Chemistry Solutions

As I strive to improve the quality of my teaching, I tend to look for instructional strategies that increase student engagement and promote critical-thinking skills. In classrooms that feature active learning, students are frequently on task and interested in what they are doing. In addition to creating an environment in which students enjoy learning chemistry, this also helps me alleviate common classroom management problems.

Positive relationships

A significant body of research indicates that students are more likely to perform well academically when they feel that their teacher cares about them. In my opinion, this process begins on day one. I have students take photos of each other on the first day. These photos help me learn students’ names quickly. I have students fill out surveys so I can learn about their interests and extra-curricular activities. As I walk around the room, I take note of their interests. For example, I might discover that a student plays a particular sport, enjoys reading, or loves to draw. I can use this information to strike up a conversation about things they care about. Building positive relationships with my students during the first few weeks of school is beneficial to me all year long. Students are more likely to participate if they know that they are valued as important members of the classroom community.

Chemical demonstrations

One technique that works well in my chemistry class is using demonstrations to stimulate students’ curiosity. These demonstrations don’t have to be complicated or elaborate. I use them to grab attention and provide students with an opportunity to ask questions, make predictions, and explain the principles behind what they observe. The following scenario is an example of demonstrations I use to introduce properties of liquids.

First, the students draw the structural formulas of water and hexane and calculate the molar mass of each substance (H₂O = 18 g/mol; C₆H₁₄ = 86 g/mol). Then I have them predict which liquid will have a higher boiling point. No matter which liquid they choose, they need to justify their prediction with some sort of scientific explanation. I have them write down their ideas for a few minutes before turning to a classmate to explain their thinking.

Note: Chemical demonstrations must be performed in a safe manner so as to minimize the risk of injury to students or the teacher. Read more here.

I pour equal volumes of each liquid into two separate beakers (Figure 1). Then I place the beakers on an electric hot plate that has been set to approximately 120 ^oC. The results are dramatic and obvious (Figure 2). Students see that hexane boils quickly and water takes longer to come to a boil. (BP_hexane = 68 ^oC; BP_water = 100 ^oC). Prior to this demonstration, some students might have thought that hexane would have a higher boiling point because of its larger molecular size or mass. Even the students who predicted that water has a higher boiling point may not fully understand the scientific explanation. At this point, all students have a reason to explore this topic further. Some may want to discover why their prediction was wrong. Others may need to clarify the reason why their prediction was right.

Figure 3: Equal volumes of water (left) and hexane (right) are placed on the counter.

Next, I transfer about 2 mL of each liquid onto the laboratory counter. Students can easily see the differences in cohesive forces and evaporation rate between the two liquids. While the volumes are identical, the hexane spreads out quickly into a large circular area, whereas the sample of water covers a much smaller circular area (Figure 3). The hexane evaporates in a short period of time, whereas the sample of water remains visibly unchanged. I provide students with the definition of vapor pressure and then ask them to make a prediction about which liquid will have a higher vapor pressure at room temperature. Most students understand that since hexane evaporates more readily than water, it should have a higher vapor pressure (VP_hexane = 151 mmHg; VP_water = 24 mmHg @ 25 ^oC).

Figure 4: A thin stream of water bends toward a balloon that has a static electric charge.

After these demonstrations, students are ready to discuss the reason why these differences occur. I fill two burets, one with water and the other with hexane. I take a small inflated latex balloon and ask a student (who has long hair) if I can “borrow some electrons.” I ask the student to rub the balloon on his/her head to generate a static electric charge. (This works better on a cool, dry day.) I open the stopcock on the buret to allow a thin stream of water to flow from it. Students observe the stream of water bending toward the charged balloon (Figure 4). However, hexane does not exhibit any attraction toward the balloon.

At this point, the conversation continues about polarity, intermolecular forces, vapor pressure, and boiling point. It is helpful to use a series of simple demonstrations to help students visualize and understand abstract concepts. Students can also make predictions about the behavior of other liquids based on the polarity of the bonds and the overall structural formula of a compound.

Student discussions

As a chemistry teacher, it is easy to get caught up in the routine of lecturing to students. After all, it is safe to say that I know more chemistry than they do. However, part of the process of building relationships with students involves recognizing that they bring their own knowledge to the classroom. I value them not only for who they are as individuals, but also for the information that they have. Even if students have misconceptions, it’s important to build an environment where students are willing to share their ideas with their classmates (and with me). I often try to convey the following message to my students: “Your contribution to this class is valuable. If you have knowledge, share it with others. If you don’t know something, ask your classmates.”

The benefits of an interactive classroom have been demonstrated by professors such as Eric Mazur (Harvard University) and Matthew Stoltzfus (Ohio State University). Although there is a time for teachers to give direct instruction, it is important to recognize the value of what can happen when a teacher says, “Check with your neighbor and see if you can convince them why you are right.” While students are talking to each other, I can walk around the room, listen for misconceptions, and try to find out what the majority of students think. When I gather them back together, we can discuss important relevant chemical principles to ensure all students understand.

Classroom discussions can give each student an opportunity to be heard, which rarely occurs in a teacher-centered environment. Nonetheless, there may be students who are quiet or feel uncomfortable sharing their ideas with others. Formative assessment techniques (see the September issue of Chemistry Solutions) can help me ensure that I hear from every student. Since I have a small classroom (fewer than 30 students), I enjoy using the “low-tech” version of a student response system: index cards. I ask a question and give each student a card on which to write a response. Unlike the use of clickers, where students vote for an answer, I am not restricted to asking only multiple-choice questions. Students can draw a structural formula, perform a calculation, or write an explanation. Each student puts his/her name on the card and gives it to me within a certain period of time. As I flip through the cards, I can share the misconceptions that I find without identifying the names of the students to the entire class. This type of informal assessment can inspire me to ask further questions or serve as a stimulus for student discussion.

A person may decide to become a teacher because of a thirst for knowledge. Teachers know that learning should be fun, and many teachers use a variety of techniques to keep students engaged and interested in the material. When a teacher creates a classroom environment in which students are encouraged to be active learners, it makes the process of teaching and learning so much more enjoyable.

The importance of positive teacher–student relationships

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The importance of an interactive classroom

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