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What I am doing?
What am I observing?
This lesson is the first of a sequence in which students will learn to make their own ''Rock Candy''. In this first inquiry, students will learn that in order to form a ''Rock Candy'', you have to create a supersaturated (a solution in which no more sugar can dissolve) solution by heating a sugar solution. In the next lesson, students will see that as they allow their solution to cool, sugar crystals will form: this is how rock candy is created.
At the end of this lesson, students will understand the concepts of solutes, solvents, solutions, dissolution and supersaturated solutions. The next focus of this unit would have students explore the formation of crystals and the concept of precipitation which occurs when a solute transf ers from a liquid solution to a solid crystalline susbtance. The grade level for this inquiry is directed at Cycle 3 or Grade 5 or 6.
During a demonstration of the first portion of the inquiry (teacher's rock candy), the teacher will draw students' attention to the supersaturated nature of the solution which contains more solute (sugars) than the solvent (water) can hold. This will lead to our driving question:
Does sugar perpetually dissolve in water?
I think that a solution becomes supersaturated when a large quantity of a solute is added to a solvent. I think this because I have read it in scientiftic literature (https://www.alloprof.qc.ca/fr/eleves/bv/sciences/la-dissolution-s1053) about solvents , solutes and solutions.
I also believe this because I have undertaken the Rock Candy inquiry and seen that there are more particles of sugar than the water can dissolve meaning the solution created is supersaturated.
Evidence 1: Jellow powder dissolves in hot water
Evidence 2: Rock Candy Experiment: Sugar dissolved in water
Evidence 3: Article and video
There are a number of examples of dissolution in everyday life that are easily observable such as sugar dissolving in coffee and salt dissolving in hot water. If we add more and more of these substances eventually they would not dissolve anymore. These contentions are verified in academic literature, such as the article on Alloprof! and the Rock Candy inquiry works to witness dissolution and what occurs when a solution becomes supersaturated.
The students will have some previous knowledge that will guide them through this inquiry on supersaturated solutions. Previously, students would have been introduced informally to the topics of : solution, solute, solvent, solubility and dissolution which they constantly have a chance to observe through real life examples. For instance, when mom puts sugar in her boiling water for the tea the sugar disappears! Why? ?Because when sugar is mixed in water its particles separate and goes in between the water particles. The water in this particular situation is the solvent and the solute is added to the solvent. In this case it is the sugar. If the solute dissolves (disappears) it is soluble and we make a new solution.
Some other examples may include:
Non-normative ideas could include:
In this sense, it is probably that students will be unaware of the factors that will help the solute to dissolve.The teacher will have to place a special focus on 4 of those factors:
The educator can give them specific examples that they will be able to relate to. For example: when I want more lemonade I add more water, sugar and lemon (quantity of solvent). Sugar dissolves very fast when mom heats up my milk and stirs it ( heating and mixing). If I am patient, I can see the Kool-Aid powder dissolving in water (time).
Students could still have some doubts on how sugar dissolves in water. How can this happen with water and sugar but doesn't with water and sand? The educator must address two factors here : temperature and solubility. Some solutes are water loving and some are water fearing. If a solute is water loving and dissolves it is soluble. The teacher could take the example of water and sand (mentioned by the children) and indicate that the sand does not dissolve in water the waves simply wash it away. Finally, when we heat up water, the water molecules spread apart. Thus, leaving a lot of space where we can add the sugar into. We could ask students to draw a model of the molecules of water and sugar and explain the process of the solution through their drawing.
Moreover, students may still not understand what happens if we increase the amount of a solute in a solution. They might be confused because they just learned that a soluble solution should completely dissolve the solute. Consequently, they could claim that a solution will never be supersaturated because they will always be more solvent (water) than solute (sugar). The teacher must be very careful and clear about this concept and explain that a solution is saturated when the liquid holds as much of the compound dissolved in it as possible. For example, when making rock candy, you dissolve as much sugar as possible in water to make a saturated solution. If you add more compounds than can dissolve in the liquid, the undissolved bits remain as solids in the liquid. This could be addressed by bringing to their attention what will happen when they put a handful of sugar in a tiny playdough cup.
This portion of the lesson is designed to focus the attention of the students on the process of dissolution and its effects.
TEACHER: Today I will be showing you the first few steps of the experiment that you will be doing a little later. I will be adding sugar into warm water and stirring and that is all I am going to tell you for now. Take time to watch what I am doing and take notes on what you hypothesize is happening.
***Demonstrates the steps***
***Wait 2 minutes***
TEACHER: Is there anyone who would like to share what they found interesting when watching the beginning of the experiment.
STUDENT 1: I noticed that you put a lot of sugar into the water.
TEACHER: Did anyone else notice that?
STUDENT 2: Yes! I also noticed that at first the sugar disappeared completely but as you added more it did not disappear.
STUDENT 3: I saw that too! The water was clear and by the end the water was sort of cloudy.
TEACHER: So what you are saying is that sometimes the water cannot make the sugar disappear. Do we think that the sugar is disappearing?
STUDENT 2: I think that the sugar stays in the water because when I make juice the water starts with no taste but after we add the powder there is a taste.
TEACHER: What a nice connection! Can someone explain what STUDENT 2 just said?
STUDENT 4: STUDENT 2 just said that when they add powder to water when they make juice that the water has a flavour when before it did not have any flavour so the taste stayed in the water.
TEACHER: Do you agree with STUDENT 2?
STUDENT 4: Yes because it looked like the water got really cloudy at the end.
TEACHER: Have you ever done something similar to what I just did at home?
STUDENT 3: My mom sometimes adds sugar to her coffee and stirs it.
TEACHER: Very interesting. Would anyone like to give another example?
STUDENT 2: I make juice from powder at home. Sometimes it's blue!
TEACHER: Alright those were some very good examples. What do you think happened in those cases to the sugar and the powder in the coffee and water? I will give you one or two minutes to finish writing your thoughts and then we'll share our ideas.
In this portion of the lesson students will carry out the first portion of the Rock Candy inquiry using the investigative question developed by the class and they will collect data.
During this section the teacher will circulate around the classroom and ensure students are on task. Reminders about writing notes in the science journal will be necesssary as will some reflections on whether students are making observations or inferences.
This part of the lesson requires students to organize their observations and present them in meaningful ways. Through the discussion of results and the development of more scientifically accurate models students will create claims, present evidence and reason their claims to explain their understanding of the phenomena.
TEACHER: Can you tell me about what you are observing here? Do you have ideas as to why you observed what you did and do you have any evidence to support your ideas?
***STUDENT 3 describes their model***
TEACHER: Can someone repeat what they just said?
***STUDENT 4 repeats the description of the model***
TEACHER: Thank you STUDENT 4! Do you agree or disagree with that model? Remember to use examples to support your point of view.
TEACHER: Would anyone like to add on to what they just said?
***While students provide feedback, the teacher will rephrase comments, ask for more evidence when necessary and ask for justification on conclusions.***
Once the presentations of the models are finished the teacher will ask how those models speak to one another by pushing students to look for similarities and differences.
A liquid mixture where the solute is evenly distributed in the solvent.
A solid (sugar/solute) becoming incorporated into a liquid (water/solvent) and forming a solution
When solute can no longer dissolve (or be absorbed) into the solve, creating a solution with undissolved substances at the botton. In other words, the solutionhas the max amount of solute that can be dissolve into the solvent.
When the solute dissolves completely into the solvent with no substances remaining undissolved.
A solution that contains more than the max amount of dissolved solute than the saturated solution.