Chemistry/Chem 11 Demos
- 1 FIRE WRITING
- 2 INVISIBLE INK MESSAGE
- 3 POP BOTTLE CANNON
- 4 A SIMULATED “ACID IN YOUR EYE” ACCIDENT
- 5 WHY WORRY ABOUT SAFETY?
- 6 INDICATOR SPONGE
- 7 U–TUBE WITH UNEQUAL ARMS
- 8 THE MYSTERIOUS SUNKEN ICE CUBE
- Introductory demonstration 1
- Large sheet of porous (non–coated) paper to make a “WELCOME” sign
- Cotton swab
- Tape (to suspend paper from blackboard)
- Wooden splint
- 100 mL of saturated potassium nitrate (KNO3)
Wet a cotton swab with potassium nitrate and use the swab to write ”WELCOME” on the paper. The letters must be continuous and at least 3/8” wide. Allow the paper to dry thoroughly. On the day of the demonstration, suspend the paper from a blackboard with tape. Touch a glowing hot wooden splint to the start of the message. The message will be traced out by the glowing paper.
INVISIBLE INK MESSAGE
- Introductory demonstration 2
- long sheet of absorbent paper
- large piece of cardboard (larger than the sheet of paper)
- adhesive tape
- 2 – atomizer spray bottles
- paint brush (1/2” to 1” wide)
- 3 – large beakers
- 10 g of ferric chloride
- 2 g of ammonium thiocyanate
- 5 g of potassium ferrocyanide (CARE: not ferricyanide)
Dissolve 10 g of ferric chloride in 200 mL of water. Use this solution to paint a welcoming message such as “ CHEMISTRY RULES!” on the paper, in such a way that “CHEMISTRY” is separated from “RULES!” by at least 8–10 inches, and allow to dry overnight. Using adhesive tape, attach the paper to the large sheet of cardboard to act as a stiff backing.
Dissolve 2 g of ammonium thiocyanate in 200 mL of water and put into one atomizer. Dissolve 5 g of potassium ferrocyanide in 200 mL of water and put into the second atomizer. Spray the left side of the message with potassium ferrocyanide to reveal the word “CHEMISTRY” in dark blue. Spray the right side of the message with ammonium thiocyanate to reveal the word “RULES!” in blood–red colour.
POP BOTTLE CANNON
- Introductory demonstration 3
- 750 mL plastic pop bottle (no bigger!)
- 10 cm x 10 cm square of aluminum foil
- rubber stopper to fit bottle
- tesla coil
Roll up the aluminum foil into a tube and insert into the pop bottle. Add about 5 mL of methanol to the bottle, stopper and shake a few times. Turn on the tesla coil and let a spark jump from the tip of the coil to the piece of aluminum foil inside the bottle. A satisfying explosion will bounce the rubber stopper off the ceiling.
Use this to get the attention of the class on the first day. Three such bottles make a “three gun salute” to welcome students to Chemistry 11.
The methanol vapour and oxygen form an explosive mixture which is ignited by the spark. Before you decide to make it “bigger and better” you should know that adding pure oxygen to the bottle gives a blast which is almost deafening and is strongly advised against because it shreds the bottle into fragments which can cut students standing 20 feet away.
A SIMULATED “ACID IN YOUR EYE” ACCIDENT
- The need for safety goggles
- Large petri plate
- Overhead projector
- Permanent marker (black preferred)
- Dropping pipet
- 6 M HCl (hydrochloric acid)
- Raw egg (white only)
- 50 mL of saturated NaHCO3 (sodium bicarbonate)
Draw a large eye on the bottom of the petri plate, place the petri plate on the overhead projector and place the egg white in the petri plate. [Both egg white and the eye’s pupil are protein gels.] Place several drops of acid on the egg white; it instantly becomes opaque. Adding some baking soda neutralizes the acid but does not undo the damage to the egg white. NaOH solutions work the same way but the opaque area continues to expand for several hours!
WHY WORRY ABOUT SAFETY?
- Working with dangerous chemicals
- 1 L flask, with a stand and clamp to hold the flask
- one hole stopper to fit flask, fitted with a glass tube and rubber tubing
- 1 L graduated cylinder and 40 cm of 6-8 mm OD glass tubing
- 100 mL graduated cylinder (for nitric acid)
- safety goggles
- 60 mL concentrated nitric acid
Almost fill the 1 L graduated cylinder with water and place the 40 cm glass tube into the cylinder. The 40 cm glass tube should go to the bottom of the 1 L graduated cylinder when connected to the rubber tubing leading to the flask. Set up the stand and clamp so the flask can be supported vertically while allowing the rubber tubing to connect to the glass tube in the graduated cylinder.
[Read the following to the class. Tell them that they must record all their observations.]
Ira Remsen was a 19th century chemist who recorded his observations on the first experiment he ever did, before he had learned anything about safety in the Chemistry laboratory. He wrote
[Hold up a copper penny]
[Put on goggles and hold up a stock bottle of concentrated nitric acid. Read some of the warnings on the side.]
[Explain that for safety reasons you are doing the experiment a bit differently than Remsen did. Remove the stopper and pour about 60 mL of acid into the flask. Tilt the flask and slide in the penny. Replace the stopper and clamp the flask in place. Allow 4-5 students at a time to get a closer look. After a couple of minutes, continue reading.]
[When the reaction has stopped, ask one student to describe the penny – its gone – and have students hypothesize where it went. After 5–10 minutes another observation is made: the water travels up the glass tube and into the flask. The resulting solution in the flask is turquoise blue and the brown gas in the flask fades.]
- The need for clean work benches
- Cellulose sponge
- Rubber gloves
- Large container to hold sponge and solution
- 1 g of congo red indicator
- 100 mL distilled water
- 100 mL of 1 M acetic acid
- 100 mL of saturated sodium hydrogen carbonate (about 10 g / 100 mL)
Dissolve about 1 g of congo red in about 100 mL of distilled water. Soak the sponge with the congo red solution and ring out the sponge using rubber gloves. Let the sponge sit in the liquid overnight, squeeze out the liquid and allow to dry completely. Rinse with fresh water a few times and the sponge is ready for use.
Students are often careless about cleaning up their benches, especially at the start of the year. Clean up a little 1 M acetic acid and saturated sodium hydrogen carbonate from the bench to show students what happens when the sponge is used to clean up acidic or basic solutions.
U–TUBE WITH UNEQUAL ARMS
- Density of water vs alcohol
- Big U-tube (14–18 mm glass tubing or 1/2” tygon tubing, about 18 in high)
- stand and 2 clamps
- ethanol or methanol
Clamp the U–tube with the bend downward. Fill the tube about 1/2 full of water and then carefully, so as to minimize mixing, pour alcohol into one side arm until the tube is almost full. The result will be a U–tube having liquid at a higher level on one side than on the other.
Demonstrate that there is no blockage by gently blowing into one side arm and showing that the liquid can move freely.
What is Happening:
Normally, a U-tube has liquid at the same height in each arm because the mass of the liquid in each arm pushes down equally (otherwise the liquid would move) and therefore requires equal heights of liquids. The alcohol has a lower density than the water and therefore a greater volume of alcohol is required to have the same mass as a lesser amount of water. Hence, more alcohol must “pile up” to equal the downward push of the smaller amount of water.
THE MYSTERIOUS SUNKEN ICE CUBE
- Density of ice vs water or alcohol
- 2 – 250 mL beakers
- two ice cubes
- 500 mL of ethanol or methanol
- 500 mL of distilled water
Half–fill one beaker with alcohol and half–fill the other with distilled water before presenting the beakers to the class. Have a student drop one ice cube into each beaker.
The ice in water floats (density of ice = 0.9 g/mL, density of water = 1.0 g/mL) whereas the ice in alcohol sinks (density of alcohol = 0.79 g/mL). Ask students to explain what must be happening.