Teaching Moles through Beans

Mole activity using beans

"What are we doing to help kids achieve?"

The concept of the mole has always been a challenging topic for myself and my students. The challenge comes in part when we try to imagine 6.02 x 1023 of anything. Another challenge for some students is the math and theory behind this number and concept.

Years ago I started using and tweaking an activity found in an old version of Zumdahl’s “World of Chemistry” textbook. Students start with four different type of beans. They count 50 of each bean and find the mass of each set. Students use the mass of 50 of the smallest bean and divide all of the other masses by this number. They then get the “relative” masses compared to the smallest bean. Some sample data is shown in Table 1.

 

Table 1 - Students find the masses and relative masses of sets of 50 beans of four different types.

 

In the above example, 50 lentils had a mass of 2.43 grams. Fifty white limas had a mass of 14.5 grams. 14.5 grams divided by 2.43 grams is 5.97. This is the “relative” mass of the white limas as compared to the lentils. The relative masses of the other beans were calculated in the same manner. They were all compared to the lentils. Students had just done an activity prior to this in which the examined data that showed that as long as you are comparing the same number of items, you are also comparing the same mass ratios.

Here is where I “tweaked” the published activity. My students were instructed to carefully place on a scale for each bean an amount of beans that would get them to the relative mass for that bean. As an example, they had to place an amount of lentils on the scale to get to one gram. They then had to place white limas on the scale to get to 5.97 grams. They would repeat this for the pintos and black beans. Now the emphasis was on a simple question. Will the number of beans in the end for each relative mass in grams (which by the way was given the unit "a pot") be the same or different for all the beans? You can see some sample data in Table 2.

 


Table 2 - Finding the number of beans with a mass equal to the relative mass of each type of bean.

 

In the end, students saw that the same number of beans would provide the same ratio of masses of beans (Table 1). The opposite is also true. The relative mass of the beans in grams would provide the same numbers of beans which is about 20 (Data Table 2). If they did not want to count out a bunch of beans, they could just count by using the relative masses and a scale. This provided a great model for the mole. It took awhile but it was an easy transition from the relative masses of atoms and amu's to molar mass and the mole.

Moles seem to be tough for students and teachers. Do you have a great mole activity? Please share….would love to take a look.

 

Join the conversation.

Comments 12

Kaleb Underwood's picture
Kaleb Underwood | Tue, 02/13/2018 - 17:30

Hi Chad, 

I do a similar activity with beans in my classes, though I do not have the relative mass aspect included. I am going to add this to my version right now! I based my activity on this activity from AACT. 

It provides a great anchor for the rest of the unit as students continue to try to understand moles and relative masses. The number of times I say something similar to "silver atoms are like kidney beans, and hydrogen atoms are like lentils." I highly recommend activities such as this as an intro to the mole for any chemistry class.

 

Chad Husting's picture
Chad Husting | Wed, 02/14/2018 - 13:37

Kaleb - Thanks for sharing.  I like the AACT activity better.  It has the questions phrased better than the ones that I have.  Might have to use this for next year.   I totally agree that it is a great anchoring activity.  Thanks again.

Jordan Smith's picture
Jordan Smith | Fri, 02/16/2018 - 08:04

I've found students struggle with the relative mass idea when it comes to molar mass.  I'd like to try this idea!  Would you be willing to share the writeup you use with students?  

Radhakrishnamurty Padyala's picture
Radhakrishnamur... | Sun, 02/18/2018 - 08:20

Dear Prof. Chad Husting,

Your method of teaching the mole is very interesting.

There are a large number of articles in recent literature on the redefinition of the SI Base Unit Mole and its connection to Avogadro constant. I contributed my research on this topic in an article, that I think would be of interest to you. You may see it here:http://viXra.org/abs/1801.0429 

Spectroscopy So... | Sun, 02/18/2018 - 19:59

In my teaching of chemistry, I used to provide students with a "Mole Conversion Chart" to assist them in making conversions into and out of moles with number of particles, mass and gas volume. 

Erica Posthuma-Adams's picture
Erica Posthuma-Adams | Tue, 02/20/2018 - 19:34

Hi John,

I have used something similar to the chart you shared as well. While I recognize that charts like this can help students to arrive at mathematically correct answers I have found students can rely on these "tricks" so much they don't actually learn the chemical concepts behind the mole or molar relationships. They can simply plug numbers into an alogrithm and out pops an answer.  I have adjusted my instruction to encourage students to build a strong conceptual understanding of these fundamentals. Using tools like BCA tables and "for every statements" my students understand the mole and stoichiometry in a way they never did when I provided them with a mole map. I encourage you to check out the two blogs I linked here :) 

Kaleb Underwood's picture
Kaleb Underwood | Wed, 02/21/2018 - 16:36

I also used a "mole map" of sorts for several years but have avoided it the last couple of years as I try to move away from tricks towards a greater conceptual understanding. I'm excited about the progress I've made with the mole, and want to check out Chad's lab he references in his comment. Using proportions and "for every" statements has helped tremendously, so has using the lab activity described in this post! My students have a much better understanding of the mole than they ever did (and my old students could get the right numbers!). 

Of course, students find such aids on the internet and from tutors and if it helps them get the write mathematical answer then thats one piece of the puzzle, but if they don't understand why they're doing the math they're doing then they don't yet have a complete understanding. For students who are over-reliant on these types of aids and claim "I can only do the problems with my mole map" then I work with them to help build in the conceptual framework and then challenge them to make their own graphic organizer that incorporates some of the conceptual aspects.

Ah, the mole. What a wonderfuly useful concept and one that gives our students some of the biggest troubles. 

 

Chad Husting's picture
Chad Husting | Wed, 02/21/2018 - 05:37

First, I like BCA tables and "for every statements".    I have to say... I have kids with a super wide range of abilities.  In an ideal world I would love to do BCA tables and have kids internalize "for every statements".  For some kids, I am just not able to get them there.  They can do the mole map.  Part of it is that I have to pick and choose my battles.  Honestly, I constantly loose sleep over it....that's why I write blogs and shamelessly steal ideas from anyone I can.  Not to throw another wrench in the system but I did Argument Driven Inquiry for the first time on, of all things, moles.  Funny thing happened...some of the kids solved for moles in ways I have never seen in 20 years of teaching...but they got the correct answer.  Highest test scores ever in this topic with this particular group of kids.  Here is an idea...maybe it might be interesting to offer methods of solving problems but to utlimately let them discover the method that works for them.  Just something to toss up the flag pole....still trying to figure out this teaching thing....

Kaleb Underwood's picture
Kaleb Underwood | Wed, 02/21/2018 - 17:04

I think letting studetns figure out their own way is huge. I prefer proportions when I set up mole calculations, and most of my students will use proportions. I will happily expand upon the superiority of proportions to dimensional analysis if anyone is curious or unfamiliar. 

But the point is that some students will use dimensional analysis, some will use the algebraic relationshiop n = m/M, and those who really "get it" intuitively will just multiply and divide as appropriate. Of course, all have to show work and label all of their numbers. You do not have to show the work like I do, but you do need to show your work and label!

This variation was hard for me to get used to, but it is really beneficial for students. What is important is that they understand the material. Of course, some students "need" a nice structure, and if that is the case then I tell them to follow me! :)

Chad Husting's picture
Chad Husting | Thu, 02/22/2018 - 20:07

I agree with what you are saying.  Another factor not mentioned is the level and abilities of students.  I have had students who have some really serious struggles with the simplest math.  There could be a student next to them who can do it without a problem.  I would like for them to do it the best way possible but I also have 20 other kids in the room and I have to pick and choose.  I have been pleasantly surprised lately that when I have given them some time to problem solve they do it in ways that surprise me....might be a future blog post here....