How Sweet it is

pitcher of sweet juice and another of unsweetened juice

This formative assessment (FA) task targets chemical identity. The main idea of this formative assessment is solution concentration. This FA is an easy way to get students interested in the topic of concentration because making juice is accessible to all learners. By asking students to think about a strategy for making juice of a desired sweetness, explain why that strategy works and then draw particle pictures to compare the juices, students were able to think more critically and reveal their chemical thinking. Since the concept of concentration had not been taught yet, the words “sweet” and “less sweet” are used in place of the words concentrated and dilute. In the FA, Nassir prefers the taste of sweet juice (dark red) and his Mom prefers it to be less sweet (lighter red color).

This task was presented as a Do Now and students are asked to use materials provided to make Nassir and his Mom’s juices and answer questions about them. The juices should look like the pictures. The materials provided are beakers, graduated cylinders, spoons, water, and Kool-aid powder in small dixie cups. Students are allowed to use other materials from the classroom (e.g. a larger beaker) if they want. Students receive the PDF icon  handout to guide and record their answers. This was printed in color so they could clearly see the colors of the juices.

The day before this task, students learned about mixtures and were introduced to vocabulary words pertaining to mixtures. Included were: solution, solvent, and solute. Students found examples of solutions at their house for homework and had to identify the solute and solvent in each. The concept of concentration (and how to calculate molarity) was taught the next day. It was helpful having done the juice activity with students because it is referred back to numerous times throughout the rest of the week. For example, as a bridge to concentration: what if we can’t identify the solution by its “sweetness”? What if it’s salt in the beaker so the property of sweetness doesn’t apply? Or if it’s saltwater and therefore colorless, then how would we know which solution was stronger (besides by tasting)? We can calculate molarity, which measures how strong or weak the solution is (this is called concentration).

This FA task was tested with high school chemistry students at a school specifically designed to serve a diverse student body of English language learners. All students at the school are newly arrived in the U.S., and many have had little or no schooling in their home country or have had an interrupted education. The school provides a college preparatory curriculum designed to teach students English while also teaching rigorous content including several AP classes.

 

Teaching reflections

Possible follow up/extensions depending on your purpose and what’s observed in class or in student work:

  • Ask students to share out their methods for creating the juices. For example, when making Nassir’s Mom’s juice, did groups decide to pour out Nassir’s juice and start over? Or, did they add water to Nassir’s juice? How is it possible that both strategies could achieve the same result?
  • Spend time talking about the particle pictures. How did you decide to make each picture? What did you realize was important to think about when you were making the particle pictures (the solute, the solvent, or both)? How do your pictures compare to each other?
  • Provide students with correct particle drawings for both juices. Ask them how these compare/contrast to what they drew and have a discussion about the arrangement of the particles in solution (ex: many students drew what looked like heterogeneous mixtures rather than solutions).
  • Show students two juices that have the same intensity of red color (i.e. concentration), but that contain different amounts of solute and solvent. Ask them to think about how the juices could still be equally as sweet as one another.
  • Besides sweetness, are there any other properties that are different in both juices you made today?
  • What if instead of Kool-aid powder your solute was salt. How would you be able to tell two salt solutions apart? How would you know which is stronger (besides tasting)?

 

Examples of student work

Student 1

What did you do to make your sweet juice? We put 25 mL of water and we put a lot of juice mix to get in this color.
What could you do to the juice so that Nassir’s Mom likes it, so it is less sweet? We still put 25 mL of water but we put less quantity of juice mix.
Why do you think this strategy works? This strategy works because it is based on the quantity. If we put more juice mix the solution will be more sweet, and if we put less juice mix the solution will be less sweet. Or if we put more water the solution will be less sweet, and if we put less water the solution will be more sweet.
What do you imagine the particles would look like in the sweet juice? student 1 sweet juice
What do you imagine the particles would look like in the less sweet juice? student 1 less sweet
Explain how you came up with your drawings. If we have more water and less juice mix we will get a less sweet juice. And if we have less water and more juice mix we will get a sweetest juice.

 

Student 2

What did you do to make your sweet juice? I put a little bit of juice mixture (2 and a half tablespoon) and a lot of water (80 mL).
What could you do to the juice so that Nassir’s Mom likes it, so it is less sweet? Add a lot of water in the mixture to make it less sweet.
Why do you think this strategy works? It works because when there is less amount of solute and more amount of solvent. The energy of the solute reduces so the juice is less sweet and the color is different.
What do you imagine the particles would look like in the sweet juice? student 2 sweet juice
What do you imagine the particles would look like in the less sweet juice? student 2 less sweet juice
Explain how you came up with your drawings. Nassir’s juice: there have to be more JM in order for the drink to be more sweet.
Nassir’s Mom: There have to be more water particle than JM in order to have less sweet drink.

 

Student 3

What did you do to make your sweet juice? We add more Kool-aid to the water then the sweet juice and the color became red colored each time we add the Kool-aid.
What could you do to the juice so that Nassir’s Mom likes it, so it is less sweet? We add less Kool-aid than sweet juice, so the color was not really red, and the taste I think it’s not sweeter too much.
Why do you think this strategy works? The color of the mixture will be based on the quantity that the Kool-aid that we add. More Kool-aid, more sweeter, more red color. Less Kool-aid, less sweet, less red color.
What do you imagine the particles would look like in the sweet juice? student 3 sweet juice
What do you imagine the particles would look like in the less sweet juice? student 3 less sweet juice
Explain how you came up with your drawings. Nassir’s juice has more sweet Kool-aid, so the solute (Kool-aid) is more than water because the red color is too much. Nassir’s Mom’s juice has less red color, so less solute Kool-aid, so it has less sweet and more water solvent particles than the solute Kool-aid particles.