A Guided Introduction to Experimental Design and Optimization

For students not used to creating their own protocols, the process of guiding them to do so can be arduous. Many students are used to being given a list of steps to follow, and the slightest deviations from the classroom norms are met with tremendous amounts of hesitation. After all, the act of composing a list of steps does not come naturally to many students but can be gradually introduced. At Acera, we frown on those “cookbook” style labs and seek to introduce the skills of invention and scientific inquiry into our lab projects. The introduction of those tactics to some students, however, is incredibly challenging, so the goal of our November experiment was to teach the basics of experimental design by having students alter the ratio of 2 chemicals to see how it changed the overall chemical reaction.

 

Potassium Nitrate, or “salt peter”, is a well known oxidizer or donor of electrons. When it encounters a reducer, such as dextrose or sucrose, and a flame, it produces lots of non-toxic smoke. Increasing the sugar slows the reaction to the point at which only a trickle of smoke that lasts up to an hour emerges. On the contrary, changing the nitrate concentration increases the rate of reaction and the smoke output. I asked students to design an experiment to test which ratio of potassium nitrate and dextrose produces the most smoke. The experimental process is simple: Combine a 5 part ratio of nitrate:dextrose with 1% sodium bicarbonate in a 600 mL tempered glass beaker and heat while stirring with a strong wooden stick at 250-300C for 15-30 minutes until the sugar is melted, dark brown, and paste-like in consistency. The resulting mixture is then scraped onto aluminum foil and allowed to cool. Finally, it is brought outside and the teacher can safely light the dried paste on a metal baking sheet while the students watch from a minimum of 5 meters back.


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It is important to note that this is a very strong reaction, and there are many safety considerations. We mandate that students wear lab coats, a face shield or goggles, and two pairs of gloves during the heating. Also, when the time comes, the students must not light the reactions. The ignition and resulting smoke can emerge very quickly. It is also recommended that the teacher practice and demo this lab extensively in advance to gain familiarity with the overall process.


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So, the question is, why perform such an extreme reaction when more mild ones can be substituted? After all, there are pretty easy ways for students to work with chemical ratios, including baking soda and vinegar. Simply put, the students want to work with something that is a little bit more reactive and will naturally pay closer attention when they are working with something that they perceive is “dangerous.”

 

Obviously, safety is a top priority, and our students have undergone extensive safety training that was detailed in a prior blog entry. The training was to prepare students for adverse events that may happen when working with chemicals that are beyond the norms of traditional school science. Having this lab tech training means that they can do things that are a little bit out of the realm of normal. A more dramatic reaction will really help them to understand the nature of the chemicals, the energy transfers involved, redox reactions, and the importance of experimental ratios in guiding research. Finally, the students will think it’s cool!

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This is an important point, and once they start seeing the different reactions, they will attempt to optimize their ratios and experimental design to create even more smoke producing reactions. The streamlining of protocols is a very important skill for scientists to have and can be used for all future experiments. For the teacher, it is also crucial to remind students to keep a running log of their results and adaptions to their protocols. After all, the purpose of this lab is to optimize an experimental ratio and work on lab report writing skills.

 

Another facet of this experiment is allowing students to collect their own lab results. They know that they need to find the reaction that produces the most smoke, but the students are able to come up with different means of getting that information. Some measured duration, others took pictures and isolated the smoke hue, while still others measured the meters away from the reaction in which the smoke plume was visible. No matter what method the students used, they all collected a set of data points that they could use to compare the different ratios.

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Once the students had completed the ratios or exhausted their lab time, the conclusion was completed and a number of different topics were addressed. I started the post lab by asking the students what things the conclusion should contain. They mentioned discussing which reaction was the strongest and why, on a chemical basis, the reaction behaved the way it did. The student reactions were varied. They responded with a variety of tie ins to chemistry including energy generation, the science of redox reactions, and predicting reaction products between the nitrate, dextrose, and sodium bicarbonate.

 

From here, there are a number of jumping off points for future discussions including redox reactions, energy, and even the environmental effects of CO2/CO. As for the lessons taught in this lab, experimental design is something that can be worked on and perfected throughout the year. The more the students get exposure to true inquiry, the easier it will get. Like all skills, it needs to be reinforced and practiced to become second nature.

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Teaching Energy as a Concept

Throughout this year, the underlying theme for all our experiments was chemical reactions and the importance of energy. Generally, in a traditional chemistry classroom, there are five basic types of reactions that are discussed and tangentially performed: single replacement, double replacement, combustion, synthesis and decomposition. In most curricula, the importance is placed on the names and details regarding the reactions without emphasis on the underlying reasons for why the reactions proceed. In essence, chemistry is the study of transformations and energy is a tremendous guiding force in ensuring reactions occur spontaneously yet energy is usually not discussed in this unit.

A simplistic view of a calorimeter

Calorimetry studies the energy generated in chemical reactions but is usually only reserved for AP Chemistry classes yet the general ideas behind this concept can be taught to virtually any age. In short, it is the study of energy in the form of heat. The process for conducting a calorimetry experiment is very simple: when a known amount of chemical is added to a known amount of water, the chemical may ionize (“come apart”) depending on its bonding and release energy into the water changing the heat of the solution. This change in temperature is directly proportional to the heat produced by the reaction of the added chemicals with water. To measure the energy produced, students can build a simple apparatus called a calorimeter using a beaker, test tube, or even a styrofoam cup, a lid or cap, and a lab thermometer though far more complex designs are possible. For an added math element, the students can actually calculate the heat in Joules produced by multiplying the change in temperature of the water (in Celsius), the mass of the water plus added chemical, and the specific heat capacity, which is a constant. For an added lesson in metric system skills, the students can convert the heat in joules to kilojoules (kJ), a more common unit in the reporting of energy or to kilocalories for a real world link to foods and energy. In addition, as either an introduction or extension activity, students can actually experimentally determine the specific heat capacity of water which is 4.18 Joules / (grams * Celsius).

The formula for the calculation of heat generated in reaction

In the Acera lab, we spent several weeks on this project. First, the students were given a class period of two hours to design and troubleshoot a calorimeter with common items they found in the lab or school. Some of the problems that the students faced in their calorimeter design was water leakage, how to add the chemical in an effective manner, and the biggest problem of how to avoid heat loss to the surrounding environment. Finally, given the tremendous amount of choice regarding size of hardware and limitation of reaction materials, the students need to be cognizant of choosing the best equipment for the job and for the reaction materials required. In order to begin, the students needed a cogent design but adapted the design if a problem arose as troubleshooting is a routine part of every experiment.

Several examples of calorimeters

Several examples of calorimeters

Once they feel they have a final optimized design, I gave them a variety of chemicals in which to experiment. This included ammonium nitrate, which endothermically reacts with water and lowers the temperature of the liquid. I also gave them dextrose, which does not ionize in water due to its bonding and thus, does not modulate the temperature. I also included the exothermically reacting chemicals lithium chloride, sodium chloride, hydrochloric acid, and sodium hydroxide. Finally, with my assistance, the students also reacted very small amounts (0.1 – 0.3 grams) of elemental sodium and lithium under a chemical extraction arm (or hood) to collect the gases.

Students performing calorimetry experiments

Students performing calorimetry experiments

Safety note: It is advised not to let the students react the elemental sodium and lithium unsupervised as they react with water very strongly. In addition, the sodium must be sliced very thin as spherical pieces can result in flash of light and a loud popping noise. While harmless, the reaction can be very startling. You could leave these out entirely but the very rapid reaction of these reactions can provide a lot of insight into the nature of the first column of the period table.

Lab notebook schematic of a calorimeter

Lab notebook schematic of a calorimeter

Once the the students have gathered all their data from the various experiments, the real scientific learning begun as they researched the chemicals to determine why they behaved the way they did. In our class, the concepts that this analysis touched upon was reaction types, ionic vs. covalent chemical bonding, energy creation from broken chemical bonds, and of course the nature of chemical reactions. By performing these experiments, they understood the ideas behind ionization and rearrangement of the atoms in the compound which included different reaction types. It is true that the upfront vocabulary behind the experiments was minimized but the #1 most common complaint I received as a teacher is that science education has too much complicated vocabulary. In this experiment, the students organically came by the various vocabulary with research which is similar to real life lab environments.

Lab notebook results page

Lab notebook results page

The only rules I have regarding the experimental analysis is that the students are done writing when they are no longer able to write original thoughts that they understand. This means that the students cannot repeat themselves and they also cannot copy down words or concepts that they can’t explain in their own words. Whenever students aren’t given some guidelines, there is the danger that they will begin copying down passages from textbooks that they don’t understand which is not productive by any means.

Cumulative results on the whiteboard

Cumulative results on the whiteboard

The more advanced students delved into the electron configurations of ionic vs. covalent bonds while some examined the physical chemistry of reactions and the students scientific mastery simply discussed the basics of endothermic and exothermic reactions and the links to the chemicals they worked with. As the students were writing their conclusions, I offered feedback and helped guide them away from quagmires. All students should however, discuss and suggest the reasons for the differences in energy and namely, why the addition of a chlorine ion to sodium and lithium lowers the heat generated in solution. Finally, when we performed this lab, I asked the students to write their results on the whiteboard so that they can compare their results to that of other students and to potentially discuss it in their lab notebooks.

Lab notebook results page

Lab notebook results page

In conclusion, this unit provided a view on the nature of energy and chemical reactions. From here, we moved into the optimization of chemical ratios in producing a more energetic reaction which I will discuss in my next blog. However, additional jumping off points can be an analysis of the individual reactions, food calorimetry, or even enzymes and energy in organic materials.

Reimagining Lab Safety

The beginning of every year in a school lab traditionally consists of a didactic read aloud from a handout on lab safety. Sure, the teacher can pepper the language with a bit of levity but in the end, it’s still a set of rules that students will memorize long enough to pass the requisite safety quiz to get into the lab. The teachers and students know of the importance but this doesn’t stop the fact that it is viewed as an impetus in getting to the lab and doing experiments. At Acera, we removed the teacher led aspects of the safety aspect to give the students more ownership of the rules of the lab. After all, they will be the ones using it and they are the ones that are the most unfamiliar with the ways of laboratory research. This made the process significantly more interesting, entertaining, and useful in giving students a groundwork in lab safety.

Our first day of training consisted of the development of a set of lab norms. To do this, the teacher simply asked what rules should be followed while in lab that are not standard for the classroom. Sample dialogue included:

Teacher: What is a good rule to have in lab?
Student: Don’t eat lab chemicals!
Teacher: Why is that a good one?
Student: Because they could be dangerous.

Given that most every student will ask about putting lab chemicals in their mouth, the students must obviously know why they can’t eat potentially hazardous chemicals. It is also important to ask the students why a certain rule is in place so that the consequences are clear.

After the rules discussion, we performed an interactive safety demonstration. With guidance from the teacher, the students acted out what to do in case of chemical fires, fire blanket, chemical burns on skin, eye wash and emergency shower use (which included activating both of those), spills, glove removal, the NFPA diamond and proper chemical handling, and appropriate personal protective equipment (PPE). By bringing in the student to demonstrate, they get to touch and use the equipment but in a non-emergency manner. This helps them to use their bodies to perform the actions and gain familiarity with the motions required to use the equipment.

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Given that ours is a K-8 school, we have a school set of safety levels for experiments that go from 1 (least hazardous) to 5 (most hazardous). Experiments at each stage have different safety considerations and students should show respect and maintain safety for everything we do even if it simply involves kitchen chemicals. After establishing the lab norms and all the safety practices, the students were then tasked with making a creative project on the safety levels and the considerations of each level. Some students made posters, puppet shows, and skits, both filmed and animated. This helped to create a more organic feel to the training and enabled them to be creative and to capture these “rules” and adhere them to their own personalities in a simulated lab situation. In addition, since many of these activities demonstrated what not to do, they experienced firsthand through fictional demos the results of veering away from the lab norms.

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Finally, the students took a safety assessment that they all must have scored a 100% on to take part in lab activities. The students will of course allowed retakes until they reach that goal. After achieving the perfect score, the students were then given a duplicate safety contract for both student and guardian to sign.

Feedback from the process has been very positive from the students and despite it being “safety training,” they learned and had fun doing it. They were able to gain a working knowledge of the lab and will be prepared for unexpected events. Ensuring that the students are comfortable and prepared is the first step in enabling some fascinating science in all of unpredictability and move away from the cookbook labs that are standard in K-12 science education.