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September 2016

Intro Chem 03 -Thermal Conductivity

After a two week break, we’re back to class today.  One of the perks of homeschooling is that you can go camping when everyone else goes back to school and have the campground to yourself.DSCF7868.jpg

Today we did the Chapter 2, Lesson 1: Heat, Temperature and Conductivity lab from the American Chemical Society’s Middle School Chemistry.  My grocery store didn’t have styrofoam cups so I bought some insulating cups made from plants (eco friendly – yeah) but they  didn’t do a very good job insulating.  For the experiment we had 4 or 5 metal washers tied together by a string soaking in room temperature water and a separate cup with hot water.  The students recorded the temperature of the water with the washers and the temperature of the hot water.  Then they placed the washers in the cup with the hot water and watched the temperature.  We also had a control cup containing just hot water because if you leave a cup of hot water sitting on the counter, it will cool off all by itself.  The kids correctly predicted that the washers should bring down the temperature of the hot water.  The problem is that the control went down by the same amount.  So we decided to double up on cups for the second experiment to increase the insulation value and we put  the lids on the cup.

The second experiment is just the reverse of the first one.  This time the washers were left in very hot water and then placed in room temperature.  The water’s temperature went up briefly before it started to cool.   I expected the results to be bit more dramatic then they were.  I think using ice water and very hot water might work better.

Before we did the experiment I held a saucepan and metal spoon in my hand and asked the students what would happen if I left the spoon in the pan while cooking.  They all shouted that it would get hot.  I then held up a wooden spoon and asked the same thing.  They all instinctly knew that it wouldn’t get as hot as the spoon.  So I talked about how heat is conducted differently by different materials and metals tend to be good conductors of electricity and heat.

The ACS curriculum actually has some links to some nice little videos showing the temperature of molecules and how they transfer energy to each other.

http://www.middleschoolchemistry.com/multimedia/chapter2/lesson1#heating_washers

 

 

 

 

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Honors Chemistry 03 – Chromatography

So today we learned from our mistakes.  We did the Chromatography lab (Session I-2) from the Home Scientist chemistry kit.  This lab involved doing two separate chromatography labs, the first one involved dabbing permanent markers (Sharpies) on img_4392chromatography paper and then placing the paper strip in a tube with a little bit of isopropyl alcohol in the bottom. As the alcohol moves up the paper it takes the ink with it but if the ink is made of different types of dyes they may separate as seen in this photo where the green and blue dyes separated.  This lab was pretty straight forward and most of the kids had done this before.  The only problem was not putting the marker dot far enough up on the paper and it ended up under the alcohol line and just mixes with the alcohol, or if your tube got knocked over and you end up with ink going all over.

The second part of this lab was a bit more complicated and we weren’t careful enough with our chemicals.  For this lab we used hot water for the solvent and instead of ink you use Copper (II) Sulfate, Lead (II) acetate, Iron (II) sulfate and Iron (III) chloride.  Once again if you didn’t put the chemicals far enough up on the paper img_4399they ended up under the water line and the experiment doesn’t work.  These chemicals are pretty much invisible on the paper so you don’t know how far the chemical has moved up the paper until you ‘visualize’ them by putting another chemical on the paper that reacts img_4403
with them and turns them brown, blue or yellow.  We had trouble with mixing up pipettes and contaminating samples and using the wrong chemicals to ‘visualize’ the chromatography strips.  Here’s a strip (on left) with the Copper sulfate and Lead acetate dropped on the strip before being dipped in  water,  and after  (photo on right) the separation and adding the Potassium iodide to make the colors (brown and yellow) appear.   You can see that the Copper (II) sulfate moves much further up the paper than the Lead (II) acetate and therefore has a higher retardation factor (Rf = distance sample travels/distance solvent travels).  We didn’t have too many problems with the Copper sulfate and Lead acetate but the strips with the Iron (II) sulfate and Iron (III) chloride had many problems.  IMG_4396.jpgThe first time through we hadn’t read the lab carefully enough and wiped both Fe (II) and Fe(III) sides of the strip with Potassium ferricyanide,  but we were only supposed to do that for Fe(II). We were supposed to use sodium ferrocyanide for the Fe(III) side of the strip.  Unfortunately we must have contaminated the bottles of chemicals because it never worked again after the first time. So the very first try with the Fe(II) was the only one that turned blue.  The photo below is the one where we used the Potassium ferricyanide on both sides, so it worked on the Fe(II) and gave a nice blue steak.  img_4400We did use each Q-tip once but we made the mistake of dipping them in the bottle instead of using a pipette to drip the chemicals on the Q-tip so I think we contaminated the ferricynaide chemicals.  I’m not a chemist, so I’m learning with the kids as we go.  But we did figure out what we did wrong and hopefully won’t make the same mistake again

For class this week I had the kids read either Chapter 3 in Modern Chemistry or Chapters 3 & 4 in Ian Guch’s Chemistry: the Awesomest Science and watch the Crash Course Chemistry videos #3 and #37.

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