Chemical Proportions and Electrolysis

In preparing for Middle School Chemistry with our co-op our family we are going through Matter and Energy: Principles of Matter and Thermodynamics . This volume has two chapters about chemical reactions and the periodic table so it makes a good transition.

The first chapter is about the Law of Conservation of Matter, and while we just read the chapter I've been inspired by something I found here.  I modified it for homeschoolers, taking out much of the school jargon and requirements, and posted it here.  I hope to try it and blog about it soon.

Meanwhile, the second chapter is "How the Elements Combine."  Proust first figured out that chemicals combine by mass in definite proportions.  Dalton realized that some chemicals combine in several but definite proportions, a fact that fit in well with his proposition of matter being made up of atoms.  Next Gay-Lussac showed that gases combined in the same proportions by volume, leading to his law stating that equal volumes of gases have equal numbers of atoms (Avogadro figured out how many.)

This was all well and good, but I was not sure how much they got from this chapter.  I did not have the materials the book listed to carry out electrolysis.  I did an Internet search and found that some people used pencils with both ends sharpened, making holders from Styrofoam trays or cardboard, all powered with a 9V battery.  (See here and here.)  I wanted to capture the gas as was done in the book so we could test them, so this is what I did:

I filled a measuring cup with water and added a teaspoon of salt.  I attached a piece of aluminum foil to one end of two wires with alligator clips. I filled the test tubes with water and placed them over the foil pieces, using the top of the test tube rack to hold them upright.  Finally I connected the other end of the wires to each terminal of a 9V battery.  As you can see at the top of the test tubes gas began to collect.

My boys knew water was H2O, and that meant 2 molecules of hydrogen and one of oxygen.  I explained that electrolysis was "splitting" water with electricity.  I posed the question, "How do you know which gas is collecting in which tube?"  We went through the chapter again.  Proust and Dalton both worked with mass while our experiment was based on volume.  We discussed more about Gay-Lussac's law and asked how definite proportions relate to the creation of water with H and O.  The wheels started turning and they then knew for certain that the tube with more gas had to be the hydrogen.

I do suggest a lantern battery for this, though, because the 9V ran out when only a fourth of the hydrogen tube was filled.  But I am actually a bit glad.  I pulled it out of the water, let the water fall into the measuring cup, lit a match and put it into the mouth of the tube.  The loud whistle and pop was impressive enough to prove that indeed it was hydrogen.

Charles, Boyle, Divers, and Balloons

If you scuba dive, you know these gentlemen; even paramedics are taught their laws when learning about diving-related emergencies.

They are introduced in chapter 3 of Liquids and Gases: Principles of Fluid Mechanics.  Solids and liquids, in general, are non-compressible; gases, however, are and that changes pressure and density.  Robert Boyle invented the air pump, something with which any child that plays with a ball or rides a bike is familiar.  His law states that the volume of a gas is inversely proportional to its volume, if held at a constant temperature.

Taking what we learned from Archimedes, Pascal, and Boyle, we created something named after Rene Descartes--a Cartesian Diver. The book shows the same principle using an eye dropper, but this example in Gizmos and Gadgets is much more fun, if it is a bit more work.











Supplies
1 small foil container
1 bendable straw
1 small paperclip
A small amount of modeling clay
Scizzors
2L bottle with a cap filled with water

I used a small foil container to cut out my 3 inch "diver." Next I cut off the bendable portion of the straw, leaving about an inch on either side.

I used the paperclip to attach the straw to the diver by first clipping one side of the straw and then clipping that onto the diver.  I then gave the diver some clay boots to weigh it down a little but not have it sink altogether.  You can see in the picture that when I put it into the water it bobbed at the top; I just pushed it in a little and put the cap on.

Archimedes taught us that objects float by displacing the fluid they are in, so that the object is less dense than the fluid.  Pascal taught us that water exerts pressure in all directions and is basically non-compressible. Boyle taught us that gases are compressed, and that compressing them increase the pressure and the density.  Our diver has a straw tank of air and is surrounded by water.  What happens when you squeeze the bottle?



The chapter wraps up discussing the effect of temperature on gases. Jacques-Alexandre-Cesar Charles, while ballooning, noticed that hot air expands, but the law named after him was first stated by two other great scientists, John Dalton and Joseph-Louis Gay-Lussac. Charles law states that for a constant volume of gas, the pressure of the gas is directly proportional to the temperature. While I did this with the group, I also did it awhile back with my boys and the videos came out better:







ExploreLearning has  two Gizmos to reinforce these concepts: Temperature and Particle Motion and Boyle's Law and Charles' Law

Pascal and Liquid Pressure

Chapter 2 of Liquids and Gasses has lots of fun water experiments.  Because the weather was not conducive to being in it, we used the bathtub.  We punched holes in a milk jug and watched the water shoot out father from the bottom hole than the top hole.  We also poked a hole in the bottom of one cup and the side of another to demonstrate that pressure is in all directions.  I thought this would be rather simplistic, but I underestimated boys' fascination with water.

The rest of the chapter we discussed.  The illustrations in the text are great, but I wanted to find or rig a container similar to what is pictured in the book with the connected water columns and the piston.  They got a basic understanding of the concept but I extended it to remind them that what they gain in strength they have to make up in distance, just like other simple machines.  A simulation or demonstration would have gone a long way here.

They really liked the tie in to hydraulics, amazed that this simple concept is used to create the brakes of a car.

They so enjoyed fluid mechanics that the following week one of the boys brought in a hydraulics kit that they spent the class exploring.  Something about boys and water...

Density and Archimedes Principle

Eureka!  The Archimedes Principle is about density and buoyancy, but this is one section of the book where the demonstrations did not look promising.  Based on the illustrations, it looked like the water would flow over the top and just run down the sides of the glass rather than collecting in the pie plate.  Maybe if I used a cup with a rim wider than the base it would work.

I thought about getting a set of density blocks for a demonstration but in the end I decided to use computer simulations instead. Both ExploreLearning and Adaptive Curriculum have several great simulations covering density and buoyancy.  PhET has one for buoyancy and another for density that are free, as is the Floating Lab.

You could also read Archimedes and the Door of Science by Jeanne Bendick along with the first chapter of this book.  The details of what happened when Archimedes figured out the principle named after him are in it as well as Fleisher's book.

Angular Momentum with Zomes

The final section of Objects in Motion is about angular momentum.  We read this section and discussed how points farther from the center move faster than those closer.  We also had a spinning chair in the room that they made use of to show how they spin faster with their limbs closer to their bodies.

There's a lot you can do with spinners to supplement this section.  We used Zomes to build spinners, seeing who could build the one that spun the longest.

Next, Liquids and Gases...

Conservation of Momentum

Objects in Motion, Chapter 5 part 1, Conservation of Momentum.

I turned to a favorite book of mine, Gizmos and Gadgets, and found a bunch of activities relating to this chapter. Simple things, like giving them three coins--two pennies and a nickle--and challenging them move one penny using the other penny without them touching each other. They tried all kinds of things before finally figuring out how to use then conservation of momentum to do it.


And more complex things, like creating Newton's Cradle using marbles and an egg carton ramp. There's just something fascinating about watching spheres collide!

>

We finished up building a simple momentum tower, another idea from the book. I had two 20 oz bottles filled with water. The kids tied a string between them and then attached two strings with paperclips to the first string, and then stuck modeling clay onto the paperclips. They held the bottles so the string between them was taut and then carefully swung only one of the clay suspensions. Guess what happened to the other clay swing?

Universal Gravitation

Objects in Motion, Chapter 4, The Law of Universal Gravitation.

This chapter brings together Kepler, Galileo, and Newton, especially the first and the last.  I created a review sheet listing their laws we covered next to a picture of each of them.

All I used for this class was a white board.  I read and we discussed, using the board to draw illustrations and to write equations.  It served as a good opportunity for review as well as an opportunity to consider the information in novel circumstances.

We considered and discussed the weakness of gravity, elliptical motion, "falling around" earth, wobbling planets, Newton's cannon, and satellite rockets.  It makes for good conversation...

Laws of Motion

Chapter three of Objects in Motion is Newton's Three Laws of Motion.  I collected several different demonstrations for this class, and thanks to The Happy Scientist, we demonstrated all three with a scale and some hand weights.

I created a worksheet so they could fill in all the different demonstrations we did during class.  I did a demonstration and then read from the book, did another demonstration, and so forth.

The First Law is that of inertia.  I placed a baseball card on top of a glass, and then stacked coins on top of the card.  I asked them to predict what would happen to the coins when I horizontally flicked the card away (they said the coins would fly off everywhere.)  Of course they dropped into the glass, and I let them try it a few times.  I also gave each of them some thick paper (bookmarks, actually) and a stack of pennies.  I instructed them to place the bookmark on the edge of the table so half of it was off of it and then to put a stack of coins on the bookmark.  They quickly pulled the bookmark out from under the coins and the stack remained intact on the table.  (The boys, of course, experimented with ways to make the coins spill...)

Another demonstration we did used a wheeled cart and a stuffed animal.  Shoving the cart made the toy fall off the back; stopping the cart suddenly made the toy fall forward.  We discussed the usefulness of seatbelts.

Finally, we wrapped up with The Happy Scientist: Newton's Laws that demonstrates all three laws in one activity.  You do not need a subscription to view this particular file, but I highly recommend it.  For $20 a year you get a wealth of videos, experiments, and science information.  Robert Krampf does a great job, and many of his videos are quite funny as well as interesting and informative.  All you need is a bathroom scale--the type with an analog display (digital won't work)--and a heavy object (hand weights work well.)  The kids are fascinated with how the scale changes as the weights are rapidly pushed up or pulled down.  Simple yet impressive!

Towers and Parachutes

Week 3 introduces us to the famous legend of Galileo dropping objects from the Tower of Pisa.  We completed the student exploration guide of the ExploreLearing Free Fall Tower Gizmo.  Another free tower simulator, Galileo Drops the Ball, and many other science simulators are available from SEED.

Before starting the Gizmo I gave a simple demonstration.  I took a feather and a ball and asked which would fall faster; then I dropped a small toy and a large toy.  Some were surprised that the second set of objects hit the ground simultaneously.  Next I dropped a book and a sheet of paper, and they fell at different rates.  Finally, I placed the sheet of paper on top of the book and dropped them; they fell at the same rate.  That got them thinking about concepts that they could explore further with the Gizmo.

After learning about air resistance, terminal velocity, and vacuums, I gave the 3 physics groups a challenge.  They each needed to build an egg parachute that met two criteria.  First, the egg had to fall without breaking; second it had to fall more slowly than a rock dropped simultaneously.

Each of the three groups were all successful, and had very different designs.  The older boys used a large sheet of newsprint for the parachute and a thick cardboard cone to hold the egg.  It's a good thing it didn't rain that day...

The girls covered fabric with lamination, adding in straw stays for the parachute and along the strings; they had a foam cube for the harness, decorated with flowers.  It fell the fasted of the three, but still slower than the rock.

The younger boys used a trash bag for a parachute and a cut up egg carton for the harness, with a good amount of duct tape to hold it all together.

I gave them two weeks for construction.  The day of the drop was very windy.  All the kids (21 of them) gathered for the event.  You can see the videos of each parachute being dropped out a window, a team member dropping the parachute and an adult dropping a rock.

Pendulums

Our third week of co-op we performed the pendulum experiment described in the book.  We had three fishing weights (labeled 1, 2, and 3), three lengths of string, and a stopwatch. I created a data sheet (link goes to Google Docs) for them to fill in; they will need three of them to record data for the entire experiment.

This is one experiment in which the kids are very much surprised by the results.  They expected that lifting the weight higher up would increase the time for 10 swings; they also expected a heavier weight to make a difference.  Only the length of the string matters.

Related Gizmos:  Period of a Pendulum and Pendulum Clock

Ellipses

We are working our way through Objects in Motion: Principles in Classical Mechanics by Paul Fleisher. The first lesson is about Kepler's Laws of Planetary Motion.

A key moment for Kepler was when he abandoned circular orbits for elliptical ones, so I designed an activity around ellipses.  I cut a large foam board into quarters, one for each student, and tacked paper to it.  They put two push pins along the horizontal midline of the paper, slipped a string with the ends tied together over it, and drew an ellipse by drawing the string taut with a pencil and circling the push pins.  They moved the pins progressively farther, then closer, and observed what happened to the ellipse.  We discussed how a circle is a special form of an ellipse, just as a square is a special form of a rectangle.

I then discussed Kepler's Second Law and shaded in a pie piece away from the sun and close to the sun.

For the elementary group we skipped the third law.  For the middle school kids I simply wrote the formula and we discussed what it meant, including exponents and proportionality.  They got the fact that distant planets orbit more slowly and related that to the force of gravity.

If you use ExploreLearning Gizmos like we do, there's one on Ellipse and another on Kepler's Laws.

Physics with Secrets of the Universe

This year we are focusing on physics, and I found a great series of books to introduce middle school students to the subject.  I am using it with our co-op as well.  The series is Secrets of the Universe by Paul Fleisher.  Originally published as a single volume, it is now available as 5 slim books, perfect for moving from elementary into middle school science.  We have started with Objects in Motion: Principles of Classical Mechanics.

This series has so much to like about it.  Fleisher explains concepts in a clear manner with informative examples.  He tells the story through the scientists who first discovered the principles bringing an interesting historical perspective.  He intersperses experiments throughout the text rather than as a separate section.  The graphics are simple and of a single color, yet effective.  It really is a pleasure to read!

The other four books in the series are Liquids and Gases: Principles of Fluid Mechanics; Matter and Energy: Principles of Matter and Thermodynamics; Waves: Principles of Light, Electricity, and Magnetism; and Relativity and Quantum Mechanics: Principles of Modern Physics.

Our TORCH co-op is now up to 6 families and 21 children.  I teach 3 sections of physics, one for middle school girls (4 of them), another for middle school boys (4 of them), and another for older elementary boys (3 of them).  I plan to blog more about out experiences soon!