physical and chemical changes: Martian Fuel
Source: This laboratory was adapted and modified from:
Benchmarks:
SC.5.P.9.1 Investigate and describe that many physical and chemical changes are affected by temperature.
SC.4.P.9.1 Identify some familiar changes in materials that result in other materials with different characteristics, such as decaying animal or plant matter, burning, rusting, and cooking.
SC.3.P.9.1 Describe the changes water undergoes when it changes state through heating and cooling by using familiar scientific terms such as melting, freezing, boiling, evaporation, and condensation.
SC.5.N.2.1 Recognize and explain that science is grounded in empirical observations that are testable; explanation must always be linked with evidence.
Objective/Purpose:
- Students will conduct a series of experiments to learn the difference between physical and chemical changes.
- Students will describe how some familiar changes in materials result in other materials with different characteristics.
Background Information:
A "phase" describes a physical state of matter. The key word to notice is physical. Things only move from one phase to another by physical means. If energy is added (like increasing the temperature) or if energy is taken away (like freezing something), you have created a physical change.
When a physical change occurs, the material keeps its identity. For example, when the temperature falls below freezing, water in a pond changes from a liquid to a solid. The water hasn’t changed what it is. It is still water. It just changed to another form. Changing from one form to another without turning into a new substance is an example of a physical change; many physical changes can be undone by physical means. Physical changes can include changes in position, size, shape, volume, and phase of matter.
In contrast, a chemical change occurs when one substance or kind of matter changes into another completely different kind of matter with different properties. For instance, if you leave an iron nail outdoors long enough, it will rust. Rust is not iron. It is a new substance made of iron and oxygen. Changing into a new substance with different properties is an example of a chemical change; cannot be undone by physical means. Example: burning of wood produces ash and smoke, which have different properties than wood.
Teacher Notes:
Introduce the activity by asking several of the students to read aloud the situation given at the beginning of the worksheet (below). The scenario is that the class has landed on Mars on a rocket but needs to create more fuel to return to Earth. The only way to create fuel is to try to create an entirely new substance from materials on board. This background scenario will create interest in the activity and provide continuity between the individual experiments.
Divide students into small groups (3 - 4 students). Instruct the students that goggles must be worn at all times. Remind students that although they will use some food items in the lab, they may not eat, drink, or taste anything. Review the difference between chemical and physical properties. The worksheet will guide students through the experiments. The relative amounts of materials have been adjusted to minimize messiness, but it is suggested that the a experiments be conducted with a lab tray (a minimum of two physical and two chemical labs from below should be set up for students to complete, adjust materials and scenario to labs chosen).
Students should recognize that breaking the antacid tablet and Play-doh into small pieces are physical changes because no new substances are formed. The melting of ice is also a physical change because it involves only a change of state and the substance is still water.
Students should also recognize that chemical properties are only observable during a chemical reaction. Chemical changes (reactions) result in formation of a new substance, while physical changes do not.
Engage: Present the following scenario:
Imagine that we are the first group of astronauts to land on Mars. Our space ship’s fuel tanks were lost during landing. Some friendly Martians have offered to help us make fuel. However, Mars doesn’t have the ingredients to make the type of fuel that is used on Earth. The Martians have told us that none of the substances that we have on our ship right now can be used as rocket fuel, but we might be able to fuel the rocket by creating an entirely new substance from supplies we already have. All that we have to work with are some supplies from our ship’s first-aid kit and food stores, including antacid, baking soda, lemon juice, vinegar, milk, Kool-Aid powder, ice, and Play-doh.
Materials:
Safety gogglesPlay-doh
Graduated cylindersBaking soda
Small plastic cupsLemon juice
Paper towelsVinegar
IceMilk
Antacid tabletsKool-Aid powder
Explore:
You will do several experiments today. To prevent spills, keep the cups on a tray and pour your ingredients. Keep your goggles on at all times. As you observe the changes that occur during the experiments, your goal is to decide which changes are chemical and which changes are physical. Ask students to identify some clues that could suggest that a chemical reaction has occurred (generation of heat, drop in temperature, precipitate formation, gas production, a new odor, new color etc.).
Be sure to fill out the group data sheet with observations of the ingredients before, during, and after they undergo physical or chemical change. When you are done with all of the experiments, you should answer the follow up questions on the last page.
Experiment Station Labels (located at the end of Teacher version)
Experiment Station Procedures:Experiment A-1: Antacid tablet
1. Observe and describe the antacid tablet at your table.
2. Break the tablet into small pieces. Is this a physical or chemical change?
Experiment A-2: Broken Antacid pieces
3. Using a graduated cylinder, measure 50 mL of water and add it to a cup. Drop the tablet pieces into the cup.
4. Observe what happens and write whether it is a physical or chemical change on theobservation form.
Experiment B-1: Ice
1. In the empty clean cup, place 1 ice cube. Observe and record how the ice looks and feels.
2. Set the cup and ice cube aside until you are finished with the B-2 experiments.
Experiment B-2: Play-doh
1. Remove the Play-dohfrom its container and describe how it looks, feels, and smells.
2. Break the Play-doh up into many small pieces.
3. Observe and record the change.
4. On the data sheet, write whether this is a physical or chemical change.
Go back to Experiment B-1: Ice
1. Look at the cup that held the ice cube from experiment B-1.
2. Observe and record the change.
3. On the data sheet, write whether this is a physical or chemical change.
Experiment C: Baking soda and lemon juice
1. Using a graduated cylinder, measure 40 mL of lemon juice and add it to a small jar.
2. Add 1 teaspoon of baking soda to the jar.
3. Observe and record the changes.
4. On the data sheet, write whether this is a physical or chemical change.
Experiment D: Baking soda and vinegar
1. Add 1 teaspoon of baking soda to a cup.
2. Using the graduated cylinder, measure 10 mL of vinegar and add it to the same cup.
3. Observe and record the change.
4. On the data sheet, write whether this is a physical or chemical change.
Experiment E: Milk and vinegar
1. Using the graduated cylinder, measure 25 mL of milk and add it to the cup saved from experiment.
2. Using the graduated cylinder, measure 30 mL of vinegar and add it to the same cup.
3. Observe and record the changes.
4. On the data sheet, write whether this is a physical or chemical change.
Experiment F: Kool-Aid and water
1. Add 1 teaspoon of Kool-Aid powder to a small jar.
2. Using the graduated cylinder, add 60 mL of water to the same jar.
3. Close the lid of the jar and gently mix by swirling it.
4. Observe and record the change.
5. On the datasheet, write whether this is a physical or chemical change.
Group Names______
Martian Fuel Station Data Sheet
Experiment / Originalsubstance(s) / Describe
the item
BEFORE
the change / What was observed
DURING
the change?
(Evidence) / Describe
the item
AFTER
the change
(Evidence) / Is it a
physical
or chemical
change?
A-1 / Antacid
Tablet
A-2 / Broken Antacid tablet
B-1 / Ice
B-2 / Play-doh broken into pieces
C / Baking soda
& lemon juice
D / Baking soda
& vinegar
E / Milk &
Vinegar
F / Kool-Aid &
Water
Explain/Evaluate
The following questions should be answered by the students.
1. In which of the experiments were new substances formed?
______
______
2. How were you able to tell the difference between physical and chemical changes?
______
3. It be confusing to recognize the difference between physical and chemical changes.
Give two examples.
______
4. Does the mass of the ingredients change during physical changes? What about
during chemical changes?
______
______
5. In one of today’s experiments, you made a mixture where the ingredients kept their
physical properties. Which experiment was it?
______
______
6. If you wanted to learn more about all the physical changes possible for water, what three
states of matter would you study?
______
Evidence - What is the proof?
(Go back to data table and give three examples of evidence of chemical changes.)
______
______
Reactions cause chemical changes and are accompanied by the following clues:
Gas production: antacid + water; baking soda + vinegar; lemon juice + baking soda
Precipitate formation: milk + vinegar
Heat production: baking soda + vinegar
Sometimes color change is an indicator of chemical change. Ask students where they observed color change in today’s lab? (Kool-Aid was mixed with water.)
Pass around a cup of dry Kool-Aid powder so they can observe the subtle color of the dry powder. The students may argue that a new substance (Kool-Aid drink) was made, but point out that the Kool-Aid powder dissolved or spread out evenly among water molecules. No new molecules were created. Ask students to draw a model of a cup with the water molecules and the Kool-Aid’s molecules fitting in between the water molecules on the board. Discuss how they could exist as separate substances in a special mixture called a solution. (Solutions are groups of molecules that are mixed up in a completely even distribution.) Ask how the Kool-Aid could be separated from the mixture. (Let the water evaporate.)
Evaluate:
The questions at the end of the data sheet can be used to test student comprehension. This lesson requires students to synthesize prior knowledge about states of matter, solutions, and mixtures to understand chemical and physical properties & change. Therefore, any deficiencies in comprehension are likely to become apparent during discussions and/or in answers to the worksheet questions. To test whether students have a full understanding of the subject, present them with some additional scenarios and ask them whether a physical or chemical change occurred.
A few examples:
Cutting paper (physical)
Burning paper (chemical)
Rusting of metal (chemical)
Sugar dissolving in water (physical)
Blowing soap bubbles (physical)
Experiment Station Procedures:Experiment A-1: Antacid tablet
1. Observe and describe the antacid tablet at your table.
2. Break the tablet into small pieces. Is this a physical or chemical change?
Experiment A-2: Broken Antacid pieces
3. Using a graduated cylinder, measure 50 mL of water and add it to a cup. Drop the tablet pieces into the cup.
4. Observe what happens and write whether it is a physical or chemical change on theobservation form.
Experiment Station Procedures:
Experiment B-1: Ice
1. In the empty clean cup, place 1 ice cube. Observe and record how the ice looks and feels.
2. Set the cup and ice cube aside until you are finished with the B-2 experiments.
Experiment B-2: Play-doh
1. Remove the Play-dohfrom its container and describe how it looks, feels, and smells.
2. Break the Play-doh up into many small pieces.
3. Observe and record the change.
4. On the data sheet, write whether this is a physical or chemical change.
Go back to Experiment B-1: Ice
1. Look at the cup that held the ice cube from experiment B-1.
2. Observe and record the change.
3. On the data sheet, write whether this is a physical or chemical change.
Experiment Station Procedures:
Experiment C: Baking soda and lemon juice
1. With a graduated cylinder, measure 40 mL of lemon juice and add it to the small jar.
2. Add 1 teaspoon of baking soda to the jar.
3. Observe and record the changes.
4. On the data sheet, write whether this is a physical or chemical change.
Experiment Station Procedures:
Experiment D: Baking soda and vinegar1. Add 1 teaspoon of baking soda to the cup.
2. Using the graduated cylinder, measure 10 mL of vinegar and add it to the same cup.
3. Observe and record the change.
4. On the data sheet, write whether this is a physical or chemical change.
Experiment Station Procedures:
Experiment E: Milk and vinegar1. Using the graduated cylinder, measure 25 mL of milk and add it to the cup.
2. Using the graduated cylinder, measure 30 mL of vinegar and add it to the same cup.
3. Observe and record the changes.
4. On the data sheet, write whether this is a physical or chemical change.
Experiment Station Procedures:
Experiment F: Kool-Aid and water1. Add 1 teaspoon of Kool-Aid powder to a small jar.
2. Using the graduated cylinder, add 60 mL of water to the same jar.
3. Close the lid of the jar and gently mix by swirling it.
4. Observe and record the change.
5. On the datasheet, write whether this is a physical or chemical change.