Chemistry Class Demonstrations:

    We share these for use by Qualified Science Educators Only. Some have inherent safety problems that must be provided for. We have room for the demonstration outline only. You must assume the responsibility for the safety and success of your own demonstration.

Week 1

Oxidation of alcohol by Mn2O7: danger

  • This demonstration is Potentially Dangerous! Try adding only a few crystals at first (you can always add more if the reaction slows) and do NOT try to stop the reaction!
  • Fasten a large test tube to a ringstand with the clamp at the top of the tube.
  • Pour concentrated sulfuric acid to fill one-fourth of the tube.
  • Slowly add an equal amount of ethyl alcohol. Pour it down the side of the tube with a pipet so that the two liquids do not mix.
  • As a safety precaution, immerse the tube in a large beaker of water to cover at least half of the acid layer.
  • Add a few crystals of potassium permanganate to the tube.
  • In a couple of minutes bubbles of gas begin and a green color forms at the interface of the two liquids. Then sparks are produced that pop and flash.
  • Some comments:
    • Green Mn2O7 forms at the interface.
    • It is a powerful oxidizing agent that oxidizes the alcohol at the interface.
    • In concentrated form, this anhydride of permanganic acid is highly explosive!

  • The reaction complex:

    1. KMnO4 (s) + 3H2SO4 (aq) K+ (aq) + MnO3+ (aq) + H3O+ (aq) + 3HSO4- (aq)

    2. MnO3+ (aq) + MnO4- (aq) Mn2O7 (s)

    3. Mn2O7 (s) + CH3CH2OH (aq) 2CO2 (g) + 3H2O (l) + 4MnO2 (aq)
Week 2

An unstable compound: danger

  • Place about 5 g of iodine crystals in a beaker.
  • Add about 20 ml of concentrated ammonium hydroxide and stir.
  • Filter the solution.
  • The compound on the filter paper is nitrogen triiodide. It SHOULD be stable while wet. After it drys, it WILL EXPLODE loudly when touched or disturbed in any way. Although not a powerful one, this compound is an explosive and should be treated as such.
  • The compound is too unstable to be stored.
  • Time your preparation so the compound will be just dry when needed.
Week 3

Dehydration of sugar by H2SO4: caution

  • Fill a small beaker about one-third with table sugar.
  • Slowly pour about 10 ml of concentrated sulfuric acid over the sugar.
  • Steam and a column of black carbon will begin to rise from the beaker.
  • This reaction produces noxious fumes and should be well vented.
  • The overall reaction: C12H22O11(s) + 11H2SO4(aq) 12C(s) + 11H2SO4 . H2O(g)
Week 4

Stability in atoms: danger

  • Generate CO2 gas in a 1 dm3 covered beaker using baking soda and vinegar.
  • Bring a burning wood splint into the CO2 in the beaker. Observe.
  • Hold a length of magnesium ribbon with tongs and light it.
  • Bring the burning Mg ribbon into the CO2 in the beaker. Observe.

    Results:

  • The wood splint goes out.
  • The burning Mg ribbon becomes more violent in CO2.
    2Mg + CO2 C + 2MgO

    Questions:

  • Write the electron configuration for carbon (wood splint) and magnesium.
  • Which element has its valence electrons closer to the nucleus?
  • Are atoms with electrons closer to the nucleus less reactive than those atoms in which the electrons are farther away from the nucleus?
Week 5

Black and white precipitates:

  • Prepare these two solutions before class:
    1. A 0.1M SnCl2 solution - 19 g SnCl2 in 1 liter of water.
    2. A 0.1M HgCl2 solution - 27.2 g of HgCl2 in 1 liter of water.
  • Add a couple of drops of concentrated HCl to each to prevent unwanted complexes.
  • Pour 10 ml of SnCl2 in beaker 1.
  • Pour 90 ml of HgCl2 in beaker 2.
  • Quickly pour the contents of beaker 2 into beaker 1. Always pour the larger volume into the smaller one.
  • A white precipitate forms.
    2Hg+2(aq) + Sn+2(aq) + Cl-1(aq) Hg2Cl2(s) + Sn+4(aq)
  • Reverse the amounts of chemicals and quickly pour the larger volume into the smaller one.
  • A black precipitate forms.
    HgCl2(aq) + Sn+2(aq) Hg(s) + Sn+4(aq) + 2Cl-1(aq)
Week 6

Rapid oxidation: caution

  • Do this in a hood.
  • Place a spoonful of potassium permanganate in an evaporating dish.
  • Pour about 10 ml of glycerin onto the pile.
  • Smoke and Fire in about 15 seconds.
Week 7

Popcorn mass: caution

  • Lightly coat the inside of a 500 ml beaker with cooking oil. Record the weight of the beaker.
  • Place about 30 kernels of popcorn in the beaker. Record the weight of the beaker and contents.
  • Cover the beaker with a wire screen and heat over a burner flame. Be careful not to burn the popped kernels.
  • After the beaker cools, remove the wire screen and record the mass of the beaker and contents.
  • Compare the mass before and after popping.

    Questions:

  • Does the popcorn gain or lose mass during heating?
  • What is the percentage of mass change?
  • What substance accounts for the change in mass?
Week 8

Change copper to gold - making brass alloy: caution

  • Place about 5 grams of zinc dust in an evaporating dish.
  • Add enough 6M NaOH to cover the zinc and fill the dish one-third full. Six molar NaHO is 240 g per liter.
  • Heat the solution to near boiling.
  • Carefully place a cleaned penny into the mixture.
  • It will take 3 to 4 minutes for the zinc plating to form.
  • Remove the penny, wash it and blot it dry. The copper has now been changed into "silver".
  • Using tweezers, hold the coated penny in a burner flame. The gold color begins to form immediately. After about 5 seconds remove the penny, wash it, and dry it.
  • Zinc reacts with sodium hydroxide to produce sodium zincate, Na2ZnO2, which is then reduced by the copper to metallic zinc. Heating the penny causes a fusion of the zinc and copper.
  • Brass is 60 to 82% Cu and 18 to 40% Zn.
Week 10

Oxygen gas from laundry bleach:caution

  • Set up a gas-collecting apparatus. A filtering flask with a hose connected to the arm is a quick one to use.
  • Put 100 ml of bleach in the flask.
  • Add about 5 g of cobalt (II) chloride.
  • Quickly stopper the flask and swirl the contents.
  • Displace all the air in the flask and collecting tube before collecting the gas by water displacement.
  • The reaction: 2ClO -(aq) CoCl2 catalyst O2 (g) + 2Cl -(aq)
Chlorine gas from laundry bleach: warning
  • Set up a gas-collecting apparatus.
  • Put 30 ml of bleach in the flask.
  • Add 5 ml of 1M HCl and stopper the flask. (stronger acid will generate gas more quickly)
  • Collect the gas by upward displacement of air.
  • The reaction: ClO -(aq) + Cl -(aq) + 2H+(aq) Cl2 (g) + H2O(l)
  • Do not inhale the chloring gas! It can be identified by its color.

  • Why were the two gases (oxygen and chlorine) collected differently?
Week 11

Blue precipitate:

  • Start with about 200 ml of clear, saturated limewater solution.
  • Add a few drops of cobalt chloride solution.
  • Immediately a blue precipitate forms.
    CoCl2(aq) + Ca(OH)2(aq) Ca+2(aq) + 2Cl-1(aq) + Co(OH)2(s)
Week 12

How much is a mole? #1

  • Place 12 grams of animal charcoal (carbon) in a container.
  • "How many molecules are in this container?"

How much is a mole? #2

  • Show students exactly one liter of water.
  • There are 1.4 billion km3 of water on Earth.
  • That is 1.26 X 10 21 liters.
  • While this number is very large, it is much smaller than 6.02 X 10 23.
  • It would require 478 earths to contain one mole of liters of water.
Week 14

A Serial Dilution:

  • Place 3.95 g potassium permanganate into a 250 ml volumetric flask.
  • Add distilled water to the mark.
  • Stir with a magnetic stirrer.
  • Pour into erlinmyer flask #1.
  • Pipet 25 ml of this solution into the volumetric flask.
  • Add distilled water to mark and stir.
  • Pour into flask #2.
  • Pipet 25 ml of this solution into the volumetric flask.
  • Add distilled water to mark and stir.
  • Pour into flask #3.
  • How are these solutions different?
  • Calculate the Molarity of each solution.
Week 15

Displacement of Tin by Zinc: caution

  • Make a solution of SnCl2 by dissolving 20 g in 200 ml of water in a 400 ml beaker.
  • Add 40 ml of concentrated HCl and mix the solution.
  • Cover the bottom of the beaker with mossy zinc.
  • Spongy tin will immediately form and soon rise to the surface.
  • The two reactions involved:
    1. Zn(s) + SnCl2(aq) Sn(s) + ZnCl2(aq)
    2. Zn(s) + 2HCl(aq) H2(g) + ZnCl2(aq)
Week 16

Ammonia Fountain The Ammonia Fountain: caution

  • This demonstration works because of the extreme solubility of ammonia in water.
  • The glass tube extending into the flask has been drawn into a fine tip.
  • The beaker has water, 20 ml of HCl, and litmus indicator.
  • The dropper is filled with water.
  • Fill the flask with ammonia gas by:
    1. Place a spoonful of ammonium chloride and a spoonful of sodium hydroxide in a large DRY test tube.
    2. Gently heat the tube in a hood and direct the ammonia produced into the dry flask.
    3. It is important that the flask be completefully filled with ammonia gas.
    4. The reaction: NH4+ + OH - NH3 + H2O
  • Close the pinch-clamp and stopper the flask.
  • Place the flask on the ringstand with the end of the tube just above the bottom of the beaker.
  • To begin, remove the pinch-clamp and squirt the water from the dropper into the flask.
  • The vacuum caused from the dissolving of the ammonia gas will cause a fountain of water to be sprayed into the flask.
  • The red solution in the beaker will become blue as it enters the flask.
  • For the fountain to work, the flask must be completely dry at the start and the flask must be completely filled with ammonia gas.

    Acetylene Production: danger

    • Place 2 or 3 ml of water in a balloon.
    • Push a piece of calcium carbide, CaC2 into the balloon.
    • Tie off the balloon and observe.
    • When expansion stops, tape the balloon to a meter stick and bring it to a flame.
    • Acetylene production: CaC2 + 2H2O Ca(OH)2 + C2H2
    • Burning of acetylene: 2 C2H2 + 5O2 4CO2 + 2H2O + heat
    Week 17

    Double Displacement betweem two solids:

    • Place equal amounts of lead (II) nitrate and potassium iodide in a small flask.
    • Stopper the flask and swirl.
    • The two white solids produce a yellow one.
    • The reaction: Pb(NO3)2(s) + 2KI(s) PbI2(s) + 2KNO3(s)
    • Lead (II) iodide is the yellow solid.

    Other Chemistry Resources:
    Roanoke Valley Governor's School | Chemist's Art Gallery | Lecture Demos, U of Illinois

    The Internet Science Room Chemistry Class | Second Semester Demonstrations