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March 2017

Honors Chemistry 28 – Redox Reactions

So I had a terrible time with this chapter (Chapter 19: Oxidation-Reduction Reactions in Modern Chemistry) and spent a lot of time on youtube trying to get a grip on this stuff.  I realized part of my problem was that I didn’t understand the oxidation states well enough so I backed up a bit and these videos by Khan Academy helped me the most.

Tyler DeWitt has a pretty good video as well:

Most of the labs for this subject involve watching iron wool rust over several days (lab X-2: Observe the electrochemical Oxidation of Iron)… not exactly conducive to a two hour class.  So I had my son set up one of them yesterday so the students could just observe the results in class today and then we did lab IV-1: Observe Oxidation States of Manganese, from the home scientist’s chemistry kit manual, CK01A. The first lab was just observing a bit of iron wool in 6 different test tubes with various combinations of water, salt and oxygen available to the wool.IMG_9511

The second lab involved looking at different oxidation states of manganese by putting some in 4 different wells of a reaction plate along with some other chemicals.  This was a nice short lab (only 4 wells!) and you get some significant color changes (see photo below) and even a precipitate in one.IMG_9515IMG_9522

Besides these two labs I also happened to have a chemiluminescence kit which contains luminol solution and hyrdogen peroxide.  Luminol emits light when its oxidized.  I poured approximately 20 ml of luminol into a small beaker and then used a dropper to squirt hydrogen peroxide (Salon Care 40 volume clear developer, 40% hydrogen peroxide, not the weaker stuff that came with the kit) into the beaker – this is done in a very dark room – and the solution glows a very nice blue for a minute.  It probably would have been brighter if my solutions hadn’t been so old. I got this kit a year or two ago and the box says it has a shelf life of a year.
I also spent about 20 minutes lecturing on oxidation states and going over examples from the textbook on how to figure out oxidation states and whether or not a reaction was a redox reaction or not.

 

Intro Chem 25 – Identifying unknowns & Elements 4D

IMG_4495I had two activities planned today so half the kids played with the app Elements 4D while half did the lab from the American Chemical Society’s curriculum.  The Elements 4D app apparently has been around for awhile but I just heard of it last week on a facebook page for science teachers.  Its FREE and its awesome!  You print out 6 different blocks, each block has 6 different elements on it, cut them out and fold them to make blocks – I used tape instead of glue.  After you download the app you use the device’s camera to look at one of the blocks, the app will recognize it and then ‘animate’ the block, showing what the element looks like even as you pick up the block and move it around.  The developer, DAQRI calls it augmented reality and its very cool.  Even better, they have FREE lesson plans you can download and when you put two different elements that react in front of the camera it will tell you the compound it can form.  When you push the blocks together so that they touch, they ‘react’ and the pictures change to show the compound.  You can see in the photo below zinc chloride looks like a powder.IMG_9500

I had the students fill out a table with random elements of their chosing.  They pick a block, put it in front of the camera and record the name of the element, its group number (column of periodic table), its color and state of matter (liquid, gas or solid) at room temperature.  Then they tried to find combinations that would react and had to record element names and group numbers for both.  A couple of the kids had ‘Aha!’ moments when they saw that elements from group 1 (Na, K, Li) all reacted with Cl from group 17 because group 1 elements have an extra electron they would like to get rid of while group 17 ‘wants’ an extra electron to fill their outer most shell.  I may actually have my high school class do this activity as well tomorrow.

The lab students did was Chapter 6, lesson 6: Using Chemical Change to Identify an Unknown from the ACS curriculum.  Students are to react 4 different powders with 4 different liquids and record the results – bubbles, color changes, etc.  The lab says to do it on a piece of wax paper or laminate a grid but I used 24 well reaction plates since I had them.  I already had a template I could print out for the kids but went ahead and labeled the columns and rows for them.well plate unknown

Students put one powder in the well plate at a time, so they put roughly 1/4 spatula of baking soda in the first column, wells A1, B1, C1 and D1.  Then they took a pipette and dropped 5 drops of water in A1, got a different pipette and put 5 drops of vinegar  in B1, and so on with the iodine solution (100 ml of water with a few drops of iodine) and the pH indicator. I did not have any universal indicator but had some bromothymol blue which goes from yellow (acid) to blue (base) which worked fine.  After recording their observations on the chart they filled in the next column with the next powder and tested it with the different liquids.IMG_9489

When they had tested all four powders they were given an unknown powder and tested it the same way and were able to determine what it was by comparing to their previous results.

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These two activities worked well together since neither took up a whole class period and it kept the kitchen counter, I mean lab table, from getting too crowded.

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

 

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