Ask yourself: What is it that I want to teach my students? What lessons do I want students to take away? What level of risk is associated with this laboratory exercise? Is the purpose to impress or excite students with color changes, or is it to teach students how to connect observations made at the macroscopic level to what is happening at the molecular level as an equilibrium system responds to stressors? I think it is always important to question the purpose of the learning activity or experiment. Summary of traditional equilibrium systems, color changes, and safety warnings.
#Cobalt chloride le chatelier lab skin
The equilibrium system of cobalt chloride is violet, and students observe color shifts from blue to pink as they add silver nitrate, concentrated hydrochloric acid, calcium chloride, water, and heat/cool the solution.Ĭobalt chloride solution is a flammable liquid and moderately toxic by ingestion.Ĭoncentrated (6M) hydrochloric acid solution is toxic by ingestion and inhalation and is corrosive to skin and eyes.įigure 1. Potassium thiocyanate is toxic by ingestion and emits a toxic gas if strongly heated. Iron (III) nitrate solution may be a skin and body tissue irritant. These systems (detailed in Figure 1) are traditionally studied as part of an investigation of Le Châtelier’s Principle.įe 3+ (aq) is yellow, SCN - (aq) is colorless, and FeSCN 2+ (aq) is red-orange.Īdd iron (III) nitrate and potassium thiocyanate and heat/cool the solution.
There are many different systems that illustrate this effect, including iron (III) thiocyanate and cobalt chloride complex, among others. The qualitative observations of the color changes allow students to predict and interpret various shifts in equilibrium systems as the rates of the forward and reverse reactions change until equilibrium is reestablished. Le Châtelier’s Principle is a favorite topic of my students because of the dramatic colors involved in the reactions. Traditional Le Châtelier’s Principle experiments The first green replacement lab that I implemented in my classroom was Beyond Benign's Equilibrium/Le Chatelier’s Principle lab. These greener replacement labs teach the same skills and address the same standards as traditional experiments, but utilize methods and chemicals that don’t expose our students to unnecessary risk, and are safer for the environment. Green chemistry’s approach to reducing risk - through the elimination of hazards and toxic chemicals - is more effective than trying to lower exposure through the use of PPE.Ĭlassroom and laboratory safety can be improved by reducing the use of hazardous materials by replacing traditional chemistry labs with greener alternatives. Risk, or the probability of a harmful event, is a function of both exposure and hazard, and green chemistry plays a role in improving laboratory safety by addressing the hazard component of the function. However, accidents and unintended outcomes can still happen in the laboratory, especially with inexperienced high school chemistry students. Protocols, procedures, and rules are implemented to make sure the laboratory is a safe place to learn and to reduce the incidence and severity of accidents. Traditionally, this involves reducing the exposure to hazardous substances by showing students how to correctly use safety equipment and ensuring the use of proper personal protective equipment (PPE). Experiments are an essential component of the chemistry curriculum, and as a chemistry teacher it is my job to make the laboratory a safe learning environment.
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