Composition Books to Packets

Hi friends! I took a little hiatus from writing to focus on what is happening in my classroom. Now that I have some free time, I wanted to share about some changes I made last year and some changes I want to make next year. Vacation is over and my mind is already on next school year!

Some of you who are AMTA members know I made a big switch from composition books to packets last year in my general chemistry classes. Here are the reasons that lead me to making that switch:

  1. Lost papers! I’m sure you all have that student whose organization system is one folder for all of his/her classes. Over the course of the year, that folder gets so jammed pack that it is actually just two folder halves making a paper sandwich. I have dug through many paper sandwiches for lost worksheets only to end up making extra copies.
  2. Messy, incomplete and lost composition books. I found that students have trouble keeping neat composition books with the information I think they need. This comes back to lack of modeling expectations on my part. I also do not give any formal, PowerPoint or guided notes so students often do not know what they should write down.
  3. The SBG thread needs to be pulled through everything. The thing that ties all of SBG together is the learning targets. I wanted a system that makes sure those learning targets are at the forefront of every activity.

Putting worksheets in a packet is easy but eliminating the composition book takes a lot more thought. I did not want to spoon feed my students everything but I also wanted them to be successful and gather the information they need in one place. I remembered seeing what Kelly O’Shea had come up with for her physics materials and that inspired what I came up with for chemistry.

I cannot post entire packets here because they include copyrighted AMTA materials but they are posted to the AMTA members site. I will be adding more this summer as I clean them up.

I will break down the anatomy of my packets that can be applied to any unit.

COVER PAGE: The cover page is where students write their learning targets and track their grades. This puts the learning targets at the forefront of the unit. Every time a student needs to write down a new learning target, they need to get out their packet.

LAB PAGES: Lab pages are the trickiest because you need to find a balance between guiding students without spoon-feeding them. It also helps to keep the formatting consistent so students know what to expect from a lab. I try to format it like a lab write-up: purpose, methods, data, discussion/conclusions. The only part that changes from lab to lab is the conclusions section. I like to put one or two questions at the end of each lab that sum up what I want students to take away.

WORKSHEET PAGES: Worksheet pages are the easiest. Just insert whatever worksheets you would hand out to students. Make sure to put the associated learning target(s) at the top though!

END PAGES: I end every packet with the same three pages: practicum, the model so far and additional notes. All of these blank pages are graph paper style like the lab pages. They provide students to write down practicum calculations, what we added to our model and anything else they don’t have room for. Since this is the first year I used packets, I found myself forgetting to put activities in so the additional notes pages ended up being a lifesaver!

These packets were great this past year! I only had to worry about making copies once a unit, students didn’t lose papers, learning targets actually got written down and I think students got more out of the lab activities. This coming school year my district is implementing a 1:1 Chromebook program. My summer project is figuring out how to make this system paperless! I think I will keep composition books for my honors students but my general chemistry and physical science students will be sticking with packets.

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Honors Chemistry Learning Targets

I just updated my general chemistry learning targets to this year’s edit and I thought I would post my honors chemistry targets as well. I picked up this prep for the first time this year so I’m sure these targets will undergo some serious edits throughout the year.

I also noticed that I switch from the language “learning goals” to “learning targets” from the last time I posted. This was due to an effort in my previous district to have everyone using the same language. I actually prefer the word “goals” for students but teachers seem to be more familiar with “targets.”

Unit 1: Physical Properties of Matter

1.1 – I can represent elements, compounds and molecules as “hard spheres” in particle models

1.2 – I can apply the Law of Conservation of Mass to situations involving chemical and physical change

1.3 – I can define mass, volume, and density in terms of a substance’s particles using appropriate units

1.4 – I can apply the relationship between mass, volume and density to solve quantitative problems
Unit 2: Energy and States of Matter Part 1

2.1 – I can represent the characteristics (motion, arrangement, and attraction) of particles in different states of matter

2.2 – I can relate the temperature of a substance to the average kinetic energy of its particles

2.3 – I can relate the pressure a gas exerts to the number of collisions its particles make with a surface

2.4 – I can determine the partial pressure of a particular gas in a mixture

2.5 – I can predict the effect of changing the pressure, volume, or temperature of a gas on other variables when two variables are held constant

2.6 – I can predict the effect of changing the pressure, volume, or temperature of a gas on other variables when one variable is held constant

Unit 3: Energy and States of Matter Part 2

3.1 – I can describe the energy transfer between a system and its surrounding during a phase or temperature change as endothermic or exothermic

3.2 – I can recognize that energy can be stored in an object or system as thermal energy or phase energy

3.3 – I can draw an energy bar graph to account for energy transfer and storage in all sorts of changes

3.4 – I can identify phases present and the various phase change temperatures for substances from a heating/cooling curve

3.5 – I can state the physical meaning of heat of fusion, heat of vaporization, and heat capacity

3.6 – I can calculate the quantity of energy transferred, mass of substance involved, or temperature change for a system that has undergone a temperature change

3.7 – I can calculate the quantity of energy transferred, mass of substance involved, or temperature change for a system that has undergone a phase change
Unit 4: Describing Substances

4.1 – I can distinguish among elements, compounds, pure substances, and mixtures

4.2 – I can distinguish between solutions, suspensions and colloids and describe the unique properties of each

4.3 – I can predict the effects of various factors on rates of dissolution

4.4 – I can determine how the boiling point and freezing points of a solution differ from those of a pure substance

4.5 – I can state features of Dalton’s model of the atom
Unit 5: Particles with Internal Structure

5.1 – I can explain how ions are formed and how they combine to form neutral substances

5.2 – I can determine the oxidation numbers for various elements in a compound

5.3 – I can distinguish between metals and nonmetals and describe the unique properties of each

5.4 – I can distinguish between ionic, molecular, and atomic solids and describe the unique properties of each

5.5 – I can name and write formulas for ionic compounds

5.6 – I can name and write formulas for molecular compounds

5.7 – I can determine whether a substance is ionic or molecular from the name or formula of a substance

Unit 6: Chemical Reactions: Particles and Energy

6.1 – I can identify evidence of chemical reactions in terms of macroscopic observations

6.2 – I can write balanced chemical equations including net ionic equations

6.3 – I can explain that coefficients in a chemical equation describe the quantities of substances involved and subscripts describe the number of atoms involved

6.4 – I can identify basic patterns in the way substances react (reaction types) and use them to predict products

6.5 – I can predict the solubility of products of a chemical reaction based on chemical properties

6.6 – I can describe endothermic and exothermic reactions in terms of storage or release of chemical potential energy

6.7 – I can calculate the enthalpy for a given chemical reaction using Hess’s Law

6.8 – I can use enthalpy, entropy and free energy to predict if a reaction will occur
Unit 7: Counting Particles Too Small to See

7.1 – I can convert between mass and moles of an element or compound

7.2 – I can convert between the number of particles and moles of an element or compound

7.3 – I can relate the molar concentration (molarity) of a solution to the number of moles and volume of the solution

7.4 – I can determine the empirical formula of a compound given the mass or percent composition

7.5 – I can determine the molecular formula of a compound given the mass or percent composition and molar mass

7.6 – I can calculate the rate of effusion for a gas
Unit 8: Stoichiometry

8.1 – I can calculate the number of moles of reactants and products in a chemical reaction from the number of moles of one reactant or product

8.2 – I can determine the theoretical yield for a reaction

8.3 – I can determine the percent yield for a reaction

8.4 – I can determine the limiting reactant in a chemical reaction

8.5 – I can use the ideal gas law equation to determine the number of moles in a sample of gas not at standard conditions
Unit 9: Oxidation- Reduction Reactions

9.1 – I can identify redox reactions as a type of chemical reaction

9.2 – I can assign oxidation numbers to elements in a redox reaction

9.3 – I can write oxidation and reduction half reactions

9.4 – I can balance redox equations
Unit 10: Acids and Bases
10.1 – I can distinguish between acids and bases and describe the ions they form

10.2 – I can write the balanced equation for a proton-transfer reaction

10.3 – I can define and calculate pH as the negative log concentration of hydronium ions in a solution

10.4 – I can write the names and formulas of common binary acids and oxyacids

10.5 – I can predict the products of a neutralization reaction between a strong acid and strong base

10.6 – I can distinguish between strong acids and bases and weak acids and bases

10.7 – I can write net ionic equations for reactions between strong acids/bases and weak acids/bases
Unit 11: The Nucleus

11.1 – I can draw the models of the atom proposed by Thomson and Rutherford.

11.2 – I can state the location in the atom, the charge, and the relative mass of protons and neutrons

11.3 – I can distinguish between the atomic number, mass number and atomic mass for an element

11.4 – I can calculate the average molar mass of an element using mass spectrometry data

11.5 – I can describe the three types of nuclear radiation in terms of mass, charge, penetrating power, ionization potential and biological hazard

11.6 – I can write a balanced equation for a nuclear decay reaction

11.7 – I can use the half-life equation to solve for the fraction of original material remaining,
elapsed time, or half-life

11.8 – I can analyze the pros and cons of nuclear technology including fission and fusion applications
Unit 12: Beyond the Nucleus

12.1 – I can draw the model of the atom proposed by Bohr

12.2 – I can represent the first 20 elements on the periodic table using men-in-well diagrams

12.3 – I can account for periodic trends in ionization energy, atomic radius and electronegativity

12.4 – I can represent the first 20 elements on the periodic table using electron configurations

12.5 – I can visualize the 3D molecular geometry of simple molecular compounds

12.6 – I can construct Lewis structures for simple molecular compounds

12.7 – I can determine whether a simple molecular compound is polar or non-polar

12.8 – I can identify the intermolecular attractions at work in a substance and their implications on material properties
Unit 13: Reaction Kinetics

13.1 – I can use collision theory to identify and explain factors that influence reaction rate

13.2 – I can explain the terms “activation energy” and “catalyst” and their relationship to reaction rates

13.3 – I can write the rate law for a simple reaction based on experimental data

13.4 – I can define equilibrium in terms of the reaction rates of a reversible reaction

13.5 – I can identify and explain factors that cause equilibrium to shift

Laboratory Skills

Lab.1 – I can conduct and clean up laboratory experiments properly and safely

Lab.2 – I can identify the hypothesis to be tested, phenomenon to be investigated, or the problem to be solved

Lab.3 – I can document experimental procedures clearly and completely

Lab.4 – I can record observations and experimental data neatly and accurately

Lab.5 – I can justify conclusions using experimental evidence
Communication Skills

Com.1 – I can communicate precision of measurements and calculations using significant figures

Com.2 – I can analyze the slope and y-intercept for a line of best fit to explain a scientific relationship.

Com.3 – I can convert between units of measurement

SBG Presentation

I have been doing a lot of presentations on standards-based grading lately and I thought this might be a good place to post the slides I have been using. Feel free to borrow, implement and ask questions!

PDF: HSTW-Making Standards-Based Grading Work for You

Chemistry, more like cheMYSTERY to me! – Stoichiometry

At this point in the year, the curriculum is getting more difficult and is building to what I call “the top of chemistry mountain.” I call stoichiometry the top of chemistry mountain because it pulls together the big picture of chemistry: chemical reactions, balanced equations, conservation of mass, moles and even gas laws! One of my students depicted the harrowing climb below:

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Let’s recap the climb from Unit 7 before we jump in:

  • Molar masses on the periodic table are relative to 12 g of Carbon-12 or 1 mole of carbon
  • There are 6.02 x 10^23 particles in a mole
  • Empirical formulas represent the simplest ratio in which elements combine and can be calculated using mole ratios
  • Molecular formulas represent the actual number of atoms of each element that occur in the smallest unit of a molecule. This may be the same as the empirical formula.

This unit is long so you might want to pack a snack!

I start Unit 8 with an activity my students always beg me for from the first time they use Bunsen burners: making s’mores. Of course, those s’mores cost them some chemistry!

S’mores Stoichiometry

S’more stoichiometry is a fun and easy activity to introduce students to the idea of reaction ratios and even limiting reactants. A s’more can be made with the balanced equation:

Gm2 + 2Ch + Mm –> Gm2Ch2Mm

Where Gm is the diatomic element graham cracker, Ch is chocolate and Mm is marshmallow. Students go through a series of calculations converting between mass of ingredients and number of ingredients (mass of reactant to moles of reactant) and then to quantity of s’mores (moles of reactant to moles of product). Students even complete a limiting reactant problem when given a finite amount of each ingredient. The reward for all this math? Delicious, gooey, Bunsen burner s’mores.

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Now that they have gotten the marshmallow roasting out of their systems, it is time to start the final ascent to the top of chemistry mountain!

BCA Tables

I love a lot of things about the Modeling Instruction curriculum, but BCA tables might be my favorite. If you are not familiar with BCA tables, check out the ChemEdX article I wrote here. BCA tables are an awesome way to help students think proportionally through stoichiometry problems instead of memorizing the mass-moles-moles-mass algorithm. I introduce BCA tables giving students moles of reactant or product. I add mass, percent yield, molarity, and gas volumes one by one as “add-ons” to the model.

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Percent Yield Lab

The first “add-ons” are theoretical yield and percent yield. Students react solutions of sodium carbonate and calcium chloride (mass and mixed by students) to form calcium carbonate. Students gravity filter (I do not have aspirators in my room for vacuum filtration) the precipitate and dry it. img_0504 (1)While waiting for the product to dry, students calculate their theoretical yields. This calculation requires students to realize they need to convert their masses of reactants to moles before using a BCA table and then convert the moles of product from the BCA  table to mass of product. After drying, students are able to calculate their percent yields and discuss why this is an important calculation and what their possible sources of error are.

Molarity

The next “add-on” to the BCA table is molarity. This can be saved for after limiting reactant, depending on how your schedule works out. Students learned about molarity back in Unit 7 but it never hurts to review before you jump into the stoichiometry. Again, the key to keeping this simple for students is molarity is only an add-on. Only moles can go in the BCA table so calculations with molarity should be done before or after the BCA table.

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Limiting Reactant PhET

Now that students are stoichiometry pros when given excess of one reactant, it is time to “adjust to reality” as the Modeling curriculum says. This year, I introduced the concept of limiting reactants with the “Reactants, Products and Leftovers” PhET. Students started by making sandwiches with a BCA table and then moved on to real reactions. This activity helped students visualize what it looks like to have left over product. The key to using the PhET is to connect every example to the BCA table model. Before switching from sandwiches to actual reactions, I have a quick whiteboard meeting to introduce the term “limiting reactant.”

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Limiting Reactant Practice

After the PhET, students work on the “Adjusting to Reality” worksheet from the Modeling Instruction curriculum. This worksheet starts by giving students reactant quantities in moles and then graduates them to mass values. The BCA table helps students easily pick out the limiting reactant and helps them see how much reactant is leftover and how much product is produced in one organized table.

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I then have students work on a worksheet I call “All the Stoichiometry” because it has all types of problems with all levels of difficulty to make sure students can discern when to use the different tools they have collected.

Chemistry Feelings Circle

When I have a really challenging problem that I think would take too long for individual groups to solve, I hold a chemistry feelings circle. I arrange all of my seats in a tight circle and place a pile of whiteboards and markers in the middle.

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Every student must sit in the circle and the class must solve the problem together by the end of the class period. I act like I am working on something else but really I am taking notes about their conversations. Once all students have signed off on the solution, they can elect delegates to present it to me. This year, I gave students a zombie apocalypse challenge problem involving the 2-step synthesis of putrescine. Students had to determine whether they could synthesize enough putrescine to disguise all of their classmates. Spoiler alert, there is not enough!

Ideal Gas Law

With limiting reactant under our their belts, it is time for another stoichiometry add-on, the last one. It is time for the ideal gas law. I return to gas laws through the molar volume of a gas lab. Students know how to convert mass and volume of solution to moles. What about gas volume (I may bump this back to the mole unit next year)? That question leads to the challenge of determining the volume of 1 mole of gas at STP. I usually use the traditional gas collection over water set-up but this year I was gifted a class set of LabQuest 2’s and I wanted to try them out. I used the Vernier “Molar Volume of a Gas” lab set-up instead.

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I am not sold on this procedure but it got us the data we needed. With the molar volume of gas at a STP, we can derive PV=nRT and calculate R (the universal gas constant).

Grab-bag Stoichiometry

At the top of chemistry mountain, I give students a grab bag of stoichiometry problems. They may have to convert reactant or product mass, solution volume/molarity or gas volume to/from moles in addition to completing a BCA table. I give students a flow chart to fill in to help them sort out the process.

Unit 8 Practicum

Once students reach the top of chemistry mountain, it is time for a practicum. I use Flinn’s micro-mole rocket activity for the practicum but I leave it very open ended. I show students that hydrogen gas reacts with oxygen gas to form water and this creates enough energy to power the rocket (pipet bulb). From there, I set them loose to figure out what volume of each gas they need and where to mark their rocket so they can fill the gas volumes correctly. I also have students do some fun (not the word my students might use to describe them) stoichiometry calculations (see below).

Stoichiometry Coding Challenge

I usually end a unit with the practicum but I really wanted to work a computer coding challenge into this unit. Asking students to generalize the math they have been doing for weeks proves to be a very difficult but rewarding task.

For the coding challenge, I ask students to write a series of cumulative programs in Python that build to a stoichiometry calculator. First, students write a simple code that converts between mass and moles.

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Then they write similar codes that convert between solution volume and moles and gas volume and moles. Students then combine those codes to create a calculator that converts any unit to moles. Once students have the front end of the stoichiometry calculator, they can add in coefficients. Finally, students build the back-end of the calculator, theoretical yield. You can read my ChemEdX blog post here.

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By the end of this unit, students are about ready to jump off chemistry mountain! Luckily, the rest of the year is a downhill ski.

Let’s see what we added to the model so far…

  • The coefficients in a balanced equation represent the molar ratios in which elements and compounds react
  • The theoretical yield for a reaction can be calculated using the reaction ratios
  • The percent yield for a reaction is based on the quantity of product actually produced compared to the quantity of product that should theoretically be produced.
  • The reactant that runs out first is called the limiting reactant because it determines how much product can be produced
  • The pressure, volume, temperature and moles of an ideal gas can be related through the universal gas constant

 

 

 

 

 

Chemistry, more like cheMYSTERY to me! – The Mole

We are just chugging along in chemistry this year. On to Unit 7! First let’s recap Unit 6:

  • Chemical reactions can be identified by a change in color, temperature or odor or the formation of a precipitate or a gas
  • Particles can rearrange during a chemical reaction but mass must be conserved (total number of particles does not change)
  • Chemical reactions occur in predictable patterns
  • It takes energy to break bonds and energy is released when bonds are formed
  • Exothermic reactions release heat when the chemical energy of the system is decreased. Endothermic reactions absorb heat when the chemical energy of the system is increased.

We have finally arrived at the mole! I know this ordering of units is a little strange but I have found that students do much better with stoichiometry if they are coming right off the mole unit.

Packing Peanut Challenge

The beginning of my mole unit is based on the concept of relative mass. I start by presenting students with this large bag of packing peanuts, a balance, and a small sample of packing peanuts and say “figure out how many packing peanuts are in here, you can’t open the bag.”

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It takes students a few minutes to formulate a plan but eventually they realize they need to use the mass of their sample of packing peanuts to set up a proportion. This establishes the idea that we can count by massing. This technique is really useful when you have a large amount of something or when you need to count things that are very small (in the case of atoms, both!).

Relative Mass Activity

The packing peanuts challenge leads nicely into a more in-depth relative mass activity. I adapted this relative mass activity from the Modeling Instruction materials because I didn’t have any hardware but I did have paperclips, metal shot and pennies. In the activity, students are given vials with the same number of the aforementioned objects in each vial.

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Students complete a series of calculations converting between mass and number of items. The activity ends with students calculating the relative masses of the items and comparing those relative masses to numbers on the periodic table. At this point, I make the connection that the atomic masses on the periodic table are all relative (first to hydrogen, now to carbon). Since scientists could not measure the mass of a single atom, a common sample size of particles was needed to compare masses of different elements: this is the mole. Right now, it does not matter how many particles are in a mole. All we need to know is the atomic mass on the periodic table is the mass of one mole of an element. Hence, we call this the molar mass.

I extend this discussion with a bean challenge. I give each group a vial of 50 white beans, a vial of 50 red beans, a vial with an unknown quantity of bean compounds (2 white beans and 1 red bean) and an empty vial. Students are given the challenge to determine how many bean compounds are in the mystery vial. This task requires students to find the mass of 2 white beans and 1 red bean (like finding the molar mass of a compound) and then set up a ratio to determine the number of bean compounds in the vial (like calculating the number of moles in a sample when given the mass). Students are generally able to then quickly make the connection between calculating the mass of a bean compound and calculating the molar mass of a chemical compound.

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After completing these two activities, students can very easily move to practicing mass/mole conversion calculations.

Once students have relative mass down, we can figure out exactly how big a mole is.

Size of Mole

I start the discussion about the size of a mole by asking students to measure out a mole of water. This takes a little bit on thinking initially but eventually students remember from Unit 1 that the density of water is 1 g/mL so 1 mole of water would be equal to about 18 mL of water.

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I then ask students “how many particles of water do you think make up that 18 mL by order of magnitude?” Students usually guess around the order of magnitude of one trillion to 1oo trillion. They are always very surprised to learn that they grossly underestimated. I follow up this discussion with some fun, size of a mole calculations to put that giant number in perspective. Did you know that a mole of basketballs would fit in a ball bag roughly the size of the Earth?

Students are then able to complete mole/particles conversion calculations and two-step conversion calculations. While students complete these calculations, I also have them working on the multi-day nail lab.

Nail Lab

I use the nail lab to introduce the concept of empirical formula. Students observe the reaction of an iron nail with copper (II) chloride, only they do not know which ion of copper was used. Students figure out how much copper was produced and how much chlorine was used, and then calculate the mole ratio and find the empirical formula. This lab takes 3 days (set-up, collect the precipitate, dry and measure the precipitate). Since each step does not take a whole class period, I do this in conjunction with mole/particle conversion calculations. I have also used the synthesis of magnesium oxide lab for determining an empirical formula which can be done in one class period (not counting the discussion).

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Empirical and Molecular Formulas

After the nail lab, I jump right into calculating empirical and molecular formulas. For next year, I think I will make a more distinct transition from empirical to molecular formulas as this year my students had some trouble delineating the two. I use hydrogen peroxide and glucose as my poster child examples for the difference between empirical and molecular formulas.

To practice with empirical and molecular formulas, I have students play a round of whiteboard speed dating (see Kelly O’Shea’s blog) with a crime scene problem. The FBI has analyzed a white powder and they need to know if it is Tylenol (like the suspect claims) or cocaine. Students analyze the data and decided what to report back to the FBI.

Additionally, I have students work on “The Strange Case of Mole Airlines.” This activity was originally published in the Journal of Chemical Education and can be easily found with a quick Google search. This activity provides a wealth of practice with empirical formulas and also gives students the chance to form some conspiracy theories! Next year, I hope to set up a whole crime scene for students analyze!

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Unit 7 Practicum

As will all units, I wrap up Unit 7 with a practicum. I had students calculate the formula of a hydrate. Students came up with the general lab procedure as a class (evaporate off the water and calculate the change in mass) and completed the experiment and calculations within their groups.

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The practicum puts a wrap on Unit 7! Let’s sum up what we added to the model so far…

  • Molar masses on the periodic table are relative to 12 g of Carbon-12 or 1 mole of carbon
  • There are 6.02 x 10^23 particles in a mole
  • Empirical formulas represent the simplest ratio in which elements combine and can be calculated using mole ratios
  • Molecular formulas represent the actual number of atoms of each element that occur in the smallest unit of a molecule. This may be the same as the empirical formula.

That unit sets us up well for what I call the top of chemistry mountain, stoichiometry!

Switching from Mercury to MolView

One of my favorite Modeling Instruction activities is the comparison of crystal structures to derive properties of ionic, molecular and atomic substances. The original instructions for this activity have you use the Mercury software from ​​​​The Cambridge Crystallographic Data Centre to visualize 3D crystal structures. The Mercury software is simple to use and makes it easy for students to make connections between properties like boiling and melting point and crystal structure.

The only problem with the Mercury software is it does not play nice with Chromebooks. If your school is anything like mine, you have a lot of Chromebooks. It makes sense, they are affordable, fast and durable. They just lack some of the computing power and operating system of a PC or Mac. Luckily, Chromebooks come with a ton of great apps meant for the classroom. One of these great apps is MolView. MolView is very similar to Mercury as it allows students to visualize crystal structures but it is not as intuitive to use. Here is a quick walkthrough to get you started:

Go to molview.org and get started!

Does your screen look like this? (maybe with a different compound)

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Good! Now find your search bar, type in “sodium chloride” but don’t press “Enter”! See that little arrow next to your search box? Click it to get a drop-down menu like this:

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Select “Crystallography Open Database.” That will give you some options like this:

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From what I have found, you can just click the first one and it will give you what you need. Now you should have a unit cell of sodium chloride. You can hold down your mouse clicker and drag over the structure to rotate the structure like this:

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Want a bigger crystal? We can do that. Click the “Model” drop-down menu and scroll to the bottom where you should see the options, “load 2x2x2 supercell” and “load 1x3x3 supercell.” Like this:

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Let’s try a “2x2x2 supercell.”

Sodium chloride.clipular (1)Look how pretty that is! Go ahead an repeat with any other molecular, ionic  or atomic substance. For some substances, like copper, you can just type in the name of the element, press “Enter” and the unit cell will pop up! If you try that and it doesn’t work, just search the crystallography database and it should be there.

If you are using the original Modeling Instruction worksheet, make sure to use the chemical name, not the common name of the compound when you search. Make sure for sugar, you search “sucrose” and for baking soda, use “sodium hydrogen carbonate.”

Good luck!

Chemistry, more like cheMYSTERY to me! – Chemical Reactions

We last left off in the mind-boggling Unit 5. Let’s spend some time in a little more straight forward unit: chemical reactions. Don’t worry, I didn’t forget about the mole! It is coming up in Unit 7.

Here is what we added to the model so far in Unit 5:

  • All atoms contain mobile, negatively charged particles called electrons whose charge is balanced by the positive (pudding) core of the atom. (Thomson’s Plum Pudding Model)
  • In metals, the positive core has a weaker attraction to the electrons so electrons can move more freely than in non-metals, allowing metals to conduct electricity.
  • Metals tend to lose electrons and become positively charged cations and non-metals tend to gain electrons and form negatively charged anions.
  • Ions are charged all over and attract ions of opposite charge from all directions. When ions of opposite charges are attracted to each other, they form ionic bonds. Ionic substances are bonded throughout and have high melting/boiling points.
  • When the electrons of two non-metal atoms are attracted to the other’s positive core, a covalent bond is formed. Molecular compounds are bonded within molecules but the molecules are only attracted to each other through intermolecular attractions. Molecular substances have lower melting/boiling points compared to ionic substances.
  • Molecules can be attracted to each other through induced dipole-dipole attractions and permanent dipole-dipole attractions.
  • Ionic compounds are named by writing the metal first and then dropping the ending of the non-metal and adding the suffix -ide.
  • Molecular compounds are named by using the prefixes -mono, -di, -tri, -tetra, etc. to denote how many atoms of each element are present in the compound. The first element only gets a prefix if there is more than 1. For the second element, you must drop the ending and add the suffix -ide.

Yes, that was a LARGE unit!

I kick off Unit 6 by blowing stuff up (because that’s what chemistry is, right?)

Chemical Reaction Demos

I think a unit on chemical reactions should start with some chemical reactions. Insert your favorite demos here. I like to use smashing thermite, the blue bottle, mossy zinc and hydrochloric acid and of course igniting hydrogen balloons from gas produced from the previous reaction.

I need to set up this demo in the future!

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I have students observe the reactions and tell me how they know a chemical reaction occurred. By the end of the class we have a good list of macroscopic observations that tell us a chemical reaction has happened.

I then use the Zn and HCl reaction to introduce what is happening at the particle level. I have students draw out the particle models of the skeleton equation and they can see that it does not follow the law of conservation of mass. That is a big chemistry faux pas! The only way to fix this is to add more HCl to the reaction. This tells us that 1 zinc atom reacts with 2 hydrochloric acid molecules to form one molecule of hydrogen gas and one compound of zinc chloride. That sets us up nicely for balancing equations.

Balancing Equations

For balancing equations, it all comes down to practice. I start my students with balancing skeleton equations and then I have them move on to constructing their own skeletons from word problems. I have every student start by drawing the particle models to balance equations. Some students graduate from this quickly while others are always stuck to it. I just encourage students to do whatever works from them and I always leave individual whiteboards (sheet protectors with a white piece of paper) out on my desks during this unit for students who need them.

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Never underestimate a student’s commitment to learning!

I try to break up the monotony of balancing equation worksheets with some games. Sometimes I do speed competitions (by volunteer only so students who aren’t super fast balancers don’t feel any extra pressure) or group games like board hockey.

Once students are comfortable with balancing equations, we can move on to classifying reactions.

Classifying Chemical Reactions

I start this new topic with a pretty standard chemical reactions types lab. Students complete a series of mini experiments that are representative of the different reaction types. I like to have 2 reactions for every reaction type. I give students the reaction type and skeleton equation for each reaction. Students must record their observations, balance the equations and draw the corresponding particle models for each reaction. In that aspect, there is some confirmation built into this lab but the goal is not predict products but to find patterns.

To whiteboard this lab, I have each group whiteboard a different reaction. We then talk through each reaction and find patterns in the similar reaction types. The key questions in whiteboard meeting are: “what is similar between the two reactions you saw of this type?” and “why do you think it is called insert reaction type here.“That helps us come up with a set of rules. The rules are far more meaningful to students when they come up with them themselves versus being given the patterns through notes.

After the lab, I have students classify the reactions on a worksheet that they already balanced the equations for and we whiteboard it the next day. After classifying chemical reactions, we move on to the last topic of the unit!

Energy and Chemical Reactions

This topic brings back an old favorite, the LOL chart! Before I introduce the new and improved LOLOL chart, I show students one of my favorite demos.

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Don’t worry, I use a test tube and a Swedish Fish but you get the idea. This is a very exothermic reaction so it gets the conversation about heat and reactions started. I have students balance and classify the equation and then I draw an LOLOL chart on the board. This is where I introduce Echemical, which was foreshadowed in Unit 3. I ask students where they think chemical energy comes from and they can easily tell you,”from chemical bonds.” This is where you need to address the big misconception that energy is stored in bonds. It takes energy to break bonds and energy is released when bonds are formedCollegeboard has a quick explanation of this misconception with some nice real-life examples like, “why is hydrogen such a good fuel source if it’s not storing lots of energy in its bonds?” You can also mention activation energy here and how some reactions need a bit of energy to get started but do not require a constant energy input to proceed (I like to use the example of burning magnesium ribbon).

After that discussion, I take the students observations about the gummy bear reaction and fill in the LOLOL chart accordingly.

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The Swedish Fish (sugar) starts off at room temperature. After the reaction, the products are very hot. That heat had to come from somewhere and it wasn’t from the surroundings. That means it must have come from within the system; enter Echemical. After a while, the products cool down but the reaction is over so the chemical energy stays the same. That heat leaves the system so the reaction is exothermic. The LOLOL chart tells us that more energy was released forming new product bonds than what was used to break the original reactant bonds.

This is a good time to show an endothermic demo as well. I like ammonium nitrate and water because I use ammonium chloride and barium hydroxide later on for the practicum.

I have students try to whiteboard the LOLOL chart for this reaction and then we have a quick board meeting. All that is left then is some practice… and a practicum!

Unit 6 Practicum

For the Unit 6 practicum, I try to bring in as many learning targets as possible. I give students 2 reactions to observe: magnesium ribbon and hydrochloric acid and ammonium chloride and barium hydroxide. Students must give the signs that a chemical reaction has occurred, write the balanced equation, draw the particle models, classify the reaction and draw the LOLOL chart representing the observed temperature change.

That is it for Unit 6! It is small but mighty! Let’s take a look at the model so far…

  • Chemical reactions can be identified by a change in color, temperature or odor or the formation of a precipitate or a gas
  • Particles can rearrange during a chemical reaction but mass must be conserved (total number of particles does not change)
  • Chemical reactions occur in predictable patterns
  • It takes energy to break bonds and energy is released when bonds are formed
  • Exothermic reactions release heat when the chemical energy of the system is decreased. Endothermic reactions absorb heat when the chemical energy of the system is increased.

Next up… THE MOLE!

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