More Demos 29-32

 
 

Demo 29         Iceberg 

         

Materials:  Denatured alcohol (not rubbing alcohol), ice cube, water, clear glasses or plastic cups (2)

Precautions:  Wear goggles.  Denatured alcohol is poisonous to drink.  It is flammable.  Read product label.

Disposal:  Take the ice cube out and the denatured alcohol can be saved and used a few more times.  It can be flushed down the drain. 

Procedure:  Fill the one glass with denatured alcohol and the other glass with water.  Add an ice cube to the glass with water first.  The ice floats on of the water as an iceberg does in the ocean.  Then add another ice cube to the denatured alcohol and watch it sink to the bottom.

Explanation:  The density of ice is lower than the density of water and therefore floats on water.  The density of ice is higher than that of denatured alcohol and therefore sinks in it.  (Water at 0oC = 1.000 g/cm3, ice at 0oC = 0.917 g/cm3, denatured alcohol at 0oC = 0.810 g/cm3)

   

Demo 30         Ice, Water, And Fire       

 

(Video Link)

Materials:  Coleman® camp appliance liquid fuel. ice cube, water, matches, wine glass

Precautions:  Wear goggles.  Read product label.  Be careful not to knock over the glass with burning fuel.  Have a fire extinguisher near by.

Disposal:  Let the liquid fuel burn out before disposing the water down the drain.

Procedure:  Put one tsp of liquid fuel into the wine glass.   Fill the glass nearly to the rim with water.  Add an ice cube.  Then put a lighted match to the surface of the liquid in the glass, and watch the mixture catch fire.

Explanation:  This demonstration applies the principles of  solubility and density.  The liquid fuel is a non-polar hydrocarbon and therefore does not mix with water and ice.  The ice and liquid fuel both have lower density than water and therefore float on top.    When a lighted match is brought to the top of the liquid, the hydrocarbon vapor ignites.  This is why pouring water over burning oil is a bad idea.

 

Demo 31        Ice Fishing     

 
Materials:  salt, ice cube, water, cotton string 6 inches long, pencil, dish
Precautions:  Be careful not to break the dish.

Disposal:  salt and ice cube can go down the drain

Procedure:  Put the ice cube in the dish. Tie one end of the string to one end of the pencil.  Wet the other end of the string and place it on the surface of the ice cube.  Sprinkle some salt over the ice cube surface where the string is in contact.  Wait 15 to 20 seconds and lift the pencil up like a fishing rod; the ice cube is the fish.

Explanation:  Dissolving salt and other substances, such as alcohol and antifreeze, will make water freeze at a temperature lower than the normal freezing temperature of 32o F (0oC).  As the salt dissolves on the surface of the ice, the ice melts to form a thin film of water.  When the ice cub melts it takes heat away from the immediate surrounding causing the thin film of ice water on the surface of the ice cube and on the string to freeze at a lower temperature and that causing the string to stick to the ice cube.  Salt is added to ice in churning homemade ice cream in order to get a temperature lower than 32o F to freeze the ice cream mix.

 

Demo 32           Cartesian Diver        

 
 Materials:  clear soft plastic bottle such as a 2-liter soft drink bottle with cap, medicine dropper, water

Precautions:  None.

Disposal:  Pour water down the drain.

Procedure:  Fill the plastic bottle to the top with water.  Suck some water into the medicine dropper to about half full.  Drop the medicine dropper into the bottle of water, and cap it tightly.  Now squeeze the bottle and watch the dropper dive down to the bottom.  Release your squeeze and watch the diver come up.  If it does not work very well, squeeze it harder.  If that still does not work try adjusting the amount of water inside the medicine dropper.

Explanation:  Volume of a gas decreases under pressure – known as the Boyle’s Law.  The air inside the medicine dropper is compressed by the water pushed into the medicine dropper as you squeeze the bottle.  More water in the dropper makes it heavier and therefore, it sinks.  As you release the pressure, the air expands and forces the water out of the dropper making it lighter, and it rises.