper, and a hand lens.
- Center 3: Microscope--a smaller amount of salt, a microscope, a slide, and a cover slip.
- Center 4: Electron Microscope--students will visit the Science Learning Network website and look at an image of kosher salt.
Information About the Electron Microscope:
If you would like a better understanding of how an electron microscope works, Science Learning Network has a section devoted to How the SEM Works. The difference between a regular microscope (light) and a scanning electron microscope is that the light microscope uses light waves to magnify the image and the electron microscope uses electrons. The electron microscope shows images in black and white but can reach higher magnifications and show more details than the light microscope.
Distribute and go over the student sheet: Salt: Up Close and Personal. Tell students that they will look at salt using different equipment and magnifications, and then record their findings. Encourage students to make detailed observations, descriptions, and drawings on this sheet. For example, they should use geometric shapes as they make and record observations; i.e., they should describe salt in the shape of a diamond, square, etc., rather than simply saying "it is dots."
Let students know they will discuss their observations with the class. Also encourage them to be independent thinkers and not use other students' work.
Before beginning the activity, have students make predictions about what salt will look like when magnified, and record their predictions in the appropriate area on the student sheet. Again, these should be as detailed and descriptive as possible. Then have students make their observations and complete the student sheet.
When all students have finished observations, ask the following questions:
- Why was it important for you to make a prediction? (e.g., So I could have a record of my thoughts, and be more sure of how they changed over time.)
- How did your predictions compare with what you actually observed about the structure of salt? (e.g., The salt really looked like little squares/crystals. The salt was clear rather than white.)
- How were the salt crystals the same under the magnifying glass and electron microscope? How were they different? (Students' responses should focus on the details of the shape and structure.)
The discussion continues but the focus shifts to the record keeping. Students should recognize how recording observations made it easier to compare and analyze the physical details of salt.
- What was the most interesting difference noticed with each magnification?
- How did the data sheet help you with this activity? (Answers will vary.)
- Were there any other items that we could have added to the data sheet to make recording observations easier or more complete? (Answers will vary.)
Once the discussion is finished, collect the student sheets and evaluate them appropriately. Students should have described the salt in written and drawn form, using as much detail as possible. There should be notable differences between their descriptions at successive magnifications, as well as written comparisons for each magnification.
Students can investigate more images from Science Learning Network. This website allows students to look at toilet paper, and scratch and sniff paper under an electron microscope. Have students compare how paper looks under a magnifying glass, or seen normally. Students can either draw or explain the difference between these.
Students can check out the book Dirt and Grime, Like You've Never Seen, by Vicki Cobb. They could write a brief summary about what was new or surprising about particles of dirt, grime, and other items made up of parts.