Introduction to the Mole (Day 2)

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Objective

TSWBAT create a counting unit that can be used to relate mass and number of particles in a substance.

Big Idea

Students use popcorn kernels to develop a relationship between a counting unit (such as the mole), mass and # of particles.

Introduction

This lesson contains an activity that’s derived and modified from the Virginia Department of Education:  Science Enhanced Scope and Sequence – Chemistry.

This is day 2 of the first lesson of the unit where students begin to see there are different ways to measure and quantify objects.  This lesson has student measure a quantity of unpopped popcorn and use their data to develop an imaginary unit that will be similar to other counting units such as a dozen=12, a gross=144 or a mole=6.02 x 1023 atoms.

Day 1 students completed parts 1 and 2 where they developed an understanding that there units of measurements, such as a PCU, that can be use to quantify how many of something there is present.  They also established through the use of an imaginary unit called a PCU (popcorn counting unit) that the same number of objects can and will probably have different masses.  For example, one PCU of kidney beans did not weigh the same as 1 PCU of navy beans.

If students approach the mole both conceptually through inquiry, and mathematically, they will be more able to use the mole  to solve chemistry problems.  The idea is to develop a solid conceptual and analytical understanding of the mole.

Previous knowledge and skills needed for this activity:

  • Ability to measure mass using a scale
  • Atomic mass understanding
  • Factor labeling and scientific notation

Performance Expectation (PE)/Disciplinary Core Idea (DCI)

This lesson is aligned with HS-PS1-7, the uses of mathematical representations to support the claim that atoms, and therefore mass, are conserved during a chemical reaction; and DCI-PS1.B, the fact that atoms are conserved, together with knowledge of the chemical properties of the elements involved, can be used to describe and predict chemical reactions. Students develop an understanding of the mole as a basic counting unit in chemistry used to keep track of the amount of atoms present in matter.

Science and Engineering Practices (SP)

HS-PS1-7 is one of the few high school Performance Expectations with the primary focus on the use of mathematics to describe a concept.  Mathematical and computational thinking at the 9–12 level builds on K–8 and progresses using algebraic thinking and analysis.  Through their computational thinking, students will develop a way of counting various material that can be used as a parallel to help understand the mole as counting unit for the atom. 

 

Explore

20 minutes

As students walk into class I instruct them to take out their activity from previous day.  I give a quick review of the activity and what needs to be completed over the next 20 minutes

  • Beans, popcorn and scales are at the front
  • Parts 1 & 2 will all questions and boxes filled in.
  • Question 6 (data table 1) needs to completed
  • Class data (from question 8) is on the board, this can be used to answer questions 9-11.
  • data table 2 (part 2) calculations come from using 1 PCU in comparison to different types of beans.
  • Part 3 is a summary of what was learned in this activity.  Answer the following questions on the large white boards: 
  1. This should include information from both part 1 and 2, but should not be exact information that is directly copied from the activity.
  2. Your goal is to analyze what you leaned and provide an explanation of how a counting unit, mass and number of particles are related.  Do your best to relate this to chemistry.
  3. Provide an explanation or example how counting units are a useful tool in everyday life and science.
  4. Use the provided space to summarize your thoughts before writing on the board. 
  5. When creating your summary, use bullet points and diagrams (pictures) when possible.

As students are working on this I am making sure that the information in data table two is accurate. (Student work) I find that some students want to switch the data in column 2 with column 3.  For example they want to put the mass as the number of particles. This takes a little explaining to fix.  I use a dozen doughnut vs a dozen popcorn kernels.  I ask them how many in each, they respond 12.  I then ask which weighs more, they say the doughnuts.   Then I ask how many in one PCU of pinto beans, 63. How much does it weigh, 23.2 g.  

This usually corrects any confusion and I can move to the next group.

 


  

 

 

Explain

25 minutes

After all groups have completed part 1, 2 and 3, the popcorn lab (PCU key) is concluded with groups presenting what they have learned about counting units.  The goal of the activity is for students to develop an understanding of a counting unit and relative masses as a foundation for understanding the mole (student work).  At this point in the lesson the have been introduced to the mole, but have a very limited understanding of its relationship to Avogadro’s number and chemistry counting unit.  This activity is the first of several that slowly build an understanding of the mole, molar mass, # of particles in a substance and the conservation of mass in chemical reactions.

With 10 minutes left each group will have 1-2 minute to discuss what they learned.  Each group will take their white board to the front of the class and share with the class.  If time permits, other groups will have the chance to make comments.  Since there are 10-14 groups, comments will be very brief. 

The purpose of the presentation is for me to get a quick, informal assessment of what each group learned from the activity.  In addition it provides students with a deeper explanation of what they explored.  I believe the process of students seeing and learning what other students have learned is a valuable learning tool that is an important part of inquiry.  This type of learning can be used to build a more authentic understanding of difficult content, such as the mole. 

As students are presenting, I don’t say much because this is only an introduction to counting and the mole.

Here are a couple of example presentations that show a good introductory understanding to the mole. 

Evaluate

The evaluation portion of the lesson is mixed in with the explain portion of the lesson.  As students are presenting their white boards I am assessing whether or not students understand that counting units can be a useful tool in determining mass and number of particles.  

To assess this portion of the lesson I simply write on a roster sheet a plus, check or minus.  

 Plus (Plus example) = understand how to use counting units to calculate mass and particles and that not all objects have the same mass using a counting unit.

check (Check example) = understand that how to use a counting unit to calculate mass and particles, but do not understand that not all objects have the same mass using a counting unit.  Such as dozen donuts do not have the same mass as 1 dozen peas

Minus (minus example) = Do not understand counting units can be used to calculate mass and particles

 

This a very complex lesson that required students to apply critical thinking skills and work through a series of complex computations.  In this lesson they needed the ability to synthesize information and see the bigger picture that science uses counting units to show number of objects present and the mass.  In this particular lesson students needed to understand that a PCU would always be the same number of objects (equivalent to Avogadro's number and the mole) but depending on the substance (type of bean) the mass would be different.  

The objective of this lesson(s) was clearly met as illustrated in the student work examples.  Most students received a plus showing that they could do the calculations and scaffold the concept of the PCU to mole as counting unit.