Exploring Concentration

2 glasses containing solutions, one has particulate level modeling

The “Exploring Concentration” formative assessment (FA) asks students to make their “ideal” Kool-aid solution and to make variations of their recipe to explore the different variables of concentration. This FA targets chemical control by allowing students to experience the processes and effects of changing concentration. This will take them into learning about chemical reactions and how to produce more or less of a product by adjusting concentration. The FA focuses on introducing molarity so that students are able to have a real world example of each variable (molarity, moles, and volume) to use while doing stoichiometry in the following lessons.

In the FA task, students use a PDF icon  to guide their activity. They are provided with clear cups, plastic spoons, small cups for tasting, and Kool-aid powder. Students, working in groups of 2-3, are tasked with creating their “ideal” Kool-aid solutions and represent their solution on a particulate level. They then alter variables such as the amount of water and the amount of Kool-aid powder, each time adjusting their particulate representation to match the macroscopic changes. The students then have to generalize their “ideal” recipe so that I can be made for any amount.

This FA task was tested with 11th and 12th grade chemistry students, during a unit on chemical quantities. This assessment was designed for both students on Individual Educational Programs (IEPs) and a large population of English as a Second Language (ESL) students. I have included illustrations and graphic organizers for the wide variety of learners at one of Boston’s traditional high schools. In the class in which it was tested, the students had recently learned about the mole and how to conduct mass to mole conversions. This formative assessment was a way to introduce students to solutions and molarity and for students to see how much they already understand about concentration while tying it to the number of molecules in a solution.

Teaching reflections

Students enjoyed this activity and had a lot of prior knowledge to bring about concentration. They were able to predict what they thought would happen after changing the variables and it really helped when we started talking about the math portion. It gave students an entry point when they started solving molarity calculations because they could understand that when I dilute something that I am not adding any new molecules but just changing the volume which lowers concentration. They were able to see this both happen in their real world and through the math. I also liked having them draw their molecules because it forced them to think at the molecular level about how concentration relates to how much stuff there is per volume.

Some things I will adjust in the future:

  1. When students get to the back side of the worksheet, I would have them draw before and after pictures for questions 1 and 2. I think it was needed to show how exactly the variables changed. I noticed I wanted a more targeted answer. So for each question I think I would add:
    1. Draw before and after
    2. What changed: Did the concentration go up, down or stay the same? What happened to the molecules when you did this? What happened to the volume when you did this?
  2. Question #4: I would move it to the bottom of the front page of the worksheet – It didn’t feel like it had students thinking at the end of the activity and felt like it was needed earlier.
  3. I would add 1 more extension question to replace number 4 about adjusting the variables differently.

 

Examples of student work 

RedHeadMami’s response

 Cups 

 Volume  

 H2O (mL) 

 Spoonfuls 

Observations:

What did you observe? Too sweet?

Too diluted? Is it ideal?

Drawings:

  Draw as many molecules as you think

are in  the cup and adjust how many

molecules of sugar

there are for each trial.

       1                   150 mL                    1            

 It was kind of clear, the red wasn’t too strong.

There was barely any flavor.

  trial 1    

2 150 mL 3 Red was intense. Sweet but not excessively.
Ideal.

Red 2

3 150 mL 2     Red, kind of intense. Not as sweet as I’d like it.    

Red 2

 

NationBaby’s response

 Cup   

Volume  

 H2O (mL)  

 Spoonfuls 

Observations: What did you observe?

Too sweet?  

Too diluted? Is it ideal?

Drawings:

  Draw as many molecules as you think  

are in  the cup and adjust how many

molecules of sugar

there are for each trial.

         1                     150 mL      3 Too sweet

          trial 1                    

2 150 mL              2                          The color is lighter at it tastes                    

Nation 2

3 150 mL 4 Ideal solution.

Nation 3

 

SOSO's response

 Cup 

 Volume

H2O (mL)

  Spoonfuls  

Observations:

     What did you observe? Too sweet?     

Too diluted? Is it ideal?

Drawings:

  Draw as many molecules as you think  

are in  the cup and adjust how many

molecules of sugar

there are for each trial.

         1               150 mL      2

      The color was not very dark and it

                            was like sour.                               

           trial 1                   

2         150 mL         1

  The color was like a light

red and not sweet at all.   

SOSO

3 150 mL            3            

The color was very dark and

really sweet.

SOSO

 

1. PREDICT: If you divided your “ideal” solution of Kool-Aid into two separate cups, would the two solutions taste the same? Explain. 

                   RedHeadMami                         Yes it does have the same flavor because we didn’t add or take away  anything, we just separated it equally.   
NationBaby   Yes it would because the water is still the same.
SOSO   Yes, if they had the same amount of water and the same amount of powder it will taste the same.

 

2. What if you added 100 mL of water to one? What if you added a spoonful of Kool-Aid to the other? Draw and explain (Use your drawing from your ideal solution).

RedHeadMiami Response

Add 100 mL of water: Add 1 spoonful of Kool-Aid

Red 100

Red spoon

We still have 15 molecules of Kool-Aid, but the solution

turns a little more clear because we added water and

                                         we lose some of the sweetness.                                        

  We now have 25 molecules of Kool-Aid in only 75 mL of water,

                    the solution is bright red and very sweet.                             

In lab, try it out. Change your solutions and taste each of them. How are they different now? Record below.

                                            Same as above.                                                                                                      Same as above.                                                  

 

NationBaby Response

                                            Add 100 mL of water:                                                                                     Add 1 spoonful of Kool-Aid                                     

Nation 100

Nation spoon

The molecules would stay the same but the taste will change.    There would be more molecules so it will taste sweeter.

In lab, try it out. Change your solutions and taste each of them. How are they different now? Record below.

                                                 Less sweet                                                                                                               Sweeter                                                         

 

SOSO Response

Add 100 mL of water:                                  Add 1 spoonful of Kool-Aid                                     

SOSO 100

SOSO spoon

          The taste it’s not as sweet anymore, the molecules would not change.          

          The molecules decreased because you added more Kool-Aid.     

The amount of water did not change. 

In lab, try it out. Change your solutions and taste each of them. How are they different now? Record below.

                                  The color looks different, it’s lighter.                                                       The color’s darker because there are more molecules.                 

 

3. Your friend tried your “ideal” Kool-Aid solution and she LOVED it and wants you to make it for her party. Your friend who invited you said that you are going to need enough Kool-Aid for  100 people (about 4,000 milliliters –  equivalent to a punch bowl). How do you create your “ideal” Kool-Aid solution for the whole party?

     ReadHeadMami     

150 x 27 = 4,050 approx. 4,000
3 x 27 = 81 scoops
To make a punch bowl of ideal Kool-Aid I multiplied 150 x 27 because it is approx.

4,000 mL, so I also multiplied 3 x 27 which means I need 81 scoops for 4,000 mL of water.

NationBaby

                                                                              4,000/150 = 26.67 x 4 = 106.66                                                                                   

SOSO

(blank)

 

4. So, another friend in California wanted your infamous “ideal” solution to make different amounts of Kool-Aid. What general recipe would you send your friend so they can make any amount of your “ideal” Kool-Aid solution?

      RedHeadMami         

For every 1,000 mL of water, you need 21 scoops of Kool-Aid

NationBaby

               Get a cup and fill it up to 150 mL and add 4 flat spoonfuls and mix.                  

SOSO

(blank)
Concepts: