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Suggests a benchtop piece that will probably need an audio/visual aid to be seen by the audience.

Incompressibility of Water

What it shows

The bulk modulus of water is about 2.2 x 109 Pa, which means that a change of 1 N/m2 of external pressure on the liquid is able to change a given volume of it by a factor of 4.5 x 10-10 (for comparison, the same pressure change would produce a volume change of about 7 x 10-6 for air and 7 x 10-12 for cast steel ). So if we can completely fill a Florence flask with water, we can use it as a hammer to drive a nail into a board!

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Coke Can Buoyancy

What it shows

An unopened can of Diet Coke floats in a tank of water, whereas the same cannot be said for a can of regular Coca-Cola.

photo of fish tank with can of diet coke floating in it

Setting it up

Use the smallest available tank. If unopened cans are not already in the Prep Room, they can be procured...

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Buoyant Force on Finger

What it shows

An object does not need to float in order to experience the buoyant force.

finger about to push against liquid in a cup

In this example we see a cup of water at rest on a pan balance. When the demonstrator pushes a finger down into the liquid, the buoyant force of the liquid pushes...

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Bean Buoyancy

What it shows

Objects with a density lower than the fluid that they are submerged in will float; objects with a greater density will sink. This is shown using a brass ball and ping-pong ball of equal size, and a sea of beans.

How it works

500g of navy beans form a rather coarse fluid in a 1.5L glass beaker. Embedded in the beans is a ping pong ball, and sitting on the surface is a brass ball, 4cm in diameter. This fluid needs to have flow 'induced', and this is done by shaking the beaker side to side. The ratio of densities of brass:beans:ping-pong is approximately...

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Viscous Flow of Bread Dough

Bread dough is stiff but still flows. A big blob of foodstuff that slumps over time, like Silly Putty but large and edible.

Make bread dough enough for a couple loaves, and knead it stiff enough that a round ball of dough takes half an hour to slump to half its original height. Place on a plate, put a camera on it. Project the image at the beginning, just as the dough ball is released, and again some time later, after viscous flow.

Potato Chip Calorimeter

A soda can with 50 ml of water is held over a burning potato chip of known mass. A thermocouple reads the temperature of the water, and its change, to estimate the energy content of the chip.

Other burnable foods include nuts, e.g. brazil nut, and other kinds of fried snack chips.

The heat transfer from burning chip to soda can bottom is only so good, and the temperature rise does not match that expected in the ideal case.

Ice in Water and Ethanol

Ice in water at 0°C is strained and added to a room temperature, 50% ethanol in water mixture. Stirred with a temperature probe, the iced mixture reaches -2°C. 

The stainless steel temperature probe is connected to a Vernier Labquest Mini and LoggerPro software displays a record of the temperature.  Two probes can be used, one in the ice water, and one in the room temperature alcohol. 

Instead of beakers, thick walled pint glasses are used. A strainer and bowl are needed for straining the ice from the water, showing that the same ice melting in water at 0°C...

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Mixing Ethanol and Water

Ethanol and water are mixed in volumetric glassware, showing a volume decrease and a temperature increase.

Two 250 ml graduated cylinders are filled to the line with water and ethanol (100%). A temperature probe shows both at room temperature. The temperature probe is then moved to an empty 500 ml graduated cylinder, and the contents of the two smaller cylinders poured simultaneously to mix well. 

The temperature of the mixture rises about 8°C, and the volume decreases to 480 ml just after mixing, clearly visible on the scale of the 500 ml cylinder, and to the class by...

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Nitrogen Phase Change

Liquid nitrogen is pumped on and freezes into a sponge of solid nitrogen.

The liquid nitrogen is in a 600 or 800 ml beaker under a shielded bell jar on top of the red vacuum cart. A cold trap is not necessary if only nitrogen is being pumped on.

It is important that the beaker of liquid nitrogen not have frozen water vapor on its side, as the view is impaired. A camera is zoomed in on the beaker, which is in a thick glass bell jar and an acrylic tube shield.

With the pump running and the bell jar vent open, pour the nitrogen and cover the beaker with bell jar. Open up...

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Vacuum Infusion

A vacuum is drawn over a beaker of sliced cucumber covered in a clear dressing. The cucumber outgases, making bubbles. When the atmosphere is readmitted, the dressing is forced into the cucumber, rendering it translucent and seasoned. 

A polycarbonate bell jar with a volume of about three liters is centered on the base, with attention to the seal. The vacuum pump tube ID is the same as the outlet tube OD, so attach by hand. Vacuum release by sliding the vinyl tube off of the outlet. 

The vacuum pump is the oil-less variety, and is not bothered by water. The pump is...

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Iron Tin Reaction Kinetics

Dark red iron[III] solution is rapidly reduced to colorless iron[II] by addition of tin[II] chloride solution, with the rate depending on concentration and temperature.

Four medium footed cylinders are prepared with 100 ml of ferric chloride solution 0.01M with potassium thiocyanate solution added to make the dark red complex. One of the solutions should be hot, so just the iron and thiocyanate solutions in that cylinder, with a 150ml beaker for the demonstrator to fill with hot water from the water cooler, right before the demonstration.

The cylinders are on the bench top in...

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Reaction of Magnesium and Air

A magnesium ribbon is held with tongs and lit with a match or torch, making a bright flame that consumes the ribbon from the bottom up.

The ribbon should be about 20-30 cm long. Hold the ribbon with the tongs high and at arms length. Let the magnesium ribbon hang at a steep angle but not vertical. Light the bottom of the ribbon by bringing the end of the torch flame up to ribbon.  Magnesium will melt before it lights, so carefully with the torch. The ribbon can also be lit with a wooden match.

Wear safety glasses and don't look directly at the flame.

Hydrogen Peroxide Decomposition by Iodide

Hydrogen peroxide 30% in a large round flask decomposes to boiling water and oxygen when postassium iodide is added.

The 12L Round Bottom Flask is set on white C-Fold towels covering a large cork ring on the lab bench.  100-150 ml of 30% hydrogen peroxide is carefully poured in. The liquid should be visible against the white towels from the perspective of the class, and any camera, if used.

The catalyst is 5 g of potassium iodide in a small plastic weighing boat labeled KI.

Safety goggles and gloves. Raise the projection screen and make sure the flask is...

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Specific Heat of Air and Water

Two clean plastic cups, one filled with room temperature water, the other empty, for a student to test with their finger.

Supported by experience, this is a way to introduce heat capacity as an important variable in measuring temperature.

Make sure the water has been in the room long enough to equilibrate. Cover the water as any evaporation will cool it.

Food safe cups and potable water. And safety glasses, because why not?

Limiting Reagent, Vinegar or Baking Soda?

Vinegar and two different amounts of baking soda in plastic soda bottles with balloons.

Two 500ml PETN soda bottles of the same make, split a bottle of vinegar between them.

11" balloons are pre-inflated with dry air, with care taken not to stretch the neck of the balloon. Into the balloons with a funnel go one, two teaspoons of baking soday. With 250 ml of vinegar, that's like six liters of gas potential if one carbon dioxide comes from one acid hydrogen ion.

Tap the baking soda powder down away from the neck of the balloon. Stretch the neck and place it over the top...

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