The Rock Candy Inquiry (Part 1): Supersaturated Solutions
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90 minutes
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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.
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L'univers matériel
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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.
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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?
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CLAIM:
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:
Evidence 1: Jellow powder dissolves in hot waterEvidence 2: Rock Candy Experiment: Sugar dissolved in water
Evidence 3: Article and video
https://study.com/academy/lesson/concentration-saturation-lesson-for-kids-definitions-examples.html
https://www.ck12.org/c/chemistry/supersaturated-solutions/lesson/Supersaturated-Solutions-CHEM/
REASONING:
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.
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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:
- Salt dissolving in water when cooking pasta;
- Lemonade: Sugar is the solute, water is the solvent and the solution is lemonade
- Sand does not dissolve in water, it is not soluable
- Kool-Aid powder
Non-normative ideas could include:
- When solutes are mixed in a solvent they dissappear
- A solute will always disappear at the same rate.
- It doesn't matter if the solution is hot or cold.
- Mixing a solution is a waste of time. It will dissolve anyway
- When solutes can effectively dissolve in a solvent it will always be soluble! It doesn't matter if we add more or less solvent. It doesn't matter if we had more or less solute
- The amount of solute particles remaining at the bottom of a container will always eventually dissolve
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:
- Quantity of solvent
- Heating
- Mixing
- Time
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.
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Teacher Materials
- For Students
- 1 wood skewer per student
- 1 clear jar per student
- 1 spoon per student
- 250ml water per student
- 750g of sugar per student
- Additional sugar for coating skewer
- Large sheets of paper
- Markers
- For Teachers
- Kettle
- Scales
- Tape
- Whiteboard markers
Student Materials
- Per student:
- Science journal
- 1 wood skewer
- 1 clear jar
- 1 spoon
- 250ml water
- 750g of sugar
- Additional sugar for coating
- Per team of 4:
- Scale
- 3 large sheets of paper
- Markers
- For Students
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This portion of the lesson is designed to focus the attention of the students on the process of dissolution and its effects.
The teacher will:
- Demonstrate the first steps of the Rock Candy Experiment.
- Instruct students to take notes in their science journals concerning their first impressions of what is occuring and how.
- The teacher will solicit student predictions about what they believe was happening to the Rock Candy inquiry.
- Students will give a number of responses which are reflected in the "anticipate student ideas" section of the lesson plan.
- Be prepared to rephrase student ideas and invite other students to add on or engage in discussion.
- Elicit student ideas about dissolution by asking:
- Have you ever made Kool-Aid with powder?
- Have you ever seen your adult put sugar in their coffee?
- What happened to the solid that went into the hot water?
- In groups of 4, ask students to create a visual model of what they believe is occuring when the sugar is added to the water.
- See ideal model in Anticipating Students' Ideas
- Co-create an investigative question that will be the basis for the rest of the lesson.
- Ask students if they need any clarification surrounding the experiment before beginning to create the investigative question.
- If there is clarification needed, repeat the principles of the experiment.
- If there is no clarification needed, have students provide potential investigative questions that relate to solutions and saturation.
- Give students sufficient time to generate their own questions?
- Write all questions on the board and develop a single investigative question that the class will investigate during the "Explore" phase of the lesson.
- The question should be relevant to supersaturated solutions and testable.
- As an example, "when does a solution go from saturated to supersaturated? is a testable question. We can hyptothesize an answer and test.
The student will:
- Watch and take notes in their science journal of their initial predictions and ideas about the processes that are occuring during the video.
- They may choose to do this however is most condusive to their udnerstanding.
- Provide insights to the teacher based on their initial predictions from the demonstration and their prior knowledge about solutions, solvents and solutes.
- Provide examples of times that they have seen a substance dissolve in a liquid.
- They may bring up times when they failed to dissolve a substance in a liquid (Kool-Aid that did not dissolve completely when too much power was added)
- In groups of 4, using the piece of paper provide students will represent the sugar-water solution with clear water and sugar molecules.
- Provide potential investigative questions that they have concerning dissolution.
- Demonstrate the first steps of the Rock Candy Experiment.
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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.
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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.
The teacher will:
- Remind students of the investigative question to focus attention and then present the steps of the Rock Candy inquiry.
- Read each step with time allowing for questions and clarifications.
- Reiterate the scientific equipment necessary with special attention focused on equipment to measure quantity (scale).
- Further remind students that they can undertake the experiment twice, with each partner taking turns to be the primary experimenter and the notetaker.
- The notetaker should be making observations in their science journals.
- As students conduct the experiment, move through the class answering questions, ensuring safety and keeping students on task.
The student will:
- Listen to instructions and ask questions for clarification.
- Undertake the Rock Candy experiment using the following directions:
- Step 1: Take a large glass jar and place it onto a clear surface.
- Step 2: Take 1 wooden skewer and 1 clothespin, then clip the clothespin to the wooden skewer so that the wooden skewer hovers inside the glass about 1 inch (2.5 cm) from the bottom of the glass. Remove the skewer and the clothespin from the glass and leave aside.
- Step 3: With guidance from your teacher, pour 250ml of water into a kettle and bring the water to a boil (this will take approximately 3 minutes)
- Step 4: Once the water is boiling,transfer the water to your jar and add the first interval of sugar. Stir until the sugar dissolves.
- Step 5: Slowly continue adding more sugar at intervals of your choosing while stirring each addition of sugar until it disolves. Once no more sugar will dissolve in the water let it cool for 20 minutes.
- Be sure to write how much sugar is being added to the mixture in your journals.
- Also note how many times you added sugar.
- Step 6: Once the solution is cooled, submerge the skewer into the jar assuring that it hangs down without touching the edges.
- Step 7: Allow the jar to cool fully and leave it in a clean area.
- This procedure is now complete.
- Remind students of the investigative question to focus attention and then present the steps of the Rock Candy inquiry.
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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.
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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.
The teacher will:
- Have students classify their observations on the student protocol document.
- During this period the teacher will circulate and facilitate group discussions by answering questions and asking students about what they have observed in the experiment.
- Direct students to create 3 models on a large piece of paper for each group. The models should have appopriate labels and include explanations of their data. Refer to the ideal model shown in the clain section of:
- The unsaturated solvent
- The saturated solution
- The supersaturated solution
- Encourage a short presentation from each group about their model.
- Once the presentations are complete hang each model on the board and have students draw comparisons between the models.
- Draw attention to quantities of sugar, number of stirs and other quantitative data.
- Create a consensus model from the models presented.
- Solicit the input of students about what should and should not be included in each model (unsaturated, saturated, supersaturated).
- Ensure that students are providing justifications and explanations for what is being included in the model.
- "What do you mean?"
- "How do you know....?"
- "How can you show...?"
- Encourage students to build on each other's ideas so that one consensus is developped.
- Introduce the correct scientific vocabulary using the lexicon provided.
- Have student complete the Claim, Evidence and Reasoning section of their journals individually using the observations taken during the experiment, the consensus model developped and the other resources explored during the period.
- Once this is completed students may verify with another classmate and engage in some debate .
- Students may present their Claim, Evidence and Reasoning page to the class.
- Respectful debate should be encourage and facilitated.
- Be sure to rephrase, clarify and push for more reasoning whenever necessary.
- Correct only for major errors in reasoning.
- Provide a final challenge question for students to consider.
- Ex: Do the concepts studied here also apply when you use a bath bomb? Is there a way we could study the phenomenon in class?
- Ex: In a supersaturated solution, what happens to the "leftover" solute?
The student will:
- In groups of 4, students take their observations and organize them in a manner that will allow them to make meaningful interpretation of the data through the identification of patterns.
- In the same group, the students will create their models and prepare a short presentation of their representations. They should also include a small written report of their models on the back of the sheet of paper.
- Each group will present their model briefly in order to explain what they observed during their experiment.
- Present what they believe should be included in the model and provide a justification for their claim.
- Complete the Claim, Evidence and Reasoning section of their journals individually.
- Once this is done they may consult with one other classmate briefly.
- Engage in respectful debate about their classmates' claims, evidence and reasoning.
- Have students classify their observations on the student protocol document.
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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.
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During presentations:
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.
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Solution:
Dissolve:
Saturated Solution:
Unsaturated Solution:
Supersaturated Solution:
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.
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- ALLOPROF (2020). Sciences: La dissolution. Récupéré de : https://www.alloprof.qc.ca/fr/eleves/bv/sciences/la-dissolution-s1053
- CHEMISTRY : LIBRE TEXTS (2020). Types de Saturation. Récupéré de : https://chem.libretexts.org/Bookshelves/Physical_and_Theoretical_Chemistry_Textbook_Maps/Supplemental_Modules_(Physical_and_Theoretical_Chemistry)/Equilibria/Solubilty/Types_of_Saturation
- MAKEMEGENIUS.(20 decembre 2013). Solution, Solvent and Solute. Récupéré de: https://www.youtube.com/watch?v=e-2EoyDYamg&ab_channel=makemegenius
- SCIENCEBOB.(2020). Make your own Rock Candy. Récupéré de : https://sciencebob.com/make-your-own-rock-candy/
- MYCOURSES. (2020). Talk Moves document. Récupéré de : https://mycourses2.mcgill.ca/d2l/le/lessons/464669/topics/5189124
