Matter and Change: Physical and Chemical Changes

There are two basic types of “stuff” in the world that you experience every day – matter and non-matter. Matter is often grouped by its properties, and these properties come in two categories: physical and chemical properties. This experiment is actually a series of mini-experiments that will examine several physical and chemical properties of matter. Additionally, these mini-experiments will help students understand and identify both the physical and chemical changes that matter can undergo. Taken together, these experiments represent a complete lesson on the topic of chemical and physical change.

---

1. Hotplates can burn –students should be careful not to touch them when on.

2. Boiling NaOH is caustic – don’t let students near it. Dispose of NaOH by neutralizing and putting it down the drain. Zn is fine to go down the drain as well.

3. Be careful not to let isopropyl alcohol reach its flash point. If this does happen, simply cover the beaker and the flames should die.

4. Do not let students come into contact with steam over boiling water.

---

I. Intro Experiment: Changing a Penny: Copper, Silver, and Gold

• Pre-1982 pennies (at least 3 per class, so that you end up with one of each color)
• Vinegar and steel wool
• 200 mL of 6 M NaOH
• 25 g Zn powder
• Beaker for NaOH and Zn
• Hotplate
• Bunsen burner (if available)
• Tongs

• 200 mL 6M acid for disposal purposes

NOTE: Before coming in, pennies must be cleaned. Soak them in white vinegar overnight and scrub clean with steel wool. You should be left with a shiny copper penny.

II. Interactive experiments

Experiment 1: Making observations

Part 1 (~5 minutes)

• A variety (~20-25) of small objects with differing properties (hard, soft, metal, rubber, cloth, clear, colored, etc. etc.) that can be distributed throughout the group. These should be prepared by attaching numbers to them with tape so that students can identify the objects by number.

Part 2 (~5 minutes)

• 3 empty coffee cans

• a variety of objects.

Experiment 2: Physical properties (~10 minutes)

• Hotplate
• 100 mL beakers
• Several liquids (with different melting points, for example water = 100°C, isopropyl alcohol=83°C)

• thermometer

Experiment 3: Physical change
Part 1 (~2-3 minutes)

• A package of graham crackers, with the perforations

Part 2 (~10 minutes)

• A sheet of cold metal
• boiling water
• room temperature water

• two ice cubes

Experiment 4: Chemical change (10-15 min)

• Liquid iodine (diluted in water to ~ 3 parts water to one of iodine solution)
• Alcohol (~10 mL isopropyl is fine)
• Starch/water solution (just a small amount of cornstarch dissolved in ~10 mL water)
• Yeast (must be live, active)
• Water (warm, but not hat. Maybe 50-70°C)
• Milk
• Vinegar (white is best to avoid any color change)
• Sugar
• Hotplate

• Several small beakers for the experiments.

---

Set-up:

It takes a while for the water to boil, so you may want to start that ahead of time. For the introductory demo all the solutions should be prepared ahead of time.

I. Intro Demonstration: Changing a Penny: Copper, Silver, and Gold
Part 1: Turning Copper into “Silver”

1. Mix the zinc into the NaOH in a beaker. Place this beaker onto a hotplate to heat and stir.
2. Using tongs, carefully place two pennies into the solution once it is boiling. Occasionally agitate the pennies in the solution. They should become “silver,” usually in less than a minute.
3. Remove pennies from the boiling solution and rinse with water.

1. Hold up an original penny and the “silver” penny for the students to observe.

Part 2: Changing “Silver” into “Gold”

1. Gently heat one “silver” penny on the hot plate (or with a Bunsen burner if available – use a blue flame) until it becomes golden in color.
2. Remove the penny and quickly dip it into the beaker of cold water.

1. Hold up an original penny, a “silver” penny, and this final gold penny for the students to observe.

II. Interactive Experiments

Experiment 1: Making observations
Part 1 (~5 minutes):

1. Have each person create a table of ~5 objects, listed by number, and describe each as fully as possible WITHOUT using the object’s name or purpose as part of the description (i.e. saying flat, shiny silver circle with raised portions and a rough edge for “quarter”). Have the kids do this quietly, on their own, for at least some of the objects after perhaps doing one as a group to get them started.

1. Have one person read a description of an item that they wrote to the group. The group should then try to guess which item is being described. Go around the circle of students, having each read a description for a different object Keep track of how many correct description/object pairs the students make.

Part 2 (~5 minutes):

1. Put several (3-6) objects that have at least one quality in common in each can before your group arrives for the day (some suggestions include having one of fairly soft objects, one of hard, one with objects bigger than everything else, etc.).
2. Have the students empty the items from one can onto the table and attempt to find what physical properties each of the objects share. Again, initially do this quietly. Repeat for each can.

1. Have students discuss their classifications: did everyone use the same physical property to describe the objects in each can?

Experiment 2: Physical properties (~10 minutes)

1. Fill several small beakers with ~50 mL of liquid, at least two of which are water.

1. Heat each liquid to boiling, and have the students CAREFULLY measure the temperature of the boiling liquid. It should be different between the water and other liquid, but two samples should be the same.

Experiment 3: Physical change
Part 1 (~2-3 minutes): Easily recognizable physical change – graham crackers

1. Take a graham cracker out of the box and ask the student to describe its properties and write them down.
2. Break the graham cracker along one of the perforations.
3. Again ask the students to describe its properties, noting anything that has changed on their worksheet.

1. Break the cracker again, and again have them note what’s changed.

Part 2 (~10 minutes):More esoteric physical change – water
NOTE: there is a strong possibility of a steam burn with this experiment. DO NOT have a student actually do this experiment. This should be a demo carefully performed by an adult helper.

1. Ask students to make observations (aloud or in writing) about the water and its state of matter. Explain that boiling is the process of turning liquid water into a gas, and melting is the process of turning a solid into a liquid. You’ll make observations about both of these changes.
2. Hold the cold metal plate over the beaker of boiling water, being careful not to expose yourself to the steam directly. Some water should condense on the plate. You can then turn the plate over and have students make observations about the condensed water.
3. If an un-melted ice cube is available, allow it to start melting on the table while you are doing the above, and ask students to explain any changes they see in the ice cube. When you’re done with the vapour part of the experiment, take out a second ice cube (unmelted) and ask the students to make observations about the two cubes (one should be frozen, one partially melted).

1. Ask students to make observations about the liquid on the metal plate, each ice cube, the boiling water in the beaker, and a beaker of tap water.

Experiment 4: Chemical change (10-15 min)
Allow the students to mix several of the above together and see what happens

1. one or two drops iodine solution into a couple of mLs of alcohol in a cup. (should change from yellow/red to brown)
2. one or two drops iodine solution into a couple of mLs of starch solution in a cup. (should change from yellow/red to blue when stirred)
3. add yeast to water (should form carbon dioxide. Should also evolve a noticeable odor even if you don’t produce enough CO2 to see)
4. heat a small amount of sugar in a beaker on the hotplate (should melt/caramelize)

1. add a splash of vinegar to milk (milk should separate and start to curdle)

---

Discussion Points

1. Physical properties can generally be observed and/or measured and include size, shape, color, density, mass, boiling point, melting point and phase (state) of matter.
2. Chemical properties involve the ability of one material to turn into another material. These properties can be much harder to observe without sophisticated experiments
3. We can change the properties of matter. Since there are two types of properties, there are two types of changes: physical and chemical changes. Physical changes do not change the material; chemical changes do change the material.

1. Often, a chemical change is accompanied by a change in one or more physical properties: for example a color change, or a change of state.

Follow-up Questions for Experiment 1: Making Observations

Q: What types of properties can you easily observe?

A: State of matter, color, hardness, density, odor, size, and shape.

Q: Which of the properties that you used to describe these objects are actually because of what the item is made of? Which are not?

A: A variety of answers are possible – for things like metals, color is a true physical property. Shape is not (i.e. not all silver is in coins), but state of matter is. Lead the discussion as appropriate for the actual descriptions given by students.

Q: Are there other ways that we might have grouped these materials?

A: Again, a variety of answers are possible – just guide the discussion, making sure that the students seem to understand the concept.

Follow-up experiment: have the students put the objects into one of the new categories – bonus if they can take one object from each can and have them go together based on a different property.

Follow-up Questions for Experiment 2: Physical properties (~10 minutes)

Q: What can you say about the chemical nature of the three liquids?

A: One is obviously different from the other two.

Q: How is this like the previous experiment?

A: You can use the temperature (boiling point) as a way of grouping the two water samples together..

Q: Is boiling point a physical property?

A: Yes.

Follow-up Questions for Experiment 3: Physical change

Q: Did anything change when we break the cracker?

A: Yes – size.

Q: Does this change in size also change the material?

A: No – still a graham cracker.

Q: What type of change is this, physical or chemical?

A: Physical.

Q: How are the water in the beaker and the water on the plate related?

A: It’s the same material chemically – you’ve simply forced it to undergo two physical changes (vaporization and condensation).

Q: What differences do you see in the water after it’s been condensed versus when it’s boiling in the beaker? Between boiling water and tap water? Tap water and ice cubes?

A: Most obvious answer is temperature. Shape will also be mentioned when using the ice cubes as a point of comparison.

Follow-up Questions for Experiment 4: Chemical change

Q: What kinds of changes did you see in the experiment?

A: Various answers: change in color, texture, smell, etc.

Q: How do you know that these are chemical changes?

A: For the most part, they can’t be reversed – you can’t uncurdle milk, for instance, or uncarmelize sugar, or put the CO2 back into the yeast. This is because a chemical change has occurred that means the material is now longer what it started out as.

---

There are two basic types of “stuff” in the world that you experience every day – matter (most of what you experience) and non-matter (thoughts, sound, etc).

Since so much of what we experience is matter, scientists often try to group different types of things together somehow. Matter is often grouped by its properties, and these properties come in two categories: physical and chemical properties. Physical properties can generally be observed and/or measured and include size, shape, color, density, mass, boiling point, melting point and phase (state) of matter. Chemical properties involve the ability of one material to turn into another material. These properties can be much harder to observe without sophisticated experiments. For example, electricity can be used to break water into hydrogen and oxygen, so the ability to be broken up by electricity is a chemical property of water. Similarly, it is a chemical property of alkali metals that they can react with halogens to form salts. We can change the properties of matter. Since there are two types of properties, there are two types of changes: physical and chemical changes. Physical changes do not change the material; it remains the same stuff after the change. Chemical changes do change the material, and are often irreversible, and are often accompanied by a change in one or more physical properties: for example a color change, or a change of state

---

1. Dispose of NaOH by neutralizing and putting it down the drain. Zn is fine to go down the drain as well.

---

---

A really nice — and fun — finish to this series of experiments would be the luminol demonstration. Following this demo, students can discuss the chemical changes of the first and final demos.

---