Intro Chem 10 – Chemical Reactions

We haven’t been doing much actual chemistry in class yet but today was Halloween so I decided to do a bunch of chemical reaction demonstrations and then have the kids make glow in the dark slime… complete with eye balls.

I found an interactive notebook lesson that we did at the beginning of class.  The lesson is Signs of Chemical Change from Chemistry : Compounds, Bonding & RXNs by Stephanie Elkowitz and I bought it on teacherspayteachers.com.  It has different test tubes that you cut out and each one has something like, odor, light, bubbles… things that can indicate a chemical reaction has taken place.  They cut them out and make a pocket in their notebook to hold them. While they were cutting and putting it together I started talking about the different types of chemical reactions that can occur – basically a simpler version of the talk I gave for the high school class.

Then we did some chemistry.  We started with burning some magnesium ribbon, which is a synthesis reaction – magnesium plus oxygen produces magnesium oxides.  After watching the demonstration the students went back to their notebooks and described what they saw, including the clues that a chemical reaction had taken place, in this case a very bright light was produced and there was a color change.

The second reaction I showed them was the copper wire that we had put in silver nitrate last week during the high school class.  The copper wire was completely covered in silver and many students guessed that it was a fish or a leaf inside the tube.  I explained that it was a single displacement reaction, the copper displaces the silver in the silver nitrate solution and you end up with bits of silver forming on the copper wire.  Then we dripped silver nitrate solution into salt water and watched the precipitate, silver chloride form and sink to the bottom.  This reaction is a double displacement with the silver and sodium atoms switching places to form silver chloride (solid) and sodium nitrate in solution.

Next we made elephant toothpaste – the instructions I followed can be found here on Science Bob’s website.  Steve Spangler also has videos and instructions on his website. I used about 15 ml of hydrogen peroxide (40 Volume bought at Sally Beauty Supplies – its a higher concentration of hydrogen peroxide than what you would buy in grocery store), a couple of squirts of dawn dish detergent, and dripped some food coloring down the side of the cylinder.  Then put a tablespoon of yeast in warm water, stir a bit and pour into cylinder.  If your ‘toothpaste’ is too runny try putting less water in with the yeast.  This is an example of decomposition reaction because the hydrogen peroxide is breaking down into water and oxygen – the yeast acts as a catalyst – helping the reaction along.

Lastly, we did the black snake demonstration.

For this experiment I followed the instructions of the Crazy Russian Hacker.

Since today was Halloween I let the kids make glow in the dark slime for their own chemical reaction.  The instructions are on the American Chemical Society’s website.  I added some eyeballs that I found at the local halloween store.

No class next week, but we’l be back in two weeks with the kids presentations on the elements.

Honors Chemistry 10 -Types of Reactions

Today’s lab was a lot of fun, it was basically an ooohhh, aaahhh day.  The lab, Six Types of Reactions, is from Ian Guch’s 24 Lessons that Rocked the World.  We couldn’t do all six because some took me out of  my comfort zone and I don’t have a fume hood in my kitchen.  But Ian did recommend some other chemical reactions that we did instead and we watched some videos on youtube for the ones we didn’t do ourselves.

But before we started the labs I went over writing a lab report and asked the older students  (juniors and seniors) to choose one of the labs we’d already done and try their hand at writing up a report for next week.  I gave them this link to how to do a write up and an example lab report from Liberty High School.  The procedure made me cringe a bit since every sentence begins with ‘The’, but I thought it was about right for a high school lab report.   Purdue actually has an awesome website, including videos, on writing up lab reports but its way more than they need at this point.

For this lab, I set up 5 different experiments.  The first one was a synthesis reaction where the students grabbed a SMALL piece (3 cm) of magnesium ribbon with test tube tongs and held it over a butane burner.  The magnesium burns incredibly bright as it reacts with oxygen to form magnesium oxide, a fine white powder.

The second setup involved placing a small chunk of copper sulfate hydrate (dark blue) in a crucible and heating it up to drive out the water – this is an example of a decomposition reaction.

Before heating

After heating

The third reaction was done as a demonstration because I only one piece of copper and very little silver nitrate.  I made a 0.1 M solution of silver nitrate in a small centrifuge tube and place a piece of copper wire into the tube.  This is an example of a single replacement reaction, the copper switches place with the silver and you end up with silver precipitate (solid) and the copper becomes copper nitrate (in solution).  As you can see in the photo the copper wire grew silver fuzz!  You can see a little bit of the copper wire sticking out of the solution.

We also did a double replacement reaction with the silver nitrate solution.  For this one the students used a disposable pipette to drop the silver nitrate (0.1 M) into salt water (1M).  The silver and sodium switch places forming silver chloride (solid) and sodium nitrate which remains in solution.  The silver chloride forms a white precipitate immediately and slowly falls to the bottom of the beaker.

The fifth experiment was an acid-base reaction.  Students used a disposable pipette to place 2 drops of sodium hydroxide (0.1 M NaOH) into a watch glass, then one drop of indicator which turned the NaOH bright pink.  Then they dropped hydrochloric acid (0.1 M HCl) into the watch glass and the solution turns back to clear.

We didn’t do a combustion lab because two of the students had already demonstrated that reaction during the first lab back in September.

We also tried a decomposition lab from the home scientist CK01A Instruction Manual but we were not successful.  This was one of the easiest labs, place baking soda in a beaker, place on hot plate to drive out the water.  Water drops were supposed to form on the lip of the beaker but we never got any.  We were also supposed to test for carbon dioxide inside the beaker but all those failed too.  I’m not sure what went wrong, perhaps our hot plate wasn’t getting hot enough? Though I kind of doubt that since it felt like it was heating the whole room.  But I did show the students how the cobalt chloride test paper turned pink when it touched water and would turn back to blue when it dried out.

Tyler Dewitt has a great video (as always) on major reaction types.

Here are some videos we watched in class on some reactions we did and some I wouldn’t do, like exploding hydrogen balloons.

This class was a lot of fun and I think I’l do some of these same reactions as demonstrations for the middle school students next week.

 

Intro Chem 09 -Periodic Table Part II

I went back to the American Chemical Society’s (ACS) Middleschool Chemistry curriculum and found this great activity for the periodic table that makes the students really look at the periodic table and understand what information the atomic number and atomic mass gives them.  This is from Chapter 4, lesson 2: The Periodic Table.  First I had them do a simple handout from Atomic Structure for Interactive Notebooks, where they label the atomic number, atomic mass, element name and symbol for one element.  Then we filled out a partial periodic table putting in the number of protons, neutrons and electrons for the first 20 elements.  This partial periodic table is provided in the ACS lesson.    Since the proton number is equal to the atomic number I had them fill all of those in first and then since the atoms are neutral the number of electrons must be the same as the number of protons.  Now that I’ve done the lesson, I think I should have done neutrons 2nd and left the electrons for last because the kids got confused and kept trying to add the number of protons and electrons to get the number of neutrons.  If we had done the neutrons before the electrons, those numbers wouldn’t have been there to confuse them.  To find the number of neutrons they had to look at the atomic mass, round it the nearest whole number and figure out how many neutrons they had to add to the protons to get the mass number.  Since they had to do this 20 times, I think it was pretty well drilled into them by the time they finished.

All this was just setting them up for the activity, where each pair of students were given 20 cards with clues on them, like ‘this atom has 15 protons’, and then find the element that the card goes with.  This caused a bit of chaos in the room as 10 kids ran around my kitchen trying to find elements but I think they learned quite a bit and had some fun doing it.  My 16 year old son and I went through and found cards in the wrong place and kept handing them back to students who had finished with their cards.  A couple of the students who really had this process down were given cards that discussed the electron shells and had more complicated clues.  I think this would have worked a bit better if I had put color dots on the cards so I knew which teams had which cards. Then I could have given out a prize, or at least recognition for the team who got the most right – a little incentive for being more careful in their card placement.   Another thing that would have decreased the chaos is have 2 teams at a time putting their cards up instead of everyone at once.

Honors Chemistry 09 – Percent Composition

Modern Chemistry Chapter 7, Chemical Formulas and Chemical Compounds was fairly boring, the first half of the chapter was all about chemical names which really put me to sleep. I’m not about to memorize that so I’m not asking my students to either.  The last part of the chapter was about molar mass and percent composition, some of which we’d already covered earlier this semester.  I did give the students a worksheet about naming covalent compounds that I got from Covalent Bonding Interactive Graphic Organizers for the Chemistry Notebook or Lapbook by Bond with James (teacherspayteachers.com). The worksheet had half a page explaining naming rules and then half a page where the students had to name the compound or write out the formula.  One of the students did find one typo on that page, the answer key had a different compound than the question sheet.

The lab for this class, Chapter 7 Percent Composition Lab,  was taken from Ian Guch’s 24 Lessons that Rocked the World.  I really liked this lab, it was fairly straight forward, measure the mass of your container, the mass of container + epson salts, heat epson salts then find mass of what’s left.   Heating the epson salts drives out the water and the change in mass is very significant, so its the not typical small change that you might miss if you’re not careful.  The visible change is also very big and got lots of suprised ‘Wow!’s from the students.  I hadn’t done this lab before so I hadn’t known what to expect either.  One of the students wondered out loud what it would like under the microscope, so I pulled it out and we took some pictures. The photo on the left with the large crystals is hydrated magnesium sulfate (epsom salts before heating), and the photo on the right is anhydrous magnesium sulfate (epsom salts after heating).  The microscope was on the same magnification for both images so you can see the change was pretty drastic.

epson salts before heating

epson salts after heating

The lab handout steps the students through the process of calculating the percent composition of water for the epsom salts and then finding the chemical formula.  The last page of the lab includes a worksheet with additional practice in calculating percent composition which I assigned as homework.

This is a great lab for homeschoolers since all you need is epson salts, which you can buy at a grocery store, a scale (and a kitchen scale would probably work since the mass change is so large) and a heat source.  We didn’t get exactly the right numerical answer for the lab, our numbers were all a little low but the students quickly realized that meant they probably didn’t heat the salts long enough so there was still some water left in the cruicible.  We left the lids on the cruicibles while heating, so we didn’t watch the reaction and just heated the 10 minutes stated in the lab handout.  I would like to try this again with the lids off so we could tell when the reaction is done and see if we get better numbers.  The only safety concern with this lab is the heat source.

Tyler DeWitt has a nice set of videos on how to calculate percent composition.

Intro Chem 08 – Periodic Table

This class was a slightly simpler version of the high school class.  We started out watching Crash Course Chemistry on the Periodic Table. I stopped it  a few times and we discussed the different groups and I drew electrons in the different shells for some of the groups.

Then we did a quick run through of the Coloring the Periodic Table Families slideshow that can be found on middleschoolscience.com.  And it looks like she already updated that slideshow, I really need to go check her website before class to get the latest stuff!  I did not have the kids color as we went through the slideshow.  When we were done with the slideshow I taped a copy of a periodic table to my whiteboard and we all colored in the different families together and made a legend.  

I also gave out this really cool periodic table with pictures for each element showing what the element is used for, and had them tape that in the back of their book for easy reference. The website, elements.wlonk.com, where I found this has quite a few nice printables, including element cards.

The last thing we did was a worksheet called Periodic Table Notes: Determining # of shells and valence electrons from middleschoolscience.com (again the link goes to an updated version of the file I used).  Just like the high school class this made the students take a close look at the periodic table, looking up elements and finding their period, # of shells, their group number and # of valence electrons.

Great apps for playing around with atoms and elements include the NOVA Elements app where you can add the correct number of protons and electrons to make a particular element and of course the Elements app by TouchPress is beautiful.