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Forensic Science – Bite marks

We had pretty much finished all the ‘interesting’ labs in the ACS Middle School Chemistry curriculum so I dug out a forensic science kit that a friend had purchased for us a year or so ago.  Its one of many kits in the The Mystery of Lyle and Louise, a hands-on forensic science curriculum.  Its made for high school students but the kit I have is for bite impressions, Lyle and Louise Bad Impression Bite Marks Analysis Kit, and the kids just had to measure a few distances to compare bites so it was ok for middle school.  We actually did this in two classes.  During the first class I showed them a slide show I found on the internet about forensic odontology (using teeth/bite marks in forensics) and then everyone made a bite impression in a piece of wax and learned how and where to measure on the bite impressions.

IMG_0107For the second class I read them the story of the mystery of Lyle and Louise which involves a car wreck, a murder scene,  a drug bust and various other bits.  There is a slideshow you can find on the internet premade for this.  I made sure to tell the kids this was a made up story and got the ok from parents before showing the slideshow – all the crime scenes are drawn images so its not graphic or anything.  Each kit you can buy tests different evidence for the same story, so to figure out what happened to the victims you have to do a lot of the kits if not all of them.  The bite mark analysis that we did in class was just to see if one suspect was lying about the bite mark on his arm – did he get it from a guy in the bar or did the victim bite him?  Between classes I took the bite impressions the kids made and separated them into different groups and added the impression that matched the photo evidence, both provided in the kit.  Students had to make measurements from the bite mark on an arm (photo) and then measure the various bite impressions to determine who could have cause the mark on the arm.  There is a spreadsheet you can download to do an analysis of the data – finding the set of measurements that match the photo the best.  I entered the data for each group and it was interesting that two of them had 2 bite impressions that were pretty close to the photo so I told them to look at the photo closely for identifying marks like crooked teeth or missing teeth that would help them make a decision.

IMG_0108This was a pretty interesting lab and I wish the kits weren’t so expensive so we could buy more.  This one classroom kit was $129.  I did see that they now sell a small classroom edition that contains all the experiments for a little over $300 and its good for 6 kids.  So it might work well for a homeschool co-op, everyone pitch in $60 to buy the kit and do the labs together.  When you buy a kit you get access to their online resources.

Overall nice lab kit, just wish the price was lower.

 

 

Honors Chemistry 21 – Acids & Bases

For this lab I basically followed the Modern Chemistry lab: Household Acids & Bases but added a few things.  The lab is in the textbook and can be found in the online resources.  Its a simple enough lab with students testing various household items like dish soap, soda, lemon juice, vinegar, bleach, milk of magnesium, etc. to see if they are acids or bases.  The lab called for us to make a pH indicator out of red cabbage so I did that the night before to save time.  Its very easy to make, you just chop up a red cabbage and place it in a pan full of water.  Bring it to a boil then turn off the heat and let it cool.  Strain it, collecting the lovely purple water which is your pH indicator.  I found this great photo below that shows the color of the indicator for different pH.

red-cabbage-juice
Photo Copyright Fundamental Photographs, NYC, http://www.fphoto.com

I also happen to have a pH meter, litmus paper (red and blue) and regular pH paper, so I had the students test 5 different chemicals with as many methods as they could.  I also asked that they try to get a rainbow of colors with the cabbage indicator like in the photo above.  Here are some of their results.

This lab worked really nicely and the color changes were pretty dramatic.  Bleach turned the purple indicator a dark brown which quickly faded to yellow and eventually went clear (see photo with test tubes).   In most cases the  pH meter reinforced the pH values found with the cabbage indicator and the pH paper (which turns color like the cabbage indicator).  Litmus paper just tells you whether you have an acid or base.

I had the students watch two Crash Course videos before class.

Here’s a good video on sulfuric acid:

We had some extra time at the end of the lab so I demonstrate the power of hydrochloric acid by using it to dissolve aluminum foil, which is the same demo I talked about in yesterday’s post for the intro class.  The photo below shows the foil in muriatic acid (HCl) and the little bubbles of hydrogen gas starting to form.  img_8421

In this video you can see the hydrogen gas escaping and the acid looks like its boiling, but the beaker is very cold to the touch, its just a vigorous chemical reaction producing a lot of gas bubbles.  Near the end of the video you can see that the Al foil disappears completely.

Honors Chemistry 15 – Charles’ Law

Last week we looked at Boyle’s law  – holding a sample of gas at constant temperature while varying the pressure and watching the volume change.  Today we investigated Charles’ Law by keeping the pressure constant and changing the temperature so we could see how the volume would vary.  We used the same 10ml syringes that we used last week but tried to do a better job lubricating the plungers with vegetable oil.  They still seem to get stuck so the students gave them a bit of push/pull/twist to free them and then measured where the plunger came to rest.

img_6574The lab is from the Home Scientist Chemistry kit manual, CK01A, Session VIII-2: Observe the Volume-Temperature Relationship of Gases (Charles’ Law).  To get a range of temperatures we put the syringes and thermometers in my kitchen freezer which got us to -12C,  an ice/water bath, boiling water and cups of water heated in the microwave to get a few points in between.  The students made sure to reset the syringe before each data point and the results of this experiment came out much better than last weeks.  The data analysis was a lot easier in this lab since the only math was converting their measured temperatures in Celsius to Kelvin.   You can see from one set of results below that the data came out very linear, as you increase the temperature of a gas the volume goes up as expected.  Since this was a relatively short lab I talked about percent error a bit before we started and showed them how to put error bars on their data points.  I also had the students graph their data as they went so they could see what temperatures they might want to do to fill in gaps in their graph.  This also allowed them to see when something might have gone wrong (plunger stuck) and they needed to retake a data point.

IMG_6581.jpg

If I only had time for one of these gas law experiments I would definitely recommend this one over the Boyle’s law lab.

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.

img_5664Then 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.

img_5672Next 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.img_5677

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.

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.

img_5524All 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.

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