Lesson for a Blind Student:
Lesson for a Blind Student:
Colligative Properties
Colligative Properties
I have chosen blindness as the disability for my special needs learner. According to the World Health Organization, vision impairment is divided into two categories: distance-presenting and near-presenting.1 Distance impairment, which is most relevant for conventional learning settings, includes a range of visual acuities: from mild (6/12 to 6/18) to severe (6/60 to 3/60). Blindness is defined as visual acuity worse than (3/60). Therefore, visual impairment could include a range of limitations. While some visually impaired learners could use corrective lenses or other assistive strategies to minimize the effects of their disability on their learning, blindness will be used for this exercise. For a blind learner, visual aids such as graphs and diagrams cannot be used to explain scientific concepts. Verbal information could be communicated through Braille or using audio, but not through printed text such as a written instruction guide or a textbook.
I am designing a learning strategy for the concept of freezing point depression. Freezing point depression is the drop in temperature at which a liquid (the solvent) freezes when another substance (the solute) is mixed into it. The most easily accessible example is saltwater, which freezes at a lower temperature than freshwater. The concept is also relevant in scientific contexts: chemical products created in a synthetic laboratory might not solidify at room temperature as expected if they are impure. This is an entropic effect. That is, it is related to the level of disorder in a substance. Solidification happens when molecules are able to arrange themselves in a repeating pattern without moving past each other.
At the freezing point, there is an equilibrium of solid and liquid molecules. Liquid molecules attach and detach from a solid surface. When foreign particles are introduced into a substance, it lowers the surface area of exposed particles that can attract like molecules (so the rate at which molecules add to the solid surface decreases), while the ability of exposed solute molecules to leave the solid surface remains the same (so the rate at which molecules leave the solid surface remains constant). The net effect of this is that the equilibrium of solid and liquid at a particular temperature favors the liquid state more when forein particles are dissolved than when the substance is pure; the temperature at which a substance fully freezes gets lower as more solute particles are added. Furthermore, the introduction of irregularities makes it harder for solvent molecules to form a regular structure of intermolecular bonds. When solute molecules have to solidify around the foreign particles, it breaks their optimal pattern of intermolecular interactions.
Often, this concept is explained using graphs and diagrams. Graphs show the relationships between freezing point and solute concentration. Images are used to show how particles intersperse in solution and how this affects the equilibrium of solid and liquid phases. Crystal structures can be shown with graphic representations. These visual aids are typically combined with verbal explanation. For a blind student, this methods of understanding are not accessible.
To address the needs of a blind learner, we could use a tactical demonstration with uniform blocks and foreign objects in a shaking box. This strategy will describe the dissolution of a nonpolar solute in a polar solvent as an example. The uniform blocks in the set-up represent solvent molecules. They should be regular prisms in shape for simplicity, with weak magnets on their surfaces. For example, wooden cubes with weak magnets on each of their six faces could be used. For safety, the corners and edges of these blocks should not be hard: learners will immerse their hands in the box while the box is shaking during the demonstration. The presence of the magnets on the prisms should be perceptible by touch, and learners should be able to familiarize themselves with the magnetic properties of the solvent molecule representations before the demonstration begins. The exposed weak magnets are analogous to sites of intermolecular interaction between polar solvent molecules, like hydrogen bonding that occurs in water.
The smaller set of different objects represents solute molecules. As they are nonpolar in this case, representing molecules without strong intermolecular interactions, they should not have magnets. They should also be small enough to fit into spaces between the solvent blocks such that “frozen” solvent can be arranged around them. For example, rubber balls slightly smaller than the wooden cubes could be used. It should be immediately obvious to the learner that these objects are different based on touch; their texture and shape should both be different enough for blind learners to distinguish them from the solvent. As with the solvent molecule representations, learners should explore the properties of the solute (noting that they do not stick to each other or the solvent representations as well as the solvent representations stick to each other).
Temperature can be simulated using a shaking box. A box should be placed on a platform at the correct height for each learner to put their hands into the box. The platform, when turned on, should be able to shake the box with different levels of vigor to demonstrate different temperatures. Ideally, the intensity of shaking should be controlled with a sliding dial that the learner can manipulate. To begin, pure solvent representations should be added to the box. The shaking box can then be turned on. As the box shakes at high temperature, the prisms will attach and detach from one another due to the vigor of shaking. Learners should put their hands into the box and feel the molecules moving past each other. They can be encouraged to try to form a solid mass inside the box, and should feel that even when they arrange prisms together by hand, the rate at which they break apart is too high for a single mass to form. The shaking can then be decreased, showing lower temperature. The learner should repeat the task of putting prisms together, this time successfully “freezing” the blocks.
To be sure the learner observes relevant details about the demonstration, a guide should explain the demonstration and concepts it represents aloud. This guide should ask questions of the learner as the demonstration progresses, such as, “Was it easier or harder to keep the molecules together that time? Why do you think that is?” This type of conversation should continue throughout the demonstration.
Once the pure solvent has been explored, the learner should reset the solvent molecules in disarray and mix solute representations throughout the box. The experiments with high temperature and low temperature should be repeated. The learner should observe by feel that it is harder to arrange the collection of objects into a “solid” structure at every temperature when there are solute particles getting in the way of intermolecular solvent interactions. At some temperature, learners should be able to arrange the objects into a stable set. They should note, by feel, that the shaking is lower in intensity with solute objects present. This process can be repeated again with even more solute representations to demonstrate that increasing solute concentration corresponds to lower freezing temperature.
This demonstration has the advantage of versatility because the objects involved can be replaced by objects with different properties. For instance, the learning goal can be expanded to show that more polar solvent molecules have higher freezing temperatures. This could be accomplished by introducing solvent representations with stronger magnets. This difference remains accessible to blind learners, as they can feel the difference in magnet strength with their hands.
This strategy is effective because it allows learners to connect with the scientific concept as it exists in the real world. Colligative properties, which inherently deal with the motion of molecules, are often displayed with static images for convenience. Dynamic images such as videos improve upon this, but they are still removed from the truth of the three dimensional environment of matter. When watching a video or looking at a diagram, learners are also forced to accept what they are told about the properties of molecules on faith. With a physical model, learners can feel those properties for themselves. Properties of physical things – such as temperature and intermolecular interaction – can be apprehended more quickly when they are encountered in a physical setting as opposed to a static or virtual one. A tactile demonstration enables intuitive understanding for seeing learners as well as blind learners.
World Health Organization. (2021, October 14). Vision Impairment and blindness. World Health Organization. Retrieved February 17, 2022, from https://www.who.int/news-room/fact-sheets/detail/blindness-and-visual-impairment#:~:text=Distance%20vision%20impairment%3A,acuity%20worse%20than%203%2F60