Surfactants
Contextualize
Linear alkyl benzene sulfonate (LAS) is the surfactant most commonly found in laundry detergents. Given the scale to which it is used by society, it impacts the environment through its manufacture and downstream release into the environment by consumers. This product also affects the economy through manufacture and sales, supply and demand. The use of this chemical compound has positive impacts on human health based on its ability to clean surfaces but may also have negative effects due to its capacity to disrupt cell membranes. The manufacturing process can also impact human health directly or via environmental effects; the persistence of this substance in the environment enhances its ecotoxicity. The analysis and discussion of the properties and behavior of this surfactant create rich opportunities to introduce central ideas about structure-property relationships in chemistry and analyze the benefits, costs, and risks of synthetic chemical products.
Focus
The large-scale use of laundry detergents containing the surfactant Linear Alkylbenzene Sulfonate (LAS) has a significant impact on our society, economy, and the environment. The industrial manufacture of LAS from non-renewable feedstocks, the consumption of energy from fossil fuels during its elaboration, and the production of hazardous waste in the search for improved yields and better-performing detergents form part of the economic subsystem. Production costs, supply, demand, and profits influence the economy and society. The use of LAS has helped improve societal health and hygiene but could have harmful health effects at a sub-cytotoxic level. However, inappropriate use and failure within society to maintain wastewater treatment could increase LAS concentrations in the environment and impact aquatic life through ecotoxicity and foaming, reducing water quality and increasing its biodegradation rate. Knowledge of the physical properties of LAS is needed to explain its emergent system behaviors that result in desirable properties for cleaning and undesirable properties such as foaming that slows biodegradation. Given the number, nature, and complexity of the factors involved, this infographic summarizes key areas of focus in this lesson:
Define
Central Ideas:
The chemical composition and molecular structure of LAS determines the amphiphilic properties of this surfactant, which in turn are critical for its function as a household detergent.
Intermolecular forces between LAS, water, and oil/dirt molecules lead to the formation of micellar structures that facilitate the removal of unwanted substances but also determine LAS' cytotoxic effects on health.
A variety of organic chemistry reactions are involved in the industrial manufacture of LAS. Multiple factors, such as the nature of raw feedstocks, synthetic techniques, energy consumption, and byproducts need to be considered to obtain high yields and high-performing performance.
Foaming is an emergent behavior resulting from interactions between LAS, air, and water that are affected by diverse environmental conditions and can have serious environmental consequences.
We must understand the conditions required and reactions involved in LAS biodegradation to evaluate and control its ecotoxicity in the environment.
Core Practices
Develop and apply molecular-level reasoning to explain how chemical structure, such as the number of carbons, isomer branching, and chain length, influence energy consumption during fractional distillation, foaming, and ecotoxicity.
Examine and understand molecular-level concepts and processes that influence system-level behavior (intermolecular forces, structure-property relationships, micelle formation, synthesis, and biodegradation reactions)
Move between different levels of granularity to determine how core chemistry concepts can influence physical and chemical properties, emergent behaviors, and subsystems on a larger scale.
Apply concept mapping skills to visualize and evaluate relationships within subsystems and interactions between subsystems to determine cyclic and dynamic behaviors that could aid in making predictions.
Systems Thinking Skills
System Composition: Identify and characterize the chemical and physical properties of the surfactant LAS and its role in society, economy, and the environment.
System Structure: Explore and evaluate the relationships between the structure of LAS and solubility of LAS, and its role in hygiene and health in the societal subsystem. Explore and evaluate the relationships between the organic reactions used in industrial manufacture and the resulting feedback loops within the economy.
System Behavior: Evaluate how the solubility and structural properties of LAS together with environmental variables influence its foaming, biodegradation rate, ecotoxicity, and change in concentration over time.
System Effects: Make decisions based on predictions about the risks and benefits of LAS within and between the societal, environmental, and economic subsystems.
Socio-Environmental Competencies
Consider the role of human activities on current and future system-level behavior associated with LAS and laundry detergents.
Identify communities that can be considered as more vulnerable to pollution caused by large-scale use of laundry detergents.
Evaluate core principles of green chemistry in the industrial manufacture of LAS and its role in designing sustainable surfactants.
Develop a sense of taking ownership by adopting a sustainable action perspective.
Design
The following presentation includes a sequence of content and activities designed for an introductory organic chemistry lecture at the university level. The proposed educational module can be implemented using a jigsaw cooperative learning approach, which we recommend to encourage collaboration and interdependence while dealing with the complexity and cognitive load associated with systems thinking. In this approach, students are grouped into home groups and subsystem groups. Each home group has three students, and each student has a dedicated role to fulfill during the activities, either as a group facilitator, presenter/recorder, or researcher/ strategy analyst. In addition, each group member is responsible for contributing expert subsystem knowledge (societal, environmental, or economic), which they construct together in specialist subsystem groups with members from other home groups with the same role. This design fosters an inclusive environment where each student has an opportunity to fulfill a group responsibility in terms of both knowledge contribution and group dynamics. Following this approach, the proposed lesson would last approximately three 50-minute sessions taught within a two-week time period.
Surfactants.pptxThis example lesson introduces and applies the following chemistry concepts: Structure-function relationships, molecular representations, and functional groups, catalysis and activation energy, isomerism, and properties, the amphiphilic structure of LAS, surface action, intermolecular forces, solubility and concentrations, micelle formation, foaming as an emergent behavior, organic reactions discussed concerning chemical manufacture and biodegradation, ecotoxicity and cytotoxicity.
This example lesson assumes students already have a basic understanding of polarity, intermolecular forces and the influence of carbon chain length and branching, functional groups, including alkanes, alkenes, and sulfonates, catalysis and activation energy, organic reactions including dehydrogenation, alkylation, and oxidation, concentration.
The following diagram depicts a suggested schedule for the implementation of this example lesson:
The example lesson includes a set of interspersed activities (labeled "Let's Think") that students are expected to complete in small collaborative home groups and then share their ideas in whole class discussions. Students will discuss specific slides in their subsystem groups as indicated. These activities ask students to share and explore chemical concepts, actively engage in core science practices like analyzing data, making predictions, applying models, and generating explanations, and practicing systems thinking skills. The specific system thinking skills that each activity may help foster are highlighted using representative icons. They also create opportunities for the instructor to formatively assess student learning and provide specific feedback to advance their understanding.
The teaching is designed to scaffold the development of systems thinking skills firstly by introducing students to the core chemistry concepts, then by enabling them to use the SOCKit tool to visualize the chemistry concepts about the societal, environmental, and economic subsystems, and to then zoom into and out of the chemistry to visualize complex reactions within and between subsystems before constructing a SOCME that shows mostly concepts on zoomed out-level where chemistry is a hidden dimension.
We recommend that some information is presented to the groups as a starting point, but they should draw on their experience, observations, and imagination to expand their understanding of these subsystems and to connect them to the UN sustainable development goals and include additional components that they have identified, document relationships between components and indicate potential changes over time as well as intervention points.
Map Out
During this phase, students are introduced to central chemical concepts and ideas at the macroscopic and submicroscopic levels that help us explain why oil and water do not mix. The proposed activities enable students to acquire and practice concept mapping skills, identify concepts and their relationships, and become familiar with a system mapping (SOCKit) tool. Through this process, students develop an overall view of the nature and complexity of the problem under analysis. This is accomplished by engaging students in analyzing relevant data that helps them identify major components, behaviors, patterns, and relationships.
Zoom In
During the "Zoom In" phases of a lesson, students engage in activities that help them identify the main components in the systems of interest, analyze their properties, and characterize their interactions at levels of granularity that are productive in making sense of the problem or phenomenon under consideration. In the example lesson on surfactants, students first explore the interactions between LAS molecules and ions at a submicroscopic level, before gaining an understanding of complexation and solubility and thinking about how these processes will influence concentration, detergency power, and surface tension. These ideas change the concentration of LAS and are dynamic as students explore in this sample activity:
Zoom Out
Once students model and understand the phenomena of interest at proper levels of granularity, it is important to "zoom out" using activities that help them recognize system-level properties and behaviors that emerge from the interactions between components. For example, in the surfactant lesson, students are asked to evaluate the biodegradation rate of LAS by micro-organisms in ideal and non-ideal conditions and to think about ecotoxicity under different conditions:
Connect
In the "Connect" phases of the lesson, students engage in activities that allow them to apply what they have learned to explore and analyze relevant systems and processes. For each subsystem, the corresponding student groups expand their concept maps during session "3" by adding new concepts, relationships, and interactions within that particular subsystem and identifying connections to chemical systems and processes as illustrated by this activity.
During sessions "4" and "5", students get back into their home groups where they expand on concepts at a zoomed-out level of granularity, where “hidden” cyclic behaviors are identified, and predictions are made as illustrated by the following example activity. In this task, students are asked to analyze how dysfunctional wastewater treatment plants influence LAS concentrations and its biodegradation rate in the environment
Evaluate
The "Let's Think" and apply activities interspersed in the example lesson create diverse opportunities to formatively assess student learning and provide specific feedback to advance their understanding to meet the lesson's learning objectives. These activities also help students evaluate strengths and areas needing improvement in their learning. As part of the summative assessment, we suggest that students in their subsystem and home groups submit their expanded concept maps for individual subsystems and the final SOCMEs they put together in their home groups so that these SOCMEs can be assessed with the following rubric. Students are also asked to reflect on what skills and understanding they have gained, which enables the teacher to informally assess their learning as students think about how human activity has the potential to reduce or aggravate the negative impacts of LAS in the environment and human health and how they play a critical role in the move to more sustainable surfactants.
Reflect
During the implementation of the lesson, it is important to systematically gather information about student learning and performance that can help us critically reflect on aspects of the lesson that need to be modified to support student learning of the central ideas, core practices, and socio-environmental competencies targeted by the lesson.