Chemistry Demonstrations

The following demonstrations are quick and easy reactions or processes that can be used to demonstrate some chemical phenomena to children in high school chemistry or science classes. They include some classic reactions and phenomena that have been used over many years in the teaching of chemistry from the earliest years of high school to undergraduate courses in chemistry at university. The ones collected here have been taken from the "Quickies" sections of:

Sperring, T. (1990). ChemDems: Chemistry demonstrations for secondary schools and colleges. Homebush West, NSW: Science Teachers Association of New South Wales.

Contents

Needs

• 250-500mL Florence or conical flask
• 7cm filter paper
• Retort stand, boss head and clamp.

Method

• Fill the flask to overflowing with water.
• Slide the piece of filter paper across the top of the water ensuring that no air bubbles are allowed to form.
• Invert the flask and carefully clamp it upside down in a secluded spot.

Observation

• The air pressure acting upwards (not just downwards as many students think) supports the weight of the water.
• If left undisturbed the water will slowly evaporate and be replaced by air in the flask until the pressure inside the flask exceeds the external air pressure.

#2 AIR PRESSURE II

Needs

• Aluminium "pop top" can with opening sealed with araldite and a hole drilled to fit a rubber stopper..
• Rubber stopper to fit hole in can.
• Tripod, bunsen, gauze.

Method

• Place about 10mL of water in the can and bring to boil.
• After water has boiled in the can for a minute or so, turn off the bunsen and insert the stopper into the hole. Push it in tightly to ensure an efficient seal.
• Allow can to cool undisturbed.

Observation

• Within a minute or so the can will buckle noisily and be crushed by the external air pressure.

#3 AIR PRESSURE III

Needs

• 1 boiled egg (shelled)
• 250 - 500mL conical or Florence flask (with opening slightly smaller then the egg)
• Tripod, bunsen, gauze.

Method

• Heat the "empty" flask for about half a minute.
• Turn off the bunsen and place the egg onto the flask opening so that it seals it (pointy end downwards).

Observation

• As the flask cools the external air pressure will force the egg into the flask.

#4 IODINE PHASE CHANGES

Needs

• Solid iodine crystals
• 500 and 750mL flask
• Stopper or cork
• Bunsen
• Freon or alcohol

Method

• Place several small pieces of iodine in the flask and insert the stopper loosely.
• Shake the flask and listen for the sound of the solid iodine.
• Wave flask into and out of a moderate bunsen flame until iodine can no longer be heard and iodine has sublimed.
• Cool the flask under a stream of cold water.
• Observe the tiny iodine crystals on the walls of the flask.
• Add alcohol (or freon) to dissolve the iodine.

Observation

• Small pieces of iodine sublime to fill the flask with a purple vapour.
• Some iodine may momentarily melt and run along the inside of the glass showing the liquid phase.
• Upon cooling the purple colour is all but removed as the iodine forms fine solid crystals on the glass
• The alcohol dissolves the iodine to form a brown solution (Freon forms a pink-violet solution).
• All phases of a substance-gaseous, liquid, solid and solution can be observed in this sequence.

#5 AMMONIUM CHLORIDE SUBLIMATION

Needs

• Solid ammonium chloride.
• Evaporating basin.
• Tripod and bunsen.

Method

• Heat a small amount (e.g. 3 to 5g) of NH4Cl moderate flame.

Observation

• The solid will sublime and upon cooling in the air, form white wisps of smoke.

#6 SUPERSATURATION I

Needs

• Sodium thiosulfate crystals (hypo)
• 500 - 700mL flask

Method

• Use a gentle flame or a hotplate to heat the crystals gently until they dissolve in their own water of crystallisation. Cover with a small beaker and stand overnight to cool undisturbed.
• If crystals are uncontaminated, a supersaturated solution will be formed.
• Add a crystal of sodium thiosulfate to the cool solution.

Observation

• The clear colourless solution is quickly transformed into a solid, white, opaque mass. Heat is given out.
• Foot warmers in old trains contained crystals of sodium thiosulfate (hypo)

#7 SUPERSATURATION II

Needs

• Sodium sulfate crystals - 100g
• Beakers

Method

• Dissolve 100g of sodium sulfate crystals in 120mL of water in a clean beaker, warming.
• Place the warm solution into 2 separate beakers, cover and cool. Do not disturb.

Observation

• When cool, lift the cover of one beaker and jar or tap the beaker. Crystallisation should occur.
• Add a "seed" crystal of sodium sulfate to the second beaker. Crystallisation begins at once.

#8 SUPERSATURATION III

Needs

• One (or both) of: lead iodide (0.86g), benzoic acid (11.8g)
• 250 - 500mL flasks (or beakers)
• Bunsen, tripod, gauze

Method

• Dissolve the indicated weight of the solid in 200mL of boiling water.
• Allow to cool or use iced water to cool the flask(s).

Observation

• Crystals will form. For PbI2 - yellow leaflets soon appear giving a "golden rain" appearance in the sun. For benzoic acid, fine white crystals appear.

#9 PHYSICAL AND CHEMICAL CHANGES

Needs

• 0.5M copper sulfate
• 0.2M potassium chromate
• Dilute iodine solution (tincture of iodine)
• Beakers or test tubes

Method

• Dilute some iodine/alcohol solution (tincture of iodine) until it is the same colour as 0.2M potassium chromate.
• Mix equal volumes of blue Cu²⁺(aq) and yellow I2(aq) to produce a green mixture - a physical change.
• Mix equal volumes of blue Cu²⁺(aq) and yellow CrO4 ^2- (aq) to produce a mustard coloured precipitate of CuCrO4 ^- a chemical change.

Results

• The physical change produces no new substance - the properties of the mixture (eg colour, solubility) are those of the mixed components.
• The chemical change produces a new substance whose properties (eg. colour, solubility) are different to those of the reagents.

#10 POLARITY OF WATER

Needs

• Tap
• Perspex rod (or glass rod)
• Ebonite rod
• Piece of flannel or wool
• Piece of silk

Method

• Allow water to run from a tap in a thin, continuous stream.
• Charge the perspex (or glass) rod, with a positive charge, by rubbing it with silk.
• Hold the charged rod near the stream of water.
• Charge the ebonite rod, with a negative charge, by rubbing it with wool (or flannel).
• Hold the charged rod near the stream of water.

Results

• In each case the stream of water will be attracted to the rod, as it is a polar liquid.

Variations

• Try polar liquids (e.g. alcohols, acetone) and non-polar liquids (eg. freon, hexane) running from burettes.

#11 MAKING MATCHES

Needs

• Potassium chlorate (0.5g)
• Sulfur (0.5g)
• Laboratory mat
• Long taper

Method

• With care, crush some KC1O3 with a clean spatula to remove any lumps. DO NOT GRIND!
• Gently mix some sulfur with the KC1O3 in a dry test tube by shaking.
• When homogeneous, pour the mixture onto a laboratory mat.
• Ignite with a taper held at arm's length.

Results

• The mixture will flare as it ignites.
• Match heads contain KC1O3 and antimony trisulfide (Sb2S3).

#12 BOILING BY COOLING

Needs

• Florence or round bottom flask
• Retort ring and stand
• Ice
• Rubber stopper to fit flask
• Bunsen, tripod, gauze

Method

• Half fill the flask with water (coloured with food dye or methylenne blue indicator if desired) and boil it for a minute.
• When water ceases boiling, place the stopper loosely in the mouth of the flask to enable internal pressure to equal atmospheric pressure, then insert the stopper firmly.
• Invert the flask and stand in a retort ring (or clamp it).
• Place a block of ice on the flask (or cool it with wet palm of the hands after allowing it to cool a little).

Results

• The water in the flask will boil.

#13 BOILING BY SUCTION

Needs

• Side arm flask (or test tube)
• Vacuum pump (eg water aspirator)
• Ether (or acetone or methanol)
• Stopper for flask

Method

• Place some of the ether in the flask and firmly stopper it (if acetone or methanol are used it may be necessary to slightly warm the flask on a hotplate).
• Attach to the pump and evacuate.

Results

• The liquid should bubble ie boil.

#14 THE TRICOLOUR

Needs

• 1M ammonia
• Phenolphthalein (or alizarin red or phenol red) indicator
• Saturated lead nitrate
• Saturated copper sulfate
• Beakers

Method

• Place 5 drops of indicator into beaker 1.
• Place 5-10 drops of saturated Pb(NO3)2 into beaker 2.
• Place 5-10 drops of saturated CuSO4 into beaker 3.
• From the one large flask or beaker, at a height sufficient to give a good mixing, pour about 50-80mL of ammonia.

Results

• Different colours will be produced:
  #1 : Red

  #2 : White

  #3 : Blue

Variation

• Include a beaker containing 5-10 drops of a saturated solution of Fe2+ to produce a dark blue-greenish solution.
• Include a beaker containing 5 drops of cresolphthalein indicator to produce a purple solution.

#15 SILVER CRYSTALS I

Needs

• Copper wire
• 0.1M silver nitrate
• Test tube

Method

• Coil a piece of copper wire
• Suspend wire in 0.1M AgNO3 in a darkened place.

Results

• After about an hour crystals of silver will form.
• Leave overnight for longer crystals (and a blue solution).
• Reaction is a displacement reaction:
  • 2Ag⁺ + Cu · Cu²⁺ + 2Ag

#16 SILVER CRYSTALS II

Needs

• 0.1M silver nitrate
• Mercury
• Test tube

Method

• Place a blob of mercury into the test tube and add 5-10mL of 0.1M AgNO3.
• Stand undisturbed in a darkened place for about a day or two.

Results

• Beautiful crystals of silver will grow from the surface of the mercury.

#17 LEAD CRYSTALS

Needs

• Zinc strip (1cm x 8cm)
• 0.1M lead nitrate (or lead acetate)
• Test tube

Method/Results

• As above for "silver crystals 1"
  • Zn + Pb²⁺ · Pb + Zn²⁺

#18 TIN CRYSTALS

Needs

• Iron wire (or nail)
• 0.1M tin chloride
• Test tube

Method/Results

• As above
  • Sn²⁺ + Fe · Sn + Fe²⁺

#19 SUGAR: ENERGY FOOD

Needs

• Powdered sucrose
• Powdered potassium permanganate

Method

• Mix equal amounts (about 5g) of powdered sucrose and KMnO4 in a dry beaker.
• Place mixture on a dry laboratory mat.
• Add several drops of water.

Observation

• The mixture ignites.

#20 MAKING COPPER

Needs

• 0.5M copper II sulfate (or nitrate)
• Zinc powder or iron powder

Method

• Add a spatula amount of zinc (or iron) powder to a test tube full of aqueous copper II ions and shake.

Observation

• The blue colour will be removed from solution.
• Reddish copper powder will form as a sediment and the solution will get warm

#21 CHEMICAL v PHYSICAL CHANGE

Needs

• Sucrose (about 5g)
• Naphthalene (or mothball) or menthol (about 1g)

Method

• Heat each solid separately in a test tube fitted with a 10cm piece of glass tubing.

Observation

• The sucrose chars (forming carbon) and releases steam - a chemical change which does not spontaneously reverse on cooling.
• The naphthalene melts and then boils producing a noticeable odour - a physical change which is reversed on cooling (note crystals in tube).

Alternatively

• Heat solids in evaporating basins with inverted funnel standing on basin.

#22 QUICK DECOMPOSITIONS

Needs

• One (or more) of: sucrose, lead nitrate, copper carbonate, mercury (II) oxide
• Test tubes, bunsen

Method

• Heat a small amount of the solid strongly. Heat the lead nitrate and mercury oxide in fume cupboard,
• Decomposition will occur.

Observation

• For sucrose: black C, steam.
• For Pb(NO3)2: brown NO2, orange PbO
• For CuCO3: black CuO, invisible CO2.

#23 SEPARATION BY ADSORPTION

Needs

• Activated charcoal (about 5 -10g)
• Solution of methylene blue (or methyl violet)
• Conical flask (250 -500mL)
• Filtration apparatus

Method

• Shake 1 -2 teaspoons of activated charcoal with about 150mL of solution containing 2-3 drops of the dye for at least 1 minute.
• Filter.

Observation

• Filtrate will be clear and colourless.

Variations

• Decolourise coloured soft drinks (e.g. Orange, Green Lime or Cola) or brown vinegar using 2 -3 teaspoons of activated charcoal (shake well).

#24 COMBUSTION OF IRON (STEEL WOOL)

Needs

• Piece of steel wool
• Metal tongs
• Bunsen
• Gas jar of oxygen (optional)

Method

• Tease out a handful of steel wool to about a 10cm length, separating the strands as much as possible.
• Hold in a bunsen flame in the dark.
• (Optional) - Place into a gas jar of oxygen.

Observation

• The steel wool burns giving off sparks and forming black iron oxide.
• In pure oxygen a shower of sparks is produced.

#25 COMBUSTION OF SULFUR

Needs

• Fume cupboard
• Sulfur powder (about 1 - 2g)
• Deflagrating spoon
• Gas jar of oxygen
• (Optional) - Universal indicator, a flower, acidified KMnO4

Method

• Fill the end of the deflagrating spoon with sulfur.
• Heat the sulfur until it melts and starts to burn - in fume cupboard.
• Place burning sulfur into oxygen in dark room.

Observation

• The sulfur burns with a bright blue flame.
• Fumes of sulfur dioxide are produced.

Optional

• Test SO2 with a solution of indicator (acidic colour forms).
• Place a flower or coloured fabric in the SO2 (it bleaches).
• Pour a dark pink solution of acidified KMnO4 into the SO2 (colour disappears).

#26 COMBUSTION OF RED PHOSPHORUS

Needs

• Red phosphorus
• Deflagrating spoon
• Gas jar of oxygen
• (Optional) - universal indicator

Method

• As for sulfur.

Observation

• A brilliant white flame is produced.
• Phosphorus pentoxide as acidic.

#27 AN ELECTRIC LEMON

Needs

• Lemon
• Galvanised roofing nail
• Copper nail
• Leads with alligator clips
• Volmeter

Method

• Soften the lemon by squeezing (to break internal membranes).
• Connect the nails to the poles of a voltmeter (galvanised to negative; copper to positive).
• Insert nails into lemon.

Result

• A current should be measurable.

#28 CHALK CHROMATOGRAM

Needs

• Piece(s) of white chalk
• Food dye or dark coloured ink
• Beaker, watch glass (or Gladwrap)
• Methylated spirits or absolute alcohol or Iso-propanol.

Method

• Place an intense spot of an ink or dye about lcm from the base of a piece of chalk.
• Place a 0.5cm depth of the alcohol into a beaker.
• Stand chalk in beaker and cover with a large beaker.

Results

• Coloured spot(s) will move up chalk and separate slowly.

#29 IODINE FORMATION

Needs

• 0.1M potassium iodide
• 0.1M sodium persulfate (or peroxydisulfate) - Na2S2O8
• 1% starch solution
• Beakers

Method

• Mix equal volumes of I-(aq) and S2O8 ^2- (aq).
• Mix equal volumes of I-(aq) and S2O8 ^2- (aq) with a small amount of starch indicator.
• Observe each against white background.

Results

• Iodine slowly forms - in beaker #1 the colourless reactants gradually produce a pale yellow solution which slowly darkens to form a brown solution; in beaker #2 the colour change is noticed sooner as blue iodine-starch complex appears and gradually darkens to give a black colour.
• Reaction is:
  • 2I- + S2O8 ^2- · I2 + 2SO4 ^2-
• For a slower reaction try 0.05M I- and 0.02M S2O8 ^2-

#30 COLLOIDAL SULFUR

Needs

• 0.1M sodium thiosulfate
• 1M sulfuric acid
• Black background
• Test tubes or beakers

Method

• Mix 20mL with 2mL of acid and observe against a dark background.
• Repeat using 1M acid diluted successively to 0.5M, 0.25M, 0.1M.

Results

• A white/pale yellow colloidal precipitate of sulfur gradually forms.
• Rate of sulfur production decreases with acid concentration.
• Reaction is:
  • S2O3^2- + 2H⁺ · S + SO2 + H2O

#31 PEROXIDE DECOMPOSITION

Needs

• 30% hydrogen peroxide (i.e. "100 volume")
• Potassium iodide - 1g
• Measuring cylinder
• Detergent or shampoo

Method

• Place about 20mL of H2O2 and 1mL of detergent into a measuring cylinder in a trough.
• Add about 1g of KI.

Result

• The mixture effervesces vigorously producing a foam which should overflow the container.
• The steps in the reaction are:
  • H2O2 + I^- · H2O + IO ^-
  • H2O2 + IO ^- · H2O + O2 + I ^-

#32 BLEACH DECOMPOSITION

Needs

• Laundry bleach (chlorine bleach)
• Cobalt (II) chloride - 5g (or cobalt II nitrate).
• Flask

Method

• Add about 5g of CoCl2 to about 100mL of bleach and swirl.

Result

• The mixture will effervesce, producing oxygen gas:
  • 2ClO ^- · O2 + 2Cl ^-
• The black precipitate which forms is the unstable CO2O3.
• Co(NO3)2 can be used instead of cobalt (II) chloride.

#33 INSTANT SOLID

Needs

• Saturated calcium chloride solution
• 4M sulfuric acid

Method

• Quickly mix equal volumes of the two solutions against a dark background.

Observation

• The two clear and colourless liquids form a thick precipitate of calcium sulfate which solidifies in the test-tube (or beaker), forming a gel.

#34 SALT "GLUE"

Needs

• A small block of ice
• Beaker of water
• Salt (NaCl)
• Piece of cotton/wool thread or string

Method

• Moisten one end of thread and lie it across block of ice floating on some water.
• Place moist thread across the ice and sprinkle it with salt.
• Wait for a moment and then pull thread.

Results

• Thread will be attached to ice, which can be lifted from beaker.

#35 CASEIN PRECIPITATION

Needs

• 100mL milk
• Vinegar, bunsen, gauze
• Formalin

Method

• Warm 100mL of milk to about 50°C and add acetic acid or vinegar until all the casein has been coagulated.
• Remove the casein and work with fingers until it forms a rubbery mass.
• Soak the casein overnight in formalin.

Results

• Casein, a protein polymer, is coagulated by acid and will harden in formalin to form a rigid plastic.

#36 UREA-FORMALDEHYDE RESIN

Needs

• Urea (about 5g)
• Formalin (about 10mL)
• Test tube
• Concentrated sulfuric acid
• 2L beaker or fume cupboard.

Method

• Stir 5g of urea with 10mL of formalin until a saturated solution is formed.
• Add 1 - 2 drops of concentrated sulfuric acid. Cover with large beaker or do in fume cupboard (formalin gives of acrid fumes)

Results

• The mixture suddenly hardens to form a crosslinked, thermosetting plastic.

#37 SELECTIVE ADSORPTION

Needs

• Kaolin
• One of: methylenne blue, methyl violet, crystal violet
• One of: methyl orange, tartrazine (food dye-102) cochineal (food dye-120)

Method

• Prepare a solution of any two dyes, one from each group above (eg. methylenne blue + cochineal).
• Add a teaspoon of kaolin, shake well, and allow to stand. Add an electrolyte (eg 1% alum solution) to hasten settling.

Result

• Kaolin will absorb some dyes (eg. first group) but not others (eg. second group).
• The colour of the solution will change as a result of the selective absorption of one of the dyes.

#38 RELATIVE DENSITY

Needs

• Methylated spirit
• Olive (or vegetable) oil
• Sudan III dye (optional)
• Measuring cylinder (100 - 250mL)

Method

• Half fill the cylinder with water.
• Carefully pour a layer of methylated spirits onto the water layer.
• Add several crystals of sudan III (or any oil-soluble dye) to about 10mL of a vegetable oil to colour it.
• Add 0.5mL of coloured oil to the measuring cylinder.

Result

• The coloured oil will be suspended at the (invisible) interface of the alcohol and water.

#39 WOHLER'S SYNTHESIS REVERSED

Needs

• Urea (100mL of 1M solution).
• Silver nitrate solution (0.1M)
• Conductivity apparatus (6V battery, electrodes, light bulb or ammeter)
• Beakers

Method

• Test 1M urea for conductivity (non-electrolyte).
• Test 1M urea for ions, with several drops of Ag+ (no precipitate therefore no ions).
• Boil 50mL of 1M urea for several minutes and repeat tests.

Result

• Boiled "urea" is an electrolyte (conducts a current) and forms a precipitate with Ag+.
• Whereas Wohler synthesised urea from ammonium cyanate, the reaction has been reversed:
  • NH2-CO-NH2 Ú NH4 ⁺ + OCN^-
  • Ag⁺ + OCN^- · AgOCN

#40 A QUICK SAPONIFICATION

Needs

• Methyl salicylate (oil of wintergreen)
• 2M sodium hydroxide
• Beakers/test tubes

Method

• Pour 2M NaOH, with stirring, into methyl salicylate.

Results

• A thick white solid (sodium salicylate) is formed by saponification.
  • HOC6H4COOCH3 + NaOH · HOC6H4COO^-Na⁺ + CH3OH

#41 BURNT BACON AND UNSATURATION

Needs

• Strip of bacon
• Metal tongs
• Flask/gas jar of bromine gas
• Bunsen

Method

• Cook the strip of bacon in a bunsen flame to a slight crisp.
• Place bacon in bromine flask and shake.

Results

• Bromine colour is removed rapidly.
• Cooking bacon converts glycerol to acrolein (propenol):

•  
• Bromine reacts with double bonds in acrolein:

#42 FREE RADICAL SUBSTITUTION

Needs

• Overhead projector
• Bromine (liquid)
• Hexane (or cyclohexane)
• Beakers
• Laboratory square
• Blue litmus paper

Method

• Dissolve bromine in the alkane to get an orange colour.
• Place equal amounts of alkane/Br2 solution in beakers upon overhead stage.
• Place laboratory square under one of the beakers (control).
• Turn on OHP.

Result

• Bromine colour is removed from beaker exposed to light.
• Fumes of HBr are visible and can be tested with damp blue litmus paper.
  • C6H6 + Br2 · C6H5Br + HBr

#43 SULFUR SHOWER

Needs

• Sulfur powder
• Large beaker of water
• Dishwashing detergent

Method

• Cover the surface of a beaker of water with fine sulfur powder.
• Add a drop of detergent.

Result

• The sulfur particles cascade to the bottom of the beaker (as the detergent reduces the surface tension).

#44 RAINBOW TITRATION

Needs

• 50mL saturated boric acid solution
• 2M sodium hydroxide
• Universal indicator
• Burette, 2 x 250mL beakers
• Magnetic stirrer

Method

• Colour the boric acid solution with sufficient universal indicator to give a definite reddish colour and set it on a magnetic stirrer beneath a burette.
• Make a colour standard/control by adding universal indicator to a similar volume of water in another beaker, and then adding enough 2M hydrochloric acid to produce a colour identical to that of the boric acid.
• Progressively add sodium hydroxide solution to the acid.

Result

• The colour of the solution should progressively change through the full rainbow of colours as the boric acid is neutralised.
  • H3BO3 + NaOH Ú NaH2BO3 + H2O

Course Outline

Enquiries/Comments to: A.Sperring@mackie.edfac.usyd.edu.au