Wednesday, February 10, 2016

Stoichiometry Application: ID of an unknown carbonate

Students reacting their unknown carbonate with HCl.
Here's a quick activity that uses stoichiometry to identify an unknown substance. I start the kids with either sodium carbonate or sodium bicarbonate (labeled substance A or B). The students measure out about 2 grams of their unknown substance and then record the exact mass of their reactant. Both substances react with hydrochloric acid to produce aqueous sodium chloride, carbon dioxide, and water. Here are the two chemical reactions:
Na2CO3 (s) + 2 HCl (aq) --> 2 NaCl (aq) + CO2 (g) + H2O (l)
OR
NaHCO3 (s)+ HCl (aq) --> NaCl (aq) + CO2 (g) + H2O (l)

You can see right away where this is going...  The mole ratio is either 1:1 for sodium bicarbonate to sodium chloride, or 1: 2 for sodium carbonate to sodium chloride. The students react their sample of the unknown carbonate with 3M hydrochloric acid in an evaporating dish, using a watch glass to minimize splattering as the carbon dioxide bubbles up. Once the reaction is done, they heat the reaction mixture over the Bunsen burner to drive off the water. Any excess acid is also driven off with a thorough heating in the burner. When the reaction mixture is completely dried out, the only thing left is the salt! 

Driving off the water over the Bunsen burner.
This year, I did not give the students any instructions for figuring out their identification, I only asked that they justify their answer with calculations and an explanation. To my delight, the lab teams came up with several different solutions to this stoichiometry problem. One group decided to calculate the predicted mass of NaCl based on the amount of starting material; running the calculation for each of the two possible carbonate reactants. Another group worked backwards from the mass of NaCl produced to determine the mass of the reactant required, and then they matched it up with the mass of the starting material in the data. Another group converted both the starting material and the salt into moles, and then used a modified ICE chart to compare the mole ratio. And yet another group used the formula M = m/n to calculate the molar mass of the substance from the experimental data, then they compared their answer to the molar masses of the two carbonates. I was so happy with my decision to leave the calculations section out the lab file because so much creative problem solving happened without even asking for it. 

When it's all dried, the only thing left is salt.
I'm not sure where this lab originated. I think that one of my colleagues used to do a version of this lab with his students. They used to react a given amount of a known carbonate with HCl and make a prediction about the mass of NaCl formed. This was a good activity to practice stoichiometry calculations, but it seemed a little flat. Adding in the unknown carbonate component elevated this activity to a "real" problem to solve using the mole ratio concept. The experiment gives very good results and it takes about one hour from start to finish, including calculations.

Here are some of my students calculations and explanations:


This group first used the mass of the reactant and the product to calculate moles.


Next they calculated the mole ratio of reactant to product for both of the possible substances to find the match.

This group started with the mass of NaCl and worked back to the mass of the reactant.

This group made good use of the equation M = m/n to determine the identify of their unknown.




Sunday, December 6, 2015

NEACT Spectroscopy Day!

Spectroscopy Day at the NEACT Meeting at Pomfret School, December 5th 2015
Who doesn't love spectroscopy? Today I got to share one of my favorite lab projects with fellow chemistry teachers at the regional NEACT meeting at Pomfret School. The theme for the day was "Spectroscopy and Astronomy in the High School Classroom". Twelve teachers from MA, CT, and RI gathered together for the morning of hands on experimentation and lively discussion about spectroscopy applications. 

Sandy tapes her pizza box closed to remove light noise
During the first half of the meeting, all the participants built their own spectroscope from a pizza box. Yes, you can make a spectroscope from a pizza box that gives excellent quantitative data. This hands-on project takes atomic spectra beyond observations of pretty colors. Students can use their spectroscopes to identify unknown elements or analyze mixtures of elements by measuring the wavelength of the the visible lines.
Pedro and Calin cutting out the holes from their pizza boxes.

I led the teachers through the project in the same way that I do this lab with my students. They traced the template onto their own pizza box, cut out the necessary holes, and assembled the boxes. Once the boxes were built, they calibrated them with the mercury lamp. 
Josh checking the light leaking into his box, and Steve folding up the pizza box (not as easy as it looks).
Mike and Helaine are putting the finishing touches on their spectroscopes

Tim Rose, my colleague at Pomfret School, came out to help with the spectroscope project.


After we finished working with our spectroscopes, we took some time to discuss the project and possible road blocks to completing the project with their students. The razor blades were the first thing that many of the teachers raised as a road block. One of the teachers used two pieces of tape to make a slit for the light on his box, another teacher suggested using old gift cards to create the clean edge for the light slit. The second road block that several teachers brought up was access to atomic spectrum lamps. Many of the teachers don't have access to the gas tubes and lamps to calibrate the spectroscopes. One teacher suggested using colored LEDs with known wavelengths to calibrate the boxes. There was some question about using the mercury gas tubes in schools. Most schools have banned all mercury in the science labs, even a mercury emission tube with a tiny amount of it enclosed in glass. Some schools still use fluorescent lights with mercury, these make a good light source for the calibration. Another teacher shared a plastic version of the gas tubes that she has in her lab that is less likely to break. I enjoyed taking time to discuss the project with experienced chemistry teachers from a wide range of schools. 
Front row: (left to right) Pedro, Mary, Sandy, Jim, Steve, Kevin, Leslie, Tim
Second row: (left to right) Calin, Mike, Micaela, Ed, Sharon, Helaine

The second half of the program was dedicated to the connection between astronomy and chemistry. Josh Lake, our astronomy teacher here at Pomfret School, gave a talk about the development of spectroscopy in relation to discoveries in astronomy. Josh walked us through the use of spectroscopy in astronomy, highlighting the major developments and main players in the progression. A lively discussion accompanied his talk, with teachers asking and answering questions along the way.
Josh Lake talking about the uses of spectroscopy in astronomy.

We finished the program with a tour of the Pomfret School observatory. Josh drove the group in one of our short buses (know as "toasters" on campus) to the observatory for a quick look at our facility. We enjoyed lunch together in the dining hall to wrap up the day.
Josh is explaining the difference between emission and adsorption spectra.

Josh leading a lively discussion with the group about spectroscopy applications in astronomy.
Here are links that Josh shared with the group from his presentation:

Link to PPT Show (58 MB is the compressed size, it was 250 MB originally!): 





Hubble Ultra Deep Field Video: https://www.youtube.com/watch?v=oAVjF_7ensg

Friday, November 6, 2015

Nitric Acid Acts Upon Copper

The beautiful blue copper(II) solution is a great contrast to the brown nitrogen dioxide gas.
"Nitric acid acts upon copper," what does that really mean? In this fabulous demonstration, my students got to see it first hand. I brought out the fancy 2 liter round bottom flask to give this beautiful chemical reaction the extra flare it deserves. (Flinn Scientific, ChemFax Publication No. 91624)
 
The reaction starts right away when the nitric acid touches the penny.
The reaction set up: round bottom flask, tubing, basic solution.
The demonstration starts with a pre-1982 penny, freshly shined by one of my students. These old pennies are mostly copper, unlike the newer pennies that are actually copper-plated zinc. The shiny penny goes into the round bottom flask. I connected the flask to a 500-mL graduated cylinder filled with a slightly basic solution. The reaction starts with the addition of twenty milliliters of concentrated nitric acid into the flask. The brown gas, nitrogen dioxide, is produced immediately; with a vigorous bubbling and frothing. The brown gas spits and bubbles while a beautiful green liquid pools in the bottom of the flask. The gas begins to bubble through the pink solution, and eventually the pink color fades. The nitrogen dioxide reacts with the water to produce nitric acid in the cylinder, which drops the pH of the solution in the cylinder to turn the phenolphthalein indicator to colorless. When the reaction stops, the bubbling ends and the water slowly begins to creep back up the tube. Once the water drops into the flask, the temperature drops dramatically and then the water drains quickly from the cylinder into the flask. The big finale happens when the water gets sucked back into the round bottom flask and makes a loud slurping sound.
The round bottom flask filled with nitrogen dioxide.
I haven't done this demo for several years. I'm not sure why it fell off my radar, but it is one of my favorites. The truth is, I thought that it was too much set up and took too long to do this demonstration. I pulled it out of the "closet" because my students saw it in one of my homework videos and asked for it specifically. With their inspiration, I realized that this demo is the perfect fit for my new block schedule. With the longer classes, I can really enjoy this demo from the apparatus set-up to the final slerp of the water out of the graduated cylinder.

You can see the color change in the graduated cylinder here.

My student photographer took a shot from beneath the flask. So cool.

This reaction has it all: color change, brown gas, blue solution, heat exchange, and gas laws.





Friday, September 25, 2015

Scenes from the Hood

I love taking pictures of my students working in the lab. I can't help myself. When the kids are really getting into an experiment I want to capture it. As soon as they start to work, I pull out my phone. This week I started a new series I'm calling "Scenes from the Hood". I decided to try to take pictures of my students doing lab work from the inside of the fume hood. I've had the hood in my room for only one year. It still feels like such a luxury item. The novelty has definitely not worn off yet. Why is ventilation a luxury item, you ask... Don't get me started! Let's just celebrate the fact that now I have it and I can do more interesting chemistry with my students because of it.

Ventilation in the chemistry lab is an important part of a safe environment. Keeping the air clear is a matter of personal care for a chemistry teacher and the students. As a teacher, I am in the lab at least 6 hours a day, compared to my students 80-minutes. I am so happy to have a safer work environment with proper ventilation in the lab. Anyone who doesn't have good ventilation, you can go to Flinn's safety training for a short video about the importance of ventilation that you can use to support your case with administrators.

This week my Chemistry Honors students did the Pomfret School classic: The Iron and Sulfur lab. It's an awesome start to our lab work because of the flames, the smells, the breaking of the glass test tube, hydrochloric acid, heating with the Bunsen burner, and iron filings/magnets. I can't think of any other lab that "has it all" like this one. Add to that the fact that they are all scared to do anything because of the lab safety talk, and you have a pretty memorable experience for the kids.

Here are my "Scenes from the Hood" shots for the week.
These two are watching the bubbles in the gas producing reactions of Fe and FeS with HCl.

Wafting the gas to observe the smell (rotten eggs comes to mind).

These girls are looking into the fume hood for inspiration.

I love the photos my students include in their lab reports, not to mention the ones that end up on Instagram and Facebook.


And what about all the other fun pics I took? Here are a few photos of my new students investigating the chemical and physical properties of iron and sulfur.

The nicest looking iron sulfide pellet of the week! 

Look at the glow of this chemical reaction.

And then the plunge into cold water to shatter the test tube. Awesome.


Sunday, September 20, 2015

Highlights from Week One


Here are some scenes from my first week of school for 2015-2016. Selfies are a required part of Day One for each of my classes, along with a warning that they will all make the blog throughout the year.
Two of my AP chemistry students who are happy to identify the ions in their solution.
My AP chemistry class started off with the study of precipitation reactions. I thought this was a nice place to start to get them back into the practice of writing chemical formulas and balanced equations. They worked through their first POGIL from my new AP chemistry book from Flinn on net ionic equations. The week ended with a qualitative analysis experiment to identify ions in a solution. 



Rock band? No, my D-Block chemistry class with Tim Rose my co-teacher (the one with the beard).
In my Honors class, we started with some "real world" chemistry. I opened the week with a ChemMatters "Open for Discussion" article about caffeine. As part of the group discussion, I asked the students to propose an experiment to determine the amount of caffeine a type of food. I designed this question with a specific answer in mind. To my surprise and delight, the student in my class came up with a wide range of ideas for quantifying the amount of caffeine in a drink. I was reminded that prior knowledge is a valuable part of the learning process.
Two kids working together to write their first lab report in class using a shared Google Doc.

A serial dilution of food coloring, an analogy for the concentration of a contaminant in drinking water.
Another part of the week's homework was a reading about toxicity. I wanted to start off the year with a different perspective of the substances they encounter. LD-50 ratings of everyday substances, like water, make for an interesting calculations. It takes about 9 liters of water to kill the average 10th grader.

My AP Chemistry kids sporting our new goggles that I won at ChemEd.

F-Block chemistry is all smiles.
On a personal note, my oldest son started 9th grade this year at Pomfret School. After a long wait, he finally started classes this week. He had a good first week with his classes, but the highlight for him was the Outdoor Adventure team.
My baby boy starting high school this week at Pomfret School.
My husband and I work together at the school.  Brian is the AP and Honors physics teacher, making us one fourth of the science department here. Even though we work in the same department, he teaches in another building which prevents our paths from crossing much during the class day. Many of our students have us in back-to-back years in their science classes, and a few lucky kids have both of us in the same year. 
My husband and I make up 1/4th of the science department at Pomfret School! Day One was a family event.







Wednesday, August 26, 2015

NEACT 76th Summer Conference


Members of the NEACT Executive Committee
Mel Govindan opens the day with a warm welcome.
The NEACT 76th Summer Conference was a fun and action-packed one day event at Clark University.  The day started with a welcome from Mel Govindan, the NEACT President, for the approximately seventy participants. He enthusiastically greeted the new faces in the crowd along with many long-time members of the group.  Prof. Nancy Budwig, the Associate Provost and Dean of Research for Clark University, also welcomed us to her beautiful campus.  Clark provided us with a great location for our one-day workshop with lecture halls, classrooms, lab space, and a banquet for dinner.

Prof. Nancy Budwig from Clark University made us all feel right at home.
Mary Christian-Madden introducing Sr. Mary Virginia Orna
Sr. Mary Virginia Orna entertaining the crowd with her scientific story telling.
Our first speaker of the day was Sr. Mary Virginia Orna from the College of New Rochelle. Sr. Orna has an impressive list of publications and accomplishments in chemistry the include non-profit organizations, government service, industry, and of course teaching.  She entertained us with her unique style of story telling that blends together historical events, scientific discoveries, and the people behind the chemistry.  Her first talk was titled "Historic Mineral Pigments: Colorful Benchmarks of Ancient Civilizations".  Sr. Orna took us on a journey through time, looking through the lens of pigments.  She painted a colorful picture of how ancient civilizations around the world incorporated pigments into artwork.  The lecture had a feel of a wonderful travel log, as she shared her experiences traveling around the world to see the ancient artwork first hand.  Our group was captivated by her breadth of knowledge and deep understanding of the chemistry behind the enduring pigments from ancient artists. You can read about her study of pigments and color in her book The Chemical History of Color (a few lucky folks got to take home a signed copy of her book as a door prize!).











After our morning in the lecture hall with the whole group, we split into smaller groups for three rounds of concurrent sessions.  The offerings included technology applications in the chemistry classroom, lab activities, research talks, lab safety, and a trip to the local art museum.  The choices for the day provided topics of interest for participants from a wide range of teaching environments. I chose to attend one classroom strategy workshop, the safety talk, and one lab workshop.  Sr. Orna offered to give another talk about the "Undiscovered Elements" of the periodic table, based on her book The Lost Elements.

You can read the descriptions of the concurrent sessions on this google doc: Short Program Descriptions.
A group of teachers working together to computer simulations from Concord Consortium.

Daniel Damelin from Concord Consortium led a workshop on using modeling in the chemistry classroom

Dr. Jim Kaufman presented an excellent talk about lab safety.

Participants are experimenting with redox reactions that produce color changes with different indicators.

Dr. Mathangi Krishnamurthy from Fitchburg State University led a lab program.


The group gathered for the annual NEACT banquet, where we were treated to an Italian themed meal. We all enjoyed time to discuss the workshops from the day and to get to know our fellow chemistry teachers over a relaxed meal. At the banquet, Kathy Siok was awarded the John J. Swistak Award. This award was in recognition of Kathy's work behind the scenes for the summer conference every year, along with her many years of service to NEACT in a wide range of roles. It was a pleasure to join in thanking Kathy for all of her dedication our group.
Kathy Siok was the recipient of the John J. Swistak Award for 2015 in honor of her years of service in NEACT.
The day ended on a high note with one more talk from Sr. Orna titled "Fashion, Pharmaceuticals, Food and Fun: the Chemical History of Color". This talk was the perfect complement to the morning talk about pigments. Her creative discussion about the application of color in modern culture gave us a new perspective on the objects around us. Once again, her fluency with both the chemistry and history, punctuated by her research excursions, made this an inspiring ending to a wonderful day.

Now it's time to look ahead to next summer! The 77th NEACT Summer Conference will be going back to the usual four-day format. Plans are already in place for an exciting conference at the Massachusetts College of Liberal Arts in North Adams, Mass. The theme for the conference is "Chemistry, Naturally". Look for more information for presenters and participants on the NEACT website. Here's a link to the flier for Summer 2016. I hope to see you there!