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Secular Science Resources for Homeschoolers

Honors Chemistry 06 – Flame test

The flame test lab, where you place different chemicals in a flame and produce different colored flames is always a fun lab and one I’ve done many times before.  But this time I used another lab, Chapter 4- the Flame Test Lab, from Ian Guch’s 24 Lessons that Rocked the World.  op-kit01The kit I had purchased years ago from the Home Science tools website comes with the chemicals and a simple spectroscope that will let you estimate the wavelength of the light.  This kit only has you soak the sticks and then stick them in the chemicals so that a bit of it ends up on the stick, which you then put in the flame.  Ian Guch’s lab has the teacher make up 0.5 Molar solutions of each salt with distilled water.  Then the sticks were soaking in the solutions and the flames were much better than we had achieved in previous flame tests.  I also added some cupric chloride, as a 6th chemical, that I bought separately because it produces a beautiful green flame.img_4767  The little butane burners worked really nicely for this lab since they don’t produce much of a flame.

I used 50 ml centrifuge tubes to mix the chemicals in and we used wooden skewers (cut in half) instead of toothpicks.  I mainly used the wooden skewers because the centrifuge tubes were tall and I wanted the students to be able to pull out the skewers with tongs easily.  It also kept them from having to get too close to the flame.  A couple of the chemicals we used are hazardous so the students used tongs to grab the skewers.  You do NOT use gloves because the gloves could melt on to your hand if you got too close to the flame.  We did make sure long hair was tied back and aprons and goggles were worn.

img_4738The lab entailed looking at 6 known, labeled chemicals and determining the color of the flame.  Some of the students used the spectroscope to also record the wavelength of light since some of the colors were pretty close.  Then they had to identify 6 unknown chemicals by looking at their flame test results.  Some of them like the cupric chloride were easy to identify (the solution itself is blue) but there were a couple of chemicals that gave orange flames and two that gave red flames.

IMG_4783.jpgYou can see in the photo above that I had the centrifuge tubes in glass beakers or jars to keep them from falling over.  The beakers were themselves contained in a plastic container.  The tubes had to  be open at the same time so the skewers could be soaking in the chemicals and I was afraid they would fall over and that would be in the end of the lab.  This set up worked really well and we had no spills.  I had two skewers in each tube and since only one person was doing a flame test at a time, it was relatively easy to make sure they put the skewer back in the right tube.

At the end of the class the groups which correctly identified all 6 chemicals were the same groups that used the spectroscope to estimate the wavelength, so if you have a spectroscope available, its worth doing.  You can make your own spectroscope, there are a lot of DIY instructions available on the internet.  We used this one a year or two ago, papercraft spectrometry starter kit, but I never had much luck with the computer part of it. It just seemed to take forever to upload the files.

Before we started the lab we discussed why the chemicals give off light (excited electrons dropping down to the ground state) and why different elements give off different colors (elements have different numbers of electrons in different levels so the energy/color given off is different).  We also talked about why this is useful, identifying unknown chemicals/impurities in water or learning about the elements in stars.

I suggested students watch these videos before class:

Crash Course Chemistry #5, the Electron

Wave-Particle Duality and the Photoelectric Effect by Professor Dave Explains

Quantum Numbers, Atomic Orbitals, and Electron Configurations by Professor dave Explains.

 

 

Intro Chem 05 -Water & Ice

We started class by watching a couple of videos about water and phases of matter:

What Is An Ice Bomb? (Mr. Wizard)

States of Matter by Veritasium

Why does ice float in water? – George Zaidan and Charles Morton

I’m always a bit annoyed when science curriculum say there are only 3 phases of matter, gas, liquid and solid, so I showed this video on plasma and I told the students about liquid crystals which share characteristics of both solids and liquids.

Plasma, The Most Common Phase of Matter in the Universe – SciShow

For this class we used the lab, Chapter 2, Lesson 4: Changing State – Freezing  from the ACS Middleschool Chemistry curriculum. Students put rock salt and ice layers in an metal soup can.  The salt lowers the freezing point of water so the temperature of the salt/ice img_4709mixture will drop below zero degrees Celsius. Once the students observed ice forming on the outside of the can they measured the temperature of the ice/salt mixture.  While waiting for ice to form on the cans the students made water molecules out of stryofoam balls and toothpicks.  They also cut and pasted the lab sheets into their notebooks and filled out a table on the properties of water molecules in their liquid vs solid form.

Honors Chemistry 05 – Conservation of Mass

img_4618This lab is from Ian Guch’s 24 Lessons that Rocked the World and as you can see from the photo on the left the students had quite a bit of fun with this lab.   The purpose of the lab is to demonstrate the Law of Conservation of Mass, which states that the sum of the masses of the reactants will equal the mass of the products of a chemical reaction.  Unfortunately this can be difficult to demonstrate since its hard to capture gases created in a chemical reaction and we frequently lose some material in transfering chemicals from container to container, etc.  But we can try our best and see how close we can get.

For this lab we needed 2M concentration of acetic acid, which I made before class.  The lab called for sodium carbonate, not sodium bicarbonate so we had to bake the baking soda in the oven at 200F for 45 min which drives out carbon dioxide and water.  Students measurd  13 g of the sodium carbonate and placed it in the finge of a glove using a funnel.  The finger was then tied shut with rubber bands to keep the sodium carbonate contained.  The 2M of acetic acid was poured into a beaker (250ml) and the the glove was fitted over the beaker and secured with rubber bands. img_4602 The entire apparatus was then weighed on the scale so we would have the mass of the reactants before the reaction.  Then the rubber bands were removed from the glove and the sodium carbonate was dumped into the acetic acid.  Much fizzing and bubbling occurs as the glove fills with carbon dioxide.  The first group had a lot of gas escape from their glove and the liquid fizzed up so much it overflowed the beaker and escaped from the glove.  The second group had similar results but the third and fourth group having seen the leakage used bigger beakers and managed to contain their liquid.  Another thing we did after watching the first group’s reaction is weigh EVERYTHING, including the aluminum pan so if liquid did escape the beaker it would still be contained in the pan and the mass would not be lost.  The fourth group had their glove come off so they lost quite a bit of gas.  I would recommend using a larger beaker, 500ml and a larger latex glove and make sure you secure it with a couple of rubber bands.  The third group who had no visible leakage from the system lost only 3 grams of mass which is pretty dang good. You can watch their experiment in the video below.

The other groups lost about 6 grams.  Trying to prove conservation of mass in the lab is fairly difficult since no matter how many rubber bands we put on the glove we probably lose some gas thru the glove and the gas is buoyant so its not exactly putting its full mass on the scale.  But this lab was very exciting and the students enjoyed seeing the glove inflate and I have to say I’m pretty impressed with the strength of the latex gloves.

Here’s a nice Ted-Ed talk on the law of conservation of mass:

Intro Chem 04 – Combustion

OK, so I have to admit the ACS Middleschool science curriculum is really starting to bore me. The labs we were to do this week basically involved watching wet paper towels dry (evaporation)…. um, no thanks.  So we watched candles burn instead.  I did talk about evaporation and condensation (something that doesn’t happen in dry California that much) but we left it at that.

RTEmagicC_CondensingCandle-candle.png.png
NakedScientist.com

The lab we did do comes from Middleschoolscience.com and is called the Candle Observation Lab and she has a link on there to the NakedScientist lab called Getting Water from a Candle.  The NakedScientist website has an audio recording about the experiment that you can listen to as well as a short clip of placing a glass over a candle.

This lab mainly consisted of writing down observations, first before the candle was lit (describe the wax, the wick, does it smell? Color? Texture?  Used or unused? and drawing the candle.  Then I lit the candles and they observed them over 10 minutes, again making a drawing and describing the flame, melting wax etc.  After putting a glass beaker over the candles they once again described what they saw and made a drawing… img_4593or a series of drawings.  The students weren’t sure if the beakers would actually extinguish the flames since they didn’t form a perfect seal with the plates but the flames indeed got smaller and went out pretty quickly as smoke filled the beaker and water vapor condensed on the glass.rtemagicc_condensingcandle-extinguished-png

The students knew the fire needed oxygen but they thought that the oxygen was the fuel, so I explained how as the wax melts it gets sucked up into the wick and becomes the fuel for the fire, which is why the amount of wax left in your candle decreases til there is nothing left if you leave it burning long enough.

I provided a handout for their notebooks with the images from the NakedScientist like the one on the left showing the chemicals being used up and produced by the fire.

We also used a page from an interactive notebook bundle I got from TeachersPayTeachers.  Combustion is from the Chemistry Interactive Notebook by Stephanie Elkowitz. Its a nice simple flap where the students put the necessary ingredients for combustion on the left and the products on the right.This really helped since it has Oxygen and Fuel on the left, which most students thought was the same thing, but when I asked what is used as fuel for a campfire they knew it was the wood. Under the flap we listed some different fuels and the fact that combustion is an exothermic reactions (gives off heat/energy).

We had 30 minutes left so we did an activity on physical changes versus chemical changes.img_4595

Each pair of students were given a set of cards and asked to separate them into two piles, the cards that demonstrated a physcial change (like boiling water – its still water, its just in a different physical form) and the cards that showed a chemical change (like baking a cake).  Once they had the cards sorted correctly, which took a few trys, they wrote down the answers on a form for their books.  Some of the students decided to paste the cards into their books which was a great idea. I got this activity from Stephanie Elkowitz’s Chemistry Interactive Notebooks as well.

We showed a few videos in class, 2 having to do with how Astronauts can make water in space (or on Mars, like Mark Watney in the Martian…. I love that book!)

And this video on how to make water with combustion.

And lastly, I asked the students why is the candle flame that particular shape? And what would it look like on the space station?

 

 

 

Honors Chemistry 04- How many molecules?

This lab came from Ian Guch’s 24 Lessons That Rocked the World, Chapter 6 – Moles, Molecules, and Grams Lab. Before class I prepared film canisters with 5 grams of salt, sugar, water, gypsum sand and isopropyl alcohol.  img_4531The students had to determine how many moles and molecules of each substance were in the each container.  We used  a digital kitchen scale and a triple beam balance (pictured above) to measure the mass of each sample which was poured onto a watchglass.  The kitchen scale is not terribly percise, only measuring to the nearest gram, but this lab was more about how to do the calculations then making precise measurements.   They then had to find the molar mass, which involved looking up the atomic mass of each atom in the chemical formula for each sample and adding them up.  Dividing the 5 grams (or whatever the mass was that they measured)  by the molar mass told them how many moles they had, and then all that’s left is to multiply by Avogadro’s number (6.022×1023) which is the number of molescules in one mole of anything, to get the number of molecules. This lab mimicked the homework they had for chapter 3 from Modern Chemistry, but put a real substance in front of them.  The older kids, mostly  juniors, had no problem with this lab but as I suspected, the younger students weren’t sure how to do the calculations, specifically how to enter avogadro’s number into their calculator so this was a good activity to do in class.

This activity showed that 5 grams of water has a lot more molecules in it then 5 grams of sugar since each sugar molecule (model on left) has a larger mass, it therefore takes fewer of the, then say water molecules,  to get to 5 grams.  Students also learned how to use their calculators.

d-glucose-chain-3d-balls
sugar molecule (wikipedia)
ball_and_stick_water_molecule
water molecule (middleschoolchemistry.com)

 

 

 

 

 

There is a great video by Tyler Dewitt explaining how to do these calculations.

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