Before Strategy/Engage: 15 minutes
1. The teacher should give the students two minutes to respond to this quick write prompt: "How can you distinguish one substance from another substance?"
2. After the students write their answers individually, the teacher should allow students two minutes to discuss their answers with a partner or group. The students should record any new ideas on their list.
3. After students discuss their answers, the teacher should ask student volunteers for their responses and create a class T-chart, labeled "Physical Properties" on the left and "Chemical Properties" on the right. As students share their responses, the teacher should add each idea on the appropriate side of the chart.
Note: Physical properties can be determined by observing a substance without changing its composition. Examples of physical properties include color, solubility, freezing point, and boiling point. Chemical properties are determined by the substance's reaction to other substances or other chemical changes. Examples of chemical properties include reactivity with other substances, flammability, and chemical stability.
During Strategy/Explore & Explain: 30 minutes
1. Next, the teacher should tell the students that they will need to plan an investigation to test how one substance could be distinguished from another substance based on its characteristic properties. Depending on the students' experience in planning investigations, the teacher may give the students free reign to plan the investigation with their group members or guide students to plan an investigation similar to the one detailed in the remainder of the lesson plan.
2. Before beginning the investigation, the students will need to plan each step of the scientific experiment, which includes the following:
- The problem or question that the experiment will attempt to answer
- A hypothesis that describes what the students think will occur in the investigation (usually formatted as an If...then...because... statement)
- The materials that will be needed to carry out the investigation
- An experimental design that describes the variables in the investigation and the procedures that will be followed to complete the experiment
- A plan to collect data such as a chart, table, or graph
The students can write this information on notebook paper or use a planning sheet, such as "Scientific Method Flow Chart" from biologycorner.com.
After Strategy/Explain & Elaborate: 60 minutes
Note: The following procedures are an example of a scientific investigation that will meet the objectives of the selected standard. Depending on the experiment the students planned in the during strategy, the specifications of each individual experiment may vary.
1. Students should be divided into collaborative groups of approximately four students each. The teacher should give each student a copy of the "Mystery Substance Data Table" (see attachments). Each group of students will need the required materials to carry out the scientific investigation.
2. The students should begin by observing the five mystery substances and recording the color, relative particle size (using a magnifying glass, if needed), and state of matter of each substance on their data table.
3. The students should test each mystery substance for magnetic properties. The students should place one scoop of the mystery substance on a sheet of paper, then move the magnet underneath the paper (the magnet should not directly touch the mystery substance). Students should record findings in their data table (magnetic or not magnetic). Complete this procedure for all mystery substances.
4. The students should use a graduated cylinder to measure 5 mL of water. The students should pour the 5 mL of water into a clean test tube, then place one scoop of the mystery substance into the test tube with the water. The students can swirl the test tube to mix the substance with the water or use a stirring rod. Students should record their findings in the data table (insoluble, partially soluble, or soluble). Complete this procedure for all mystery substances.
5. The students should use a graduated cylinder to measure 5 mL of vinegar or acetic acid. The students should pour the 5 mL of the selected acid into a clean test tube, then place one scoop of the mystery substance into the test tube with the water. The student can swirl the test tube to mix the substance with the selected acid or use a stirring rod. Students should record their findings in the data table (if the substance reacts with the acid, the students should describe the appearance of the reaction). Complete this procedure for all mystery substances.
6. After all groups complete the investigation, the teacher should ask the students to respond to the following questions, which will serve as the conclusion of their scientific investigation. The teacher may wish for the students to respond verbally and discuss their answers with their groups or to write their answers on paper for the teacher to review at the conclusion of the lesson.
- Did your investigation fully answer the question you developed prior to the experiment? Would you need to perform any additional tests to answer your question?
- How could you use the data collected during this investigation to determine the identity of the mystery substances?
- Are you able to identify any of the mystery substances based on the physical and chemical properties discovered during the investigation? If you were not able to determine the identity of a particular mystery substance, what additional tests would you need to perform to discover the substance's identity?