## Tuesday, October 1, 2019

Ahhh, the mole.  Ask students, "Which weighs more: a dozen pizzas or a dozen skyscrapers?" They will easily answer.  Ask students, "Which contains more items: a dozen pizzas or a dozen skyscrapers?" They will still answer easily.  Then you ask a question about the mole, and chemistry students are baffled.

The Goal

The goal in teaching the mole in a first year general chemistry course is two-fold:

First, students need enough of an understanding of what the mole is to be able to answer questions about the concept of the mole (similar to the ease with which they answer questions about the concept of a dozen).

Second, students need to be able to easily and efficiently use dimensional analysis to convert between grams, moles, and particles.  Setting the foundation well here will allow for a seamless, and much less painful, introduction to stoichiometry later in the course.

The Problems

In many years of teaching chemistry, I have noticed two main problems when teaching this unit.

First, while many students pick up on the pattern of dimensional analysis quite quickly and easily, others are completely confused by the idea of conversion factors.  I cannot count the number of times I have seen very creative, and very made up, conversion factors, like "1 atom = 58.44 mol" or "1 g = 6.02 x 1023 atoms."  When you have spent days in class practicing, and pointing out that there are only 2 conversion factors, and that these conversion factors mean something, seeing these random conversion factors pop up on tests and quizzes can be so frustrating.

The second problem with this unit is that some students will focus all their time and energy on solving math problems, without really having any true visual about the relationship between a mole, a particle, and mass.  When I ask a simple relational question, they spend too much time trying to set up a math problem instead of using common sense.  If I ask which has greater mass: 1 atom of carbon or 1 mole of carbon, the answer should be obvious.  But too many students feel overwhelmed by the unfamiliar vocabulary and are unable to simply think logically.

The Solution

 Students stay engaged and eager  to practice when you add competition to the lesson!
This year, I decided to try something new with this unit.  Although I teach at an international private school and have a lot of very strong students, I also have quite a few weaker students, especially in their math skills.

Every student in 10th grade takes Chemistry, no matter what math class they are in, which can lead to lots of anxiety and stress when we get to topics that are heavily math focused.
 Mole concept game -- thinking through relationships  without a calculator

I decided to make this a self-guided lesson.  I wanted students to first recognize the relationship between mass, number of items, and a quantity that is familiar to them -- the dozen.  I then wanted them to see how you can use dimensional analysis to perform conversions using those relationships.  Then, students could use those same skills to tackle the concept of the mole.

 Even lower level students  are excited to practice!

I had several worksheets available -- covering both the mole concept and mole conversion calculations.  I never collect homework - I want students to feel free to try, make mistakes, and learn from them without the stress of a failing grade - so I have the answer keys available for them to check as they go and to learn from their mistakes.

In the past, the only worksheets I had students complete are the mole conversion ones.  I usually go over the mole concept in class with check for understanding questions, but answering questions on a PowerPoint as an opening question or during a lesson is not nearly as challenging as completing a whole worksheet focused on this concept.  In previous years, the mole concept questions are some of the most missed questions on the end of unit test, so giving them additional practice seemed necessary.

The truth is -- this concept and math is not terribly difficult.  It is not any more difficult than understanding the meaning of a dozen (except with a few more zeros!).  Some students see the patterns immediately and fly through the problems and others need some time to work through it, staring at examples, and seeing connections.  Using self-paced guided notes takes a whole lot of preparation up front, but the payoff in the classroom is worth it.

 First set of scaffolding cards
For this one, I allowed students to work with a partner (assigned by me, based on ability), at their own pace.  Some flew through the packet and the worksheets, making the connections quite easily.  Some really struggled to follow the examples and see how dimensional analysis works.  By doing this self-paced lesson, and allowing stronger students to move right along when they understood,  I was able to work one-on-one with struggling students and see exactly where they had misunderstandings.  For those who just couldn't wrap their minds around conversion factors, I had scaffolding cards, to allow them to help build their dimensional analysis problems.
 Second set of scaffolding cards

After some practice with the first set of cards, I switched them to the second set, which included less information.

By the time the quiz came around, they were all much more familiar with how their dimensional analysis problems should look, and even weaker students were able to set up most of the problems unassisted.

In terms of understanding the mole concept, and the relationship between moles, particles, and mass, I created a game that allows students repetitive, competitive practice.  Playing the game (see photos above) allowed students practice in making fast, informed decisions about the relative sizes of masses and moles of these substances, without necessarily plugging numbers into a calculator.

The Results

Last year, about 15% of my first year chemistry students failed the mole conversion quiz. This year, only 1 student did.  The unit test included concept questions, and these were answered at a much higher passing rate than previous years.

And Now...

Mole Day is coming! I am excited for my students to participate in the Molympics (see #molympics on Twitter to join the fun too!) this year on October 23rd, and I am hopeful that they will be able to demonstrate a strong understanding of this concept.

There are so many fun ways that you could celebrate Mole Day with your students, without letting up on the rigor or high expectations of a chemistry course.  If you haven't yet introduced your students to the mole, you could spend the week with the lesson and game mentioned above (linked below).

If you've already learned about the mole and just want students to have extra practice with dimensional analysis, see my FREE "How Big is a Mole" project.

Everything mentioned in this blog post is available in the bundles below. Save yourself time and frustration in planning student-centered lessons to engage your students with this important topic!

 Mole Lesson Bundle --  Guided Lesson, Game,  Worksheets, Quiz
 Chemistry Calculation  and Mole Unit Bundle
 FREE Mole Project

What are you doing for Mole Day?  Share ideas and pictures on  My Science Toolbox!

Happy Mole-ing!