Chemistry Solutions

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Each week, I begin my first-year chemistry classes with a demonstration, which is now known among students at our school as “Magic Monday.” I attempt to choose demonstrations that relate to the particular content that we are covering or a science practice I wish to encourage — and either choice is sure to excite students and get them thinking. With more emphasis on inquiry and engineering practices in science education, I believe that demonstrations are a great way to begin that process.

Demonstrations allow students to gather evidence to construct explanations of phenomena or discrepant events in science. They also require students to apply their knowledge of scientific principles and promote discussion among peers, and teach students how to defend ideas in science. My goal of using demonstrations in chemistry is not only to excite students, but also to encourage them to think about scientific concepts and acquire observations skills that allow them to question what they observe.

Getting started

I know what some of you may be thinking: “I don’t have the time to add in demonstrations and still cover material.” Yes, it takes time to plan, gather materials, practice, and perform the demonstration … but the outcome is worth the time and effort you put in! And, the students absolutely love them. The first thing my students ask upon entering class on Monday is, “Do we have Magic Monday today?” There are a few resources that I use to make the planning simple:

• A Demo a Day — A Year of Chemical Reactions, by Gross, Bilash & Koob
• Chemical Demonstrations: A Handbook for Teachers of Chemistry, by Shakhashiri

Additionally there are many chemistry demonstrations available on the AACT website. Some that are both simple to do and helpful for understanding include:

• Exploring Gases (for teaching gas laws)
• Giant Toothpaste (for teaching exothermic reactions)
• Milk of Magnesia Magic (for teaching acids and bases)

Essential practices

We have all heard that practice makes perfect … and nothing could be truer regarding chemical demonstrations. Be certain to practice all demonstrations several times before performing them in front of students. This practice allows you to make certain you understand the safety parameters required and the chemistry that drives the reactions, and at the same time, become better prepared to answer student questions. It is incredibly disappointing to the students when a demonstration does not work because it has not been properly practiced.

Safety in the lab

Safety first should be your mantra, as it is paramount to keeping our students safe. Make certain that you are aware of any hazards for the materials you plan to use in order to avoid unnecessary risks (such as methanol near flame), and remember that there are usually safer alternatives. If you are not confident or familiar with a material, reach out to an experienced colleague or college chemistry professor to get help. Additionally, use a fume hood or safety shield when performing demonstrations, and make sure to wear goggles and a lab apron or coat — and always require students to take the same precautions while observing demonstrations.

It is important to prepare only the minimum amounts of chemicals required to perform the necessary trials, and be sure to read the Safety Data Sheet (SDS) for each chemical that will be used. All chemical disposal should follow local disposal requirements. A couple of great safety resources are:

• ACS Guidelines for Chemical Laboratory Safety in Secondary Schools
• Flinn Science Catalog and Reference Manual (free upon request)

Creating the magic

The beauty of using demonstrations is that you are free to be as dramatic as you like when you present them to students. To get the most out of the inquiry process, I recommend that you give away very little information as you perform the demonstration.

As the demonstration proceeds, I usually ask students to make observations. To help them, I provide an observation sheet (see Figure 1) to encourage students to think scientifically. Typically, I only use this during the first few weeks of school until students develop the skills to record their own observations without depending on the handout. Once complete, we then discuss the findings as a class.

The first time we use the sheet, the students typically have difficulty completing some of the sections, especially where they are asked to determine reasons for the changes they observe. As the year progresses, I add questions to the discussion such as: Was the reaction exothermic or endothermic? Was a catalyst used? Was the activation energy large or small?

Figure 1. Student worksheet used to record observations during demonstrations. Students complete only the sections relevant to the particular demonstration.

You can choose a demonstration to help students understand a particular topic, or to simply get them thinking about a chemistry concept. My demonstration on the first day of school is the dehydration of sugar with concentrated sulfuric acid, as shown in this video. This demo is a favorite among students, as they do not expect the outcome that follows. The reaction takes a few minutes to really “take off,” teaching students the importance of patience while making observations in science.

I choose to use this as my very first demonstration because most students come to chemistry class after completing biology, where they have learned about sugars; as a result, most recall that sugar is made from carbon, hydrogen, and oxygen. This is advantageous, because most students understand that the black substance left at the end of the reaction is carbon. I allow students to take turns at the fume hood and use a glass stirring rod to test out the texture of the carbon product. We further discuss the dehydrating effect of sulfuric acid, and what effect that might have for skin, respiratory tract, and eyes — all of which makes for an excellent safety discussion.

Another example demonstration I use when we study periodic properties is to show students the reactions of alkali metals with water. I cut small (pea-sized) pieces of lithium, sodium, and potassium to use, but leave them in oil prior to the demonstration. I begin by placing a small piece of lithium in a 400-mL beaker half-full of water; I then proceed to sodium and potassium.

As I advance through the metals, I guide the students to think about what they know about the alkali metals and their periodic properties including size, number of electron levels, and number of valence electrons. I ask the students to propose a reason for what they have seen, and to explain the difference in the reactivity of each metal. I also ask them why they think the metals are stored in oil, and to suggest what would happen if the remaining alkali metals were also available to demonstrate. Then I show them the video, “Braniac Alkali Metals,” available on YouTube. They are always amazed at the reactivity of these additional metals.

Students love demonstrations that involve spontaneous exothermic reactions. One of the favorites in my classroom is the oxidation of glycerol with potassium permanganate, known as the Potassium Permanganate Volcano (there is another similar version available in the AACT Classroom Resource Library). This demonstration of the oxidation of glycerin (glycerol), using potassium permanganate as a catalyst, gives off a tremendous amount of gas, heat, and a purple flame. The students always ask for a repeat of this demonstration. It is an excellent way to discuss endothermic and exothermic reactions, oxidation and reduction, the use of catalysts and, depending on the level of the class, the topic of spontaneous reactions.

The only information I provide to the students is to tell them which chemicals are used in the reaction — and then I begin. During the demonstration, I ask students some guiding questions to help them consider what they might be observing, such as:

• What type of compound is potassium permanganate? Typical response: ionic.
• What type of compound is glycerol? Typical response: an alcohol.
• Why are there flames? Typical response: the temperature is so hot that the gases ignite.
• Why does the flame look purple/violet? Typical response: potassium burns purple.
• Is the reaction endothermic or exothermic? Typical response: definitely exothermic.

Students complete the observation worksheet as they watch the reaction. Sample student observations are supplied in Figure 2. After the demonstration, I provide some insights into their observations by providing the chemical equation for the reaction that they witnessed. This leads us into a discussion where we identify which species in the reaction is oxidized and which is reduced, and also determining whether the reaction was endothermic or exothermic. A full sample post-demonstration discussion can be found in the demonstration resource, available for download.

Figure 2. Student worksheet about the Potassium Permanganate Volcano demonstration (sample answers in red).

Demonstrations offer a low-stakes opportunity for students to ask questions, formulate predictions, and make mistakes. Chemistry is a difficult course for most students, and especially first-year students. Concepts can be hard for students to visualize, and a demonstration may be just the thing that turns on the proverbial light bulb.

For these reasons, I believe it is important to take the time to show science in action, and invite students to participate in demonstrations where applicable. In my experience, students are always excited about demonstrations and continue to ask for them each week. The more often you present demonstrations in your classes, the more comfortable you will become with your students, and the more comfortable they become with one another. The student engagement that demonstrations create certainly makes the effort worth the effort.

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