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Intro Chem 26 – Acid Concentration, Color & pH

IMG_9673This is experiment is from Chapter 6, Lesson 8: pH and Color Change, in the American Chemical Society’s Middleschool Chemistry curriculum.  I almost didn’t do this lab because when I tried it the night before class it didn’t really work that well but it worked great for the kids (I think they were being more careful than I was).  The lab calls for universal indicator so I made some red cabbage indicator (you can find the recipe all over the internet) which is blue-purple around neutral, going to red for acids and green for basic solutions.   Students filled 6 wells in a 24 well plate with the indicator and then made a weak citric acid solution – 5 ml of water with 1 toothpick (used as a scoop of sorts) of citric acid (True Lemon).  They then took a pipette and dropped 1 or 2 drops of the citric acid in well 2, recorded the color and pH.  Then they added another toothpick scoop of citric acid to their solution and so on.   IMG_9654

As you can see in the photo above, the wells of indicator get steadily pinker as they increased the concentration of citric acid, indicating a decreasing pH.  The second well of blue-green is created by doing the same experiment but increasing the concentration of sodium carbonate to make an increasingly basic (higher pH) solution.

This lab didn’t take very long so the kids played some more periodic table battleship.

 

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.

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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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.

 

Intro Chem 22 -Reaction rates

Today’s lab, Clock Reactions,  is actually from the high school curriculum, Modern Chemistry. It starts out talking about time-released medications and how to change the rate of reaction of medicines (their digestion).  So I asked the students, “What could you do to change the speed of a chemical reaction?”  They answered with changing the temperature or the concentration of the chemicals, pH and surface area.  This lab has students drop effervescent antacid tablets into 15ml of water and record the time it takes for the reaction to take place.  Instead of just watching the reaction, students listened to the fizzing sounds it IMG_9127makes (producing gas) and didn’t stop the timers til the fizzing sound stopped.   They did this 1/4, 1/2, 3/4 and 1 whole tablet in cold water and most of them found the reaction took longer than 5 minutes at which point I told them to stop because we were going to run out of time.  They were supposed to repeat the whole experiment for room temperature and hot water as well but we were going to run out of time and tablets if kids did all of them so we just did 1/4 and 1/2 tablet for room temperature and hot water.  As expected the reactions went faster in the hotter water.  Molecules are moving faster and therefore bump into each other more often and are more likely to react.  They also ground 1/4 and 1/2 tablet into powder with a mortar and pestle to see if increased surface area would speed up the reaction and it definitely shortened the reaction time.

IMG_9132This lab was pretty good but asking the students to do 3 temperatures for 4 different tablets sizes was too much.  They should have just done that at one temperature so the only thing they changed was how much tablet went in the water.  Then pick one tablet size, like 1/2 of a tablet, and see how water temperature affected the reaction time.  Finally ground up the same size table and observe its reaction.  Trying to measure all these reactions for 4 different tablet sizes made it overly complicated and made it more difficult to see exactly what was happening.  The other thing I would change is having more jars around to put the centrifuge tubes in.  The tubes have flat bottoms but quite a few got knocked over today and being able to place them in a small mason jar usually keeps that from happening.  The lab also has students do the experiment with 0.1M  HCl but since this was my middle school class, I skipped that part, which from the number of spills we had today…was a good idea.

 

 

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