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Honors Chemistry 27- Equilibrium

While looking for labs to go with Chapter 18: Equilibrium in Modern Chemistry, I had a hard time finding one for which I had the required ingredients.  The Modern Chemistry curriculum had this lab, Strike a Balance, which has the students come up with their own experiment to determine if your body is getting rid of excess carbon dioxide (produced by exercising) in your breath.  One of the students knew that carbon dioxide added to water would make it slightly acidic. So we could use a pH indicator in water to see when the carbon dioxide concentration goes up or down.  I had a couple of different pH indicators out and let the students decide which one to use.  I also had out a 0.1 M solution of NaOH to make the water slighly basic before they blew into it which would then neutralize it.  This could be useful depending on the indicator they chose to use.IMG_4345

In the photo above you can see a flask of tap water (roughly 100 ml) with a few drops of Bromothymol Blue indicator.  Note the pipette in the beaker with the indicator, this helps to make sure we don’t cross contaminate with the pipettes and protects my counter.  An interesting thing we found is that using distilled or filtered water makes a big difference. One group used filtered water and found the Bromothymol Blue indicator turned the water yellow, showing it was acidic, so they couldn’t get it to change color by blowing since that just makes it more acidic. So tap water works best for this experiment.

Students did different experiments, some timed how long they had to blow into the flask to change the color of the indicator after just sitting around, and then did it again after 5 or 10 minutes of exercise.  Some tried walking, then running, some did kempo (martial arts) forms, and some tried holding their breath.  Most found that after excercising they had to blow for a shorter time before the indicator changed color, indicating a higher concentration of carbon dioxide in their breath. FullSizeRender 7 The one anomaly was a student who is an Irish dancer and  therefore used to a lot of exercise.  The concentration of carbon dioxide in her breath didn’t seem to change after she exercised but she didn’t really get her heart rate up either.  I think we would have had to make her dance for quite awhile to see a change.

I found this other lab write up on the Royal Society of Chemistry‘s website which explained the chemistry in a bit more detail and with specific procedures which helped me as the teacher figure out how to do this and make it work with the indicators that I had.

Before class students were to watch Crash Course Chemistry 28: Equilibrium.  

But while preparing for class I found these videos which are also useful for this topic.

I also found this website , Chemistry LibreTexts, which has a lot of nice examples for calculating equilibrium constants, particularly when dealing with liquids and solids.

 

Intro Chem 24 – Game day!

IMG_9427Half my students were absent today so we had a game day (state testing…blah).  We played periodic table battleship, built molecules with snatoms and one of the students brought  Dr. Eureka Speed Logic Game. Battleship is easy to set up and you can find it all over the web.  I liked this handout from the Tech Museum.  I used a periodic table  from  sciencenotes.org because I wanted a bit of color but not too much information.  The kids called out various information, atomic number, symbol, element name or period and group numbers.  The only thing we did different than the handout was the kids drew their own battleships on the top table since it was harder for their opponent to see and it was easier to mark off their misses and hits on the bottom table.

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I really like the microsnatoms kit but it doesn’t come with any instructions for building molecules so I searched the web and found this nice worksheet above (its in the middle of this file Atoms and Molecules – Micron).  I also used a few pages from this file, Molecule Building! for vinegar (below) and sugar molecules.  The periodic table battleship was a big hit and I’m going to keep those handy for future classes.

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Honors Chemistry 26 – Boron Detection

IMG_9367This is another lab from the homescientist kit manual CK01A, Session XIII-1: Determine Boron Concentration with Curcumin.  This is an applied chemistry lab because we took soil and water samples from around the yard to test for the presence of boron.  Boron is used in some pesticides and if the concentration in the soil gets too high it can hinder plant growth.  This lab didn’t work quite the way it was supposed to.  The first part of the lab has you fill four wells in a 24 well reaction plate.  One well contains just distilled water, one well has just water plus HCl, one has sodium borate plus water and finally one has sodium borate, HCl and water.  Then a drop of tumeric reagent (included in the homescientist kit) was placed in each well.  All the wells turned yellow except for the one with the sodium borate with water which turned orange.IMG_9365

I’m not sure what the purpose of the HCl was, except maybe to show that this test doesn’t work with acids? Later in the lab the  manual says to add HCl to the test samples, but we just showed that would negate the results so we were a bit confused.  So when testing samples we did added the tumeric reagent, noted the color change and then added the HCl to see how it affected the results, and it turned most samples to the negative result (yellow).

Part two of the lab is making a reference matrix around a sample well in the middle, initially containing just distilled water.  The procedure for filling the wells is in the lab manual.  Now this does not look like it should.  You would expect the 1000ppm to be the darkest color with it getting lighter in color as you go clockwise around the sample.  All four groups had similar results even when adding more turmeric to make the colors darker.  We continued with the lab figuring we could at at least conclude whether or not the samples contained boron even if we couldn’t comment on the concentration.IMG_9371

Part 3 of the lab involves taking small samples of soil from outside (or a house plant), or water samples.  I also had some borax, which should definitely test positive for boron so we used it and a pesticide I found in the garage.  The students determined there was boron in Borax (it was the darkest color by far), the pesticide and water from our small pond (it was pretty weak but definitely more orange than yellow).  So while we couldn’t really comment on the concentration of boron in the samples we were able to conclude whether boron was present or not.IMG_9375

One thing I like to do with the chemicals is put each bottle in a beaker so the students can put the pipette in the beaker so everyone uses the same pipette with each chemical. This keeps us from going through a whole bag of pipettes and keeps the chemical from being knocked over, or dripping on my counter.IMG_9364

So this lab worked to some extent. Still not sure why the instructions said to add HCl to all the samples since that negated all the results.  I did find a video of the author of the lab demonstrating this lab but only for part two of the lab.

Students were to watch Crash Course Chemistry #28 Equilibrium before classs since we’re on the chapter about equilibrium in the textbook.

Being Pi Day, one of my students jumped in her car and rushed to the grocery store to provide Pi at the end of class.  IMG_9383

 

Intro Chem 23 – Catalysts

Before we started with the experiment I showed these videos from youtube.

and this video from a class room in Greece.

Quite a few of these demonstrations made use of catalysts to speed up chemical reactions. The lab, Chapter 6, Lesson 5: A Catalyst and the Rate of Reaction in the American Chemical Society’s middle school curriculum starts by asking students how they knew chemical reactions were taking place (there are links to two videos in the actual curriculum) in demonstrations they were shown.  Most of the kids immediately answered ‘bubbles’ or ‘gas was made’.    The two demonstrations  shown both involve the break down of hydrogen peroxide into water and oxygen.  Hydrogen peroxide will break down all by itself but its a fairly slow reaction so adding a catalyst can speed this up considerably.  I used snatoms to basically act out how a catalyst (Platinum) help break carbon monoxide and oxygen up so it can form carbon dioxide – check out this page for a great graphic showing this reaction. With the snatoms I could put the molecules on a white board and move them around and at the end show the catalyst atoms didn’t move or change so we leave them out of the chemical equations.

For the lab, the kids put 10 ml of hydrogen peroxide (3 percent like you can buy at the grocery or drug store) into a graduated cylinder, then 1 drop of dish detergent solution (to help make bubbles).  Nothing really happens at this point  but they should stop to notice that fact before they put a small amount (1/4 to 1/2 tsp) of yeast into the cylinder.  They swirl the cylinder a bit to help mix ingredients and then watch the bubbles form.  There are questions to answer on the lab handout – how do you know a chemical reaction was taking place?  what was used a catalyst? etc.IMG_9325

The second part of the lab used copper II sulfate solution to react with aluminum foil.  Usually this would be a very slow process because of an oxide layer on the foil, but once they put a small amount of table salt in the beaker, the reaction becomes quite vigorous.  The salt helps to destroy the oxide layer so the copper sulfate can reach the aluminum more readily.  Very quickly the foil turns a copper color  (photo below right) and then a few minutes later it disintegrates.  The cup also got very warm (almost 50 Celsius).

These were both pretty quick experiments so we had some time left over to make elephant toothpaste.

 

Honors Chemistry 25 – Reaction Rates

 

Today’s lab is from the homescientist chemistry kit manual, CK01A, determining the effect of temperature, concentration and surface area on reaction rates.  Its very similar to the lab I did yesterday with the middle school kids, but uses sodium bicarbonate tablets and vinegar. The chemistry kit didn’t come with enough tablets for 4 groups to do this experiment so I bought some off amazon.

Students started with 25ml of chilled (left in fridge over night) vinegar at 13 C and timed how long it took for a sodium bicarbonate tablet to completely react with the vinegar, detemined by the lack of bubbles/fizzing sounds.  They then used room temperature vinegar and repeated the experiment.  To get higher temperatures the beaker with vinegar was placed in the microwave for 5 seconds which raised the temperature about 10 degrees Celsius.  Students found that increasing the temperature reduced the reaction time considerably.

IMG_9153To test the effect of concentration students added 25 ml to their beaker and then added different amounts of water.  They were supposed to do 100%, 50%, 25% and 12.5% vinegar solutions but at least for two groups the 50% was still reacting after 25 minutes!  You can see in the photo above it wasn’t very rigorous but with a flashlight shining on the solution you can definitely tell the reaction was still taking place. This makes sense because even though you have the same number of sodium bicarbonate and vinegar molecules in the beaker, adding more and more water molecules makes it less likely for the vinegar molecules to bump into a sodium bicarbonate molecule… water molecules keep getting in the way.  Since this took so long we skipped the next two and moved on to surface area.

For surface area students dropped in a whole tablet, a tablet cut into four pieces and a crushed tablet.  Increasing the surface area, especially pulverizing the tablet definitely increases the reaction rate (shorter reaction time).

Students graphed reaction times as a function of temperature.  This was a nice straight forward lab and as mentioned before the only thing we didn’t do was the lower concentrations since the reaction times got to long.

 

 

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