Salt vs. Sugar – A Dissolving Problem

This formative assessment looks at two household chemicals (table salt and sugar) and compares their properties while looking at how they dissolve in water. The “Salt vs. Sugar” formative assessment explores students’ thinking about the question “How does structure influence reactivity?” The main idea that is being targeted is for students to think about what is happening at the molecular level during the solution process. This activity is important for students because it helps create a context for what some of the vocabulary and concepts mean by providing tangible examples of these concepts (such as the concept of saturation).

Students were guided through the activity with the salt vs. sugar worksheet (if students are unable to perform this on their own sample data can be provided). Students were encouraged to try this activity at home if they had the proper materials (if they did not these data were shared with them). All students were additionally given an album of pictures in the form of a slideshow of an example of the experiment being done in case they did not have the materials at home to do the experiment. The experiment involved adding salt and sugar to two separate cups of water incrementally and observing the changes to the solution. Students would record these observations for each teaspoon of the chemical added. The experiment was done in two separate glasses: one glass of water had the sugar added and the other glass of water had the salt added. Students would answer questions before starting the activity to make predictions, they would perform the experiment (or look through pictures to make their observations), and then answer follow up questions that specifically targeted their chemical thinking with regards to this activity. Prior to this activity was a lesson regarding the vocabulary (saturation, solution, solute, solvent, etc…) and a lesson regarding how to calculate the concentration of a solution or the amount of solute dissolved. The school this formative assessment was given in is a high school in a small urban city. The grade level of students this formative assessment was given to were grades 10 and 11. The school’s racial demographics are about 55% Asian, 35% White (non-Hispanic), and 10% mix of other races and ethnicities. Approximately 30% of the student population is classified as economically disadvantaged. Additionally, 44% of the school population’s first language was not English and 8% of the school population are English language learners. The specific class that this formative assessment was administered to was a standard level, full year high school chemistry class.

Teacher reflections

Because of the asynchronous flow of the remote learning period, this was challenging to be able to fully communicate with my students during this activity to fully understand their chemical thinking as they were working. I think this activity could have worked better in a synchronous remote learning environment, however, because some students may not have access to the materials needed for this activity at home, materials could have been prepared in a way in advance to get them to the students so they could perform this activity at home. Doing it in a synchronous environment could have also led to interesting suggestions, ideas, or follow ups that students might have thought about on the fly as they were doing the activity. Often times, these ideas and thoughts might be missed in an asynchronous environment where students have time to consider their answer in what they deliberately share at the end, and it might be refined and missing elements of their chemical thought process. Outside of the asynchronous vs synchronous challenge of the formative assessment, I found this formative assessment rather successful in giving students an opportunity to explore aspects they know about molecules and how they interact with each other (specifically, polar intermolecular forces) and see if they can make a model or conclusion about why these chemicals dissolve differently.

Remote learning

During the Remote Learning session, Google Classroom was the primary tool for instruction and organization of learning materials. For this specific Formative Assessment, two documents were provided to students: one was a Google Doc with the questions and instructions for the activity, the other was a Google Slides presentation containing several pictures that were taken during a demo of the activity (in case some students did not have access to the materials at home for this activity, they could work with the image slides to make their observations). One consideration to alter this formative assessment would be to convert the questions to a Google Form instead to perhaps make it easier for some students to input their answers, especially if they didn’t have access to a computer but could use a phone (students had indicated that Google Docs can be very difficult to use on a phone’s touchscreen).

Examples of student work

Pre-activity questions

	1. Refer back to your Lesson 1 notes for the definitions for “saturated” and “unsaturated” and reprint the definitions below.	2. Why do you think substances dissolve in the first place?	3. How does a substance dissolve? You may include a picture to help illustrate your explanation.	4. Do you think salt and sugar will dissolve the same way in water? Why do you think they dissolve similarly/differently?
Student 1	Saturated – Holding as much water or moisture as can be absorbed; thoroughly soaked. Unsaturated – (of organic molecules) having carbon-carbon double or triple bonds and therefore not containing the greatest possible number of hydrogen for the number of carbon atoms.	Because dissolve can be said to become broken up or absorbed by something or to disappear into something else. When sugar becomes absorbed into water, this is an example of when sugar dissolves into water.	When a substance dissolves in water, and each water molecule is like a tiny magnet. For a substance to dissolve in water, it must also be a polar molecule, or it must be capable of breaking into polar molecules. For example, when you add some salt in water it can be dissolved into water and become salt water.	No, dissolve differently. I think they dissolve differently because some of the salt did not dissolve and sugar is much more soluble in water than is salt . For example, when you add 8 spoons of salt into water the salt already starts to stay in the bottom of the cup. And, when you add 30 spoons into water the sugar just starts to stay in the bottom of the cup.
Student 2	Saturated - “Completely full”, no more can dissolve, at maximum concentration, if you add more solute, it will remain at the bottom of the solution Unsaturated - Not at the maximum concentration, if you add more solute, it will dissolve still	Maybe because certain particles interact with one another to mix it	A solute breaks from a larger group and separates from one another. screen_shot_2020-08-12_at_3.09.36_pm.png	No, dissolves differently. I think that because the two are different substances, the chemical formula will affect the way they both interact with water
Student 3	Saturated - maximum concentration, if add more solute it will remain at the bottom Unsaturated - not maximum concentration, if added more solute, it will dissolve.	Substances dissolved in a liquid form a solution. This means that the atoms of the dissolved substance are between the molecules of the liquid and cannot be separated by filtration. If you pour a solution of salt and water through filter paper, both the water and the salt will pass through the paper. In this example, the dissolved salt is called the solute, and the water that contains it is called the solvent. Liquids other than water also act as solvents for some substances.	When one substance called the solute dissolves into another substance called the solvent. Dissolving is when the solute breaks up from a larger crystal of molecules into much smaller groups or individual molecules.	Yes, dissolves the same. I think both will dissolve in water.

Post-lab questions