A Demo A Day: Demonstrations and Props Used in My General Chemistry Class

Lists of classroom demonstrations

Classroom demonstrations have long been an approach used to convey information in chemistry courses. The intent is to help student learning by providing physical examples to illustrate concepts described in class. Although I am not suggesting that readers should feel obligated to do the same, it has been my goal to show at least one of these examples per class meeting time in all of my courses. This has been difficult to achieve for every day of a course, but this past fall, every non-exam meeting for my General Chemistry I class had at least one of these types of physical examples. The demonstrations and props used for last fall, and some others used in previous fall semesters, are briefly described below. My motivation for using each example is also described. The demonstrations and props are categorized by their best fit to chapters in the course textbook (Tro, N. J. Chemistry: A Molecular Approach, 2020).1 This seemed to be a good starting point for categorizing the examples, recognizing that many of them fit into multiple categories.

The examples used in the Fall of 2021 are starred (***). The descriptions are rather terse, but some of them might become integrated into future blog posts. Videos describing many of these examples are posted on the YouTube channel Chem Demos. Three examples of the videos are included below. These videos have been organized into categories, along with some discussion-promoting questions, on the .2 

 

Ch1 - Matter, Measurement, and Problem Solving

Ammonia spray welcome sign - Ammonia solution was sprayed onto goldenrod indicator paper marked with the letters “WELCOME” drawn in colorless wax. Where the ammonia spray contacted the paper that was not covered by the wax, it changed from yellow to red. The word “WELCOME” stayed yellow. Spraying the reddened sign with vinegar (acetic acid) turned it back from red to yellow.

This was done to show that the chemistry course can be welcoming and colorful, and to show acids and bases.

***Mask blocks ammonia spray on goldenrod paper - Ammonia solution was sprayed onto goldenrod indicator paper marked with a sick face drawn in colorless wax. Placing a facemask in front of the sprayer kept the droplets of ammonia solution from reaching the goldenrod paper.

This was done to show how masks make it more difficult for COVID to spread and to encourage students to wear their masks.

 

Video 1: Density and Compressibility with a Soy Sauce Packet Cartesian Diver, Chem Demos YouTube Channel, August 1, 2020. (Watch more videos of demos highlighted here on the .2)

 

***Cartesian diver – A bottle was filled completely with water with a soy sauce packet floating at the top of the bottle. When the bottle was squeezed, the air bubble in the packet was compressed and the density of the packet was increased to where it sank. (See video 1)

This was done to show how gases and liquid differ in their compressibility.

***Kinetic energy of falling textbook – A textbook was pushed off a desktop and fell to the floor. It was noted that the potential energy of the stationary textbook was converted to the kinetic energy of motion of the falling textbook.

This was done to show the difference between potential and kinetic energy.

***Density of a textbook – The mass of the course textbook(measured before class) was combined with its length, width, and height (measured in class) to calculate its density. The density of the textbook was compared with that of water to predict whether the textbook would sink or float if it was thrown into a lake.

This was done to supplement density calculations. This also provided a springboard for discussions about error and approximations in measurements, since hardcover textbooks often do not have the same dimensions of their pages as their cover.

Nano-Earth marble – A blue marble with a diameter of approximately 13 mm was shown and was noted as being a billion times smaller than the diameter of the Earth. 

This was done to show how very small nanometer–scale objects are.

Dry ice temperature – Used dry ice as a prop while converting its sublimation temperature between Fahrenheit, Celsius, and Kelvin.

This was done to supplement temperature conversions between different scales.

 

Ch2 - Atoms and Elements

***Gold and silver nanoparticle samples – Showed transparent polydimethylsiloxane elastomer samples with silver nanoparticles added to produce a yellow color, and gold nanoparticles added to produce a red color.

This was done to show that nanoscale structures can have different properties than that of bulk structures.

***3-D periodic table – Showed a periodic table panel produced by Theodore Gray featuring three-dimensional pictures associated with each element.

This was done to show a wide variety of element samples.

***Mole samples of elements – Showed jars each containing a mole of a particular element (e.g. 12.01 g of carbon such as coal).

This was done to show the size scale of moles of samples.

***Metal vs. nonmetal part of desk – Had students place their hand on a metal part (e.g., a leg) of their desk and also on a nonmetal (e.g., wooden or plastic seat or writing surface) of their desk and asked the student to observe which parts felt colder than the others. The metal parts of the desk felt colder than the nonmetal parts because the metal parts conducted heat from their hands more quickly than the nonmetal parts.

This was done to show the difference in thermal conductivity between metals and nonmetals.

***Avogadro’s number written out on a banner – Showed a long strip of paper with the number 602,000,000,000,000,000,000,000 written on it.

This was done to show the large size of Avogadro’s number.

Silicon vs silicone vs silica samples – Showed samples of a hard, grey silicon wafer; rubbery transparent silicone polymer; and hard, transparent quartz crystals (silica).

This was done to show the importance of using nomenclature carefully.

 

Ch3 - Molecules and Compounds

***Mole samples of compounds – Showed jars each containing a mole of a particular compound (e.g. 18.02 mL of water).

This was done to show the size scale of moles of samples.

***Mole samples of sugars – Showed jars each containing a mole of a particular sugar (e.g. glucose vs. sucrose).

This was done to supplement discussions about carbohydrates often having empirical formulae of CH2O.

***Azobenzene sample – Showed a sample of azobenzene.

This was done to supplement discussions about the empirical formula (C6H5N) vs. the molecular formula (C12H10N2) of azobenzene.

***Magnetic periodic table set – Showed a magnetic periodic table set found at a local department store.

This was done to show a publicly available periodic table activity.

***Copper oxide samples – Showed red copper(I) oxide and black copper(II) oxide samples.

This was done to show the importance of using nomenclature carefully.

***Gypsum crystals – Showed a sample of gypsum (calcium sulfate dihydrate)

This was done to show a common hydrate compound (e.g., CaSO4  2 H2O).

Ammonium dichromate sample – Showed a sample of ammonium dichromate.

This was done to supplement balancing the reaction for decomposition of ammonium dichromate.

 

Ch4 - Chemical Reactions and Chemical Quantities

***Dry ice in water with universal indicator – Dry ice was added to water containing universal indicator. The carbon dioxide gas reacted with the water to produce carbonic acid which changed the color of the indicator.

This was done to show some carbon dioxide chemistry.

***Butane lighter – Lit a butane lighter for the class and described the flame. Soot could be collected by holding aluminum foil over the flame.

This was done to illustrate the combustion reaction of butane with oxygen to do stoichiometry calculations. Incomplete combustion/less than 100% yield can be shown by describing the yellow color of the flame from carbon particles, or by collecting the soot on aluminum foil.

Propane torch with low oxygen flow – Lit a propane torch and then gradually blocked the air intake vents, turning the blue flame to a white-tipped flame and then a yellow flame.

This was done to illustrate the combustion reaction of propane with oxygen to do stoichiometry calculations. Incomplete combustion/less than 100% yield can be shown by describing the production of incomplete production products such as carbon monoxide and soot.

Alcohol rocket car – Lit a combination of ethanol and air in a plastic bottle set sideways on wheels.

This was done to illustrate the combustion reaction of ethanol with oxygen to do stoichiometry calculations. Incomplete combustion/less than 100% yield can be shown by describing the production of incomplete production products such as organic acids, aldehydes, etc.

Oxidation-embrittled polyethylene bottle – Squeezed a new, soft polyethylene bottle and an old, brittle polyethylene bottle. The latter shed little microplastic bits.

This was done to show a very incomplete oxidation or combustion reaction. The polyethylene in the bottle was oxidized, but not completely to carbon dioxide, and made the plastic brittle. This is also a good opportunity to discuss microplastics.

***Samples of bromine water and iodine – Showed samples of bromine and iodine in a relatively safe form for passing around a classroom.

This was done to show other diatomic elements besides oxygen and nitrogen gases.

 

Ch5 - Introduction to Solutions and Aqueous Reactions

***Diluting copper(II) solution – Added enough water to a copper(II) solution to double its volume, diluting its concentration by a factor of two. Placed two equal containers with the diluted solution in front of each other, which appeared to have the same color intensity as the undiluted solution.  

This was done to show principles of dilution and the influence of solution concentration on light absorption.

Conductivity of NaCl – Used a conductivity meter to show that sodium chloride solution conducted electricity. Placing the probes on solid sodium chloride would have shown that the solid does not conduct electricity.

This was done to show that dissolved ionic solutions conduct electricity.

***Silver(I) nitrate solution + tap water – Combined silver(I) nitrate solution and tap water to produce solid silver chloride. Explained that silver(I) nitrate solution can be used to check the quality of deionized water.

This was done to show a precipitation reaction.

Aluminum chloride + potassium carbonate - Combined aluminum chloride and potassium carbonate to illustrate the precipitation reaction to produce solid aluminum carbonate and potassium chloride solution.

This was done to show a precipitation reaction.

Copper(II) sulfate + barium chloride - Combined copper(II) sulfate and barium chloride to illustrate the precipitation reaction to produce solid barium sulfate and copper(II) chloride solution.

This was done to show a precipitation reaction.

***Chalk + hydrochloric acid – Placed calcium carbonate chalk into hydrochloric acid to produce carbon dioxide, water, and calcium chloride solution.

This was done to show an acid and base and gas-producing reaction.

Dissolves eggshell on raw egg – Placed a raw egg in vinegar (acetic acid) for a couple of days to dissolve the eggshell and leave a raw egg in its membrane. The calcium carbonate in the shell reacted with the acetic acid to produce carbon dioxide, water, and calcium acetate solution.

This was done to show an acid and base and gas-producing reaction.

Vinegar and baking soda – Placed acetic acid onto sodium hydrogen carbonate to produce carbon dioxide, water, and sodium acetate solution.

This was done to show an acid and base and gas-producing reaction.

 


Video 2: 
Headstones vs acids, Chem Demos YouTube Channel, September 20, 2020 (Watch more videos of demos highlighted here on the .2)

 

***Hydrochloric acid reacts with limestone but not granite - Placed hydrochloric acid onto calcium carbonate limestone to produce carbon dioxide, water, and calcium chloride solution. Granite did not easily react with hydrochloric acid. (See video 2)

This was done to show an acid and base and gas-producing reaction.

Fizzy Skittles – Showed class a type of Skittles candy that had a powder coating that fizzed in the mouth. The product is no longer produced, but I think the powder contained citric acid and sodium hydrogen carbonate. In the mouth, water dissolves the powder and allows the components to react to form carbon dioxide gas to make a tingling sensation, water, and sodium citrate solution.

This was done to show an acid and base and gas-producing reaction.

***Slow antacid – Slowly, added vinegar (acetic acid) to milk of magnesia (magnesium hydroxide suspension) and universal indicator in water. The purple or blue color of the indicator in the basic suspension changed through the colors of the rainbow to pink or red as the acidic vinegar was added. However, if only a small amount of vinegar was added at a time, additional solid magnesium hydroxide dissociated to make the solution basic again. If enough acid was added, either vinegar or some other acid, the magnesium hydroxide was completely consumed and the mixture stayed red.

This was done to show acid and base and indicator color-changing reactions.

***Sulfur-laden coal samples – Showed coal samples with visible deposits of sulfur compounds. 

This was done to illustrate discussions about acid rain produced by sulfur oxides from sulfur in coal.

Combustion of magnesium – Burned a strip of magnesium metal in air, where oxygen in the air combined with the magnesium to produce solid magnesium oxide. *CAUTION: The burning metal is hot and produces an intense white light.

This was done to show a redox reaction.

Silver nitrate + copper metal – Placed a copper penny or strip of copper metal into a solution of silver(I) nitrate to illustrate a redox reaction. The silver(I) ions were reduced to form fuzzy silver metal crystals and the copper metal was oxidized to produce blue copper(II) ions.

This was done to show a redox reaction.

***Silver on hand – When silver(I) nitrate solution came into contact with skin, the silver(I) cations were reduced with the assistance of light to produce dark brown stains of silver metal. CAUTION: These stains are hard to remove.

This was done to show a redox reaction.

MudWatt battery – Purchased as a kit, bacteria in mud catalyzed the redox reaction between oxygen in the air and organic matter in mud. Electrons from this reaction were used to make an LED blink.

This was done to show a redox reaction.

Vitamin C reduces iodine in starch complex – Starch was added to brown iodine solution to produce a dark purple-black starch-iodine complex. Then, Vitamin C (ascorbic acid) was added to reduce the iodine complex to colorless iodide ions. This has been done in the palm of a hand, but can also be done in glassware.

This was done to show a redox reaction.

 

Ch6 - Gases

***Liquid nitrogen into soapy water – Liquid nitrogen was poured into a metal bucket containing warm water with a little dish soap added to produce a large volume of soapy foam.

This was done to show that the molar volume of a gas is much larger than the molar volume of the corresponding liquid.

***22.4 L volume vs ping-pong ball – Showed cardboard volume for a mole of gas at 0°C and 25 °C and volume of a ping-pong ball for roughly a mole of liquid.

This was done to show that the molar volume of a gas is much larger than the molar volume of the corresponding liquid.

***Plastic bottles filled at high-altitude – Showed plastic water bottles filled with air at the summit of Pike’s Peak and in the cabin of an airplane cruising at about ~35,000 feet, then sealed, and then brought back to Peoria, IL, altitude.

This was done to show how the volume of a sample of gas changes with different pressures at different altitudes.

***LEGO brick atmosphere sticks – Showed stacks of LEGO bricks with color schemes representing the gases in the atmospheres of Venus, Earth, and Mars.

This was done to illustrate discussions of mole percent and show differences in some planetary atmospheres.

***Helium vs. air balloon shrink – Showed balloons that had been filled to equal volumes with air and helium initially, and then after a few days the helium balloon was smaller than the air balloon.

This was done to show that lighter gases effuse through the balloon walls faster than heavier gases.

Alka-Seltzer poppers – Placed a half-tablet of Alka-Seltzer (containing citric acid and sodium hydrogen carbonate) into a Fuji-style film canister filled halfway with water and closed the canister. The water dissolved the tablet and allowed the components to react to form carbon dioxide gas, water, and sodium citrate solution. After 10-30 seconds the carbon dioxide pressure built up and popped the canister apart.

This was done to show that as the moles of a gas increases so does its pressure and to show an acid and base and gas-producing reaction.

Nitrous oxide (Whip-It) canister – Showed an empty canister found in a parking lot.

This was done to show an example of a small (formerly) pressurized gas container and to inform the class about the illegal practice of inhaling this gas.

Gas in plastic bottle in liquid nitrogen - Showed plastic water bottle filled with air before and after placing in liquid nitrogen to shrink the bottle.

This was done to show an example of gas volume decreasing as temperature decreasing (Charles’s Law).

Genie in bottle hydrogen peroxide decomposition – Added manganese(IV) oxide to 30% hydrogen peroxide in a narrow-mouth container to catalytically decompose the peroxide to produce an oxygen gas and water plume. CAUTION: Hydrogen peroxide is a powerful oxidizer and the demonstration produces manganese(IV) oxide particles in the air that could be inhaled. We placed have a moratorium on this demonstration.

This was done to show as the moles of a gas increases so does its volume (Avogadro’s Law) and to show a redox reaction.

Levitating bubbles – Blew bubbles onto a carbon dioxide layer produced by dry ice, where they floated on the dense gas.

This was done to show that gases that have a higher molar mass than the average molar mass of air can settle below air.

Scented candle – Placed a scented candle in the classroom for students to smell.

This was done to show an example of diffusion of gases.

 

Ch7 - Thermochemistry

***Flame of grill lighter or propane torch – Burned butane or propane, combustion reactions that can be easily controlled and do not produce smoke.

This was done to show the difference between a thermochemical system and its surroundings and an example of an exothermic reaction.

***Alka-Seltzer with water and thermometer – Placed a tablet of Alka-Seltzer (containing citric acid and sodium hydrogen carbonate) into water with a thermometer. As the water dissolved the tablet, the components reacted to form carbon dioxide gas, water, and sodium citrate solution, the temperature of the solution dropped. This might be due to the endothermic heat of solution of sodium hydrogen carbonate.

This was done to show an example of an endothermic process.

***Whack-a-Pack balloon – Struck a self-inflating balloon containing water, citric acid, and sodium hydrogen carbonate. The components reacted to form carbon dioxide gas, water, and sodium citrate solution. The carbon dioxide inflated the balloon. The temperature of the liquid in the balloon dropped. This might be due to the endothermic heat of solution of sodium hydrogen carbonate.

This was done to show as the moles of a gas increases so does its volume (Avogadro’s Law) and to show an acid and base and gas-producing reaction and to show an endothermic process.

***Hydrogen peroxide decomposition catalyzed by iron oxide - Added iron oxide to 3% hydrogen peroxide with dish soap and sulfuric acid added to catalytically decompose the peroxide to produce oxygen gas (and water) foam and heat.

This was done to show as the moles of a gas increases so does its volume (Avogadro’s Law) and to show an exothermic redox reaction.

***Iron heat pack in plastic bottle – Poured the contents of an iron powder based heat pack into an empty plastic water bottle. As the iron powder draws the oxygen from the air in the bottle to form iron oxide in an exothermic reaction, the bottle collapses.

This was done to show as the moles of a gas decreases so does its volume (Avogadro’s Law) and to show an exothermic redox reaction.

International food energy – Showed wrappers showing energy values of food from other countries.

This was done to show varying energy units for food.

Ethanol cannon popper – Used an Oudin coil to make a spark between nails to ignite ethanol vapors in air in a bottle to produce carbon dioxide and water vapor to pop a cork out of the bottle.

This was done to show an exothermic reaction that resembles combustion of fuel in a car cylinder.

Lycopodium powder in flame – Added lycopodium powder to a flame to produce a small fireball.

This was done to show that higher surface area can produce faster reactions and to show an exothermic reaction.

 

Ch8 - Quantum-Mechanical Model of the Atom

***The quantum ladder - Stood on various rungs of a ladder to represent an electron at various energy levels in an atom. Moved up various rungs when caught colored balls representing photons thrown by students. Moved down various rungs when threw colored balls away.

This was done to show the movement of electrons between energy levels in an atom as light is absorbed.

***Gas discharge tubes – Used an Oudin coil to excite the gases in discharge tubes. Sometimes used diffraction gratings for students to examine the colors produced.

This was done to show light emission from electrons energy moving between levels in atoms.

***UV beads – Showed UV light absorbing beads.

This was done to show molecules absorbing UV light.

Crookes tube – Showed how magnets can deflect a beam of electrons in a Crookes tube.

This was done to show that electron beams can be deflected by electromagnetic fields. Connection can be made to cathode ray tubes like in old TV and computer screens.

Alcohol flame colors – Showed colors from burning alcohol containing various cations.

This was done to show light emission from electrons energy moving between levels in atoms.

Electric pickle – Showed yellow light emission from excited sodium ions in pickle subjected to alternating electric current.

This was done to show light emission from electrons energy moving between levels in atoms.

 

Ch9 - Periodic Properties of the Elements

***Clock reaction – Showed the class an iodine-based clock reaction.

This was done to show a complex iodine based reaction.

***Glow screen, lasers, and radium girl statue – Shined red, green, and violet lasers on glow in the dark screen (only violet glows). Told the story of the painters who died of radium contamination and showed a picture of the “radium girl” memorial in Ottawa, IL.

This was done to show how radium has similar chemistry to calcium (Group 2 of the periodic table), and by describing diode compositions make a comparison to laser color (Group 15 of the periodic table).

***Cell phone screen – Showed a cell phone and noted that Gorilla Glass used in many cell phone screens is hardened by replacing sodium ions with potassium ions.

This was done to show an effect of replacing similar ions with different sizes (Group 1 of the periodic table).

Glassy metal bounce – Bounced metal ball bearings off crystalline stainless steel and amorphous glassy metal alloys. The bearings bounced higher from the harder amorphous alloy surfaces.

This was done to show effect of adding tiny beryllium atoms to help make the alloy amorphous.

Table salt, galena – Showed rocksalt structures of NaCl and PbS.

This was done to show that ion sizes and arrangements influence the crystal pattern and cleavage pattern of crystalline solids.

Colorful transition metals vs colorless main group metals – Showed samples of compounds of transition and main group metals.

This was done to illustrate that the electronic structure of metal ions influences their colors.

 

Ch10 - Chemical Bonding I

***Hand sanitizer spray on thermal paper – Sprayed ethanol on thermal paper to promote an acid-base reaction to darken the paper.

This was done to show a reaction with bonds breaking and forming in complex molecules and to show an acid and base and color changing reaction.

 


Video 3: Blue bottle experiment using sports drink and a base, Chem Demos YouTube Channel, September 11, 2020, (Watch more videos of demos highlighted here on the .2)

 

***Blue bottle reaction – Added potassium hydroxide to blue Gatorade to initiate oxidation of sugar by oxygen in the air. Color of Erioglaucine dye changed from blue to colorless as it was reduced by sugar and then back to blue as it was reoxidized by oxygen. (See video 3)

This was done to show a reaction with bonds breaking and forming in complex molecules and to show a redox reaction.

Balloons illustrate VSEPR – Used balloons to represent electron groups in VSEPR molecular model.

This was done to provide three-dimensional models for molecular geometry.

***Molecular geometry models - Used molecular models to represent bonding structures.

This was done to provide three-dimensional models for molecular geometry.

 

Ch11 - Chemical Bonding II

***Magnetic attraction – Showed that bringing together attracting magnets releases energy, but pulling apart attracting magnets needs energy input.

This was done to illustrate bond enthalpy.

***Fuel cell car with hydrogen, oxygen, and water bond models – Showed a hydrogen-oxygen fuel cell providing electricity to move a motor and wheels. Used ball-and-stick models to show bonds breaking and forming in the reversible reaction of water to form hydrogen and oxygen.

This was done to illustrate bond enthalpy.

Palladium in PDMS hydrogenation catalysts – Showed palladium metal nanoparticles suspended in polydimethylsiloxane used as a hydrogenation catalyst.

This was done to illustrate a bond enthalpy calculation.

***Orbital and bonding models – Showed models of unhybridized, hybridized, and molecular orbitals.

This was done to provide three-dimensional models for orbital structures.

***Polarizers and LCD displays – Showed polarizers and an LCD cell phone display.

This was done to show how electric fields can reorient molecular dipoles.

***Red, green, and blue LEDs - Showed red, green, and blue LEDs and how their colors can mix to produce a variety of colors.

This was done to show how by describing diode compositions make a comparison to color (Group 15 of the periodic table and electronegativity differences between atoms).

***PVDF “flicker strip” – Flexed polyvinylidene difluoride film between metal films to produce electricity to light a neon bulb.

This was done to show how changing the orientation of dipoles in piezoelectric materials can produce voltage differences.

Flash rocks – Struck together polycrystalline quartz rocks to produce electric discharges to light up the rocks.

This was done to show how changing the orientation of dipoles in piezoelectric materials can produce voltage differences.

***Pencils illustrate vectors – Showed how to use pencils to represent bond and overall dipole vectors in three dimensions.

This was done to provide a way to visualize the addition of dipole vectors in three dimensions.

Protein model kit – Showed an example of a protein model (including ribbon representation).

This was done to show a glimpse of a biochemical representation of biomolecules.

 

Ch12 Liquids, Solids, and Intermolecular Forces

***Hand boiler – Showed liquid in two sealed glass bulbs at low pressure connected by a tube. When the heat of a hand was applied to one bulb, the vapor pressure in that bulb increased and pushed the liquid through the tube to the other bulb, where it fountained up and looked like it was boiling.

This was done to show the influence of heat on vapor pressure.

***Ice models – Showed models of the Ih and Ic phases of ice.

This was done to show hydrogen bonding in ice, why snowflakes have hexagonal symmetry, and that solid species can have more than one solid phase.

***Snowflake Bentley books – Showed the book Snowflake Bentley, about Wilson Bentley, and the book Snow Crystals, which contained his photomicrographs of snowflakes.

This was done to show the hexagonal symmetry of snowflakes and to describe an individual who was really dedicated to his craft.

***Sodium acetate hand warmers – Showed a hand warmer containing supersaturated sodium acetate solution. When the metal disk inside was flexed, crystals of solid sodium acetate formed and heat was produced.

This was done to show crystals and their nucleation, supersaturation, and an exothermic process.

Corn syrup viscosity – Showed a sample of corn syrup and its viscous flow.

This was done to show an example of a liquid that is more viscous than water.

Paradichlorobenzene sample – Showed crystals of paradichlorobenzene that had been sublimed from the bottom and then deposited on the walls of its storage container.

This was done to show an example of an organic compound with weak intermolecular forces.

Carbon models – Showed models of various carbon structures.

This was done to show models of the structures of various carbon phases.

Paper graphene snowflake – Showed a model of graphene made from folded and cut paper.

This was done to show a model of the structure of graphene and graphite.

Quartz crystal samples – Showed quartz samples. 

This was done to show an example of a network covalent compound.

Large candle volcano – Showed a large wax candle that had been melted from underneath, expanded, and “erupted” out the top of the candle.

This was done to show that many liquids, like wax and lava, are less dense than the corresponding solid.

 

Ch14 - Solutions

***Two-phase bottle – Showed a plastic bottle containing a layer of yellow corn oil over a layer of water with blue food coloring. When the bottle was shaken, the phases mixed. When the bottle became still, the phases separated again.

This was done to show polarity, solubility, and the idea of “like dissolves like”.

Two-phase bottle with soap – Showed a plastic bottle containing a layer of yellow corn oil over a layer of water with blue food coloring, all with a little bit of dish soap added. When the bottle was shaken, the phases mixed. When the bottle became still, the phases eventually separated again, but much more slowly than when soap was not added.

This was done to show polarity, solubility, and the amphiphilic nature of soap.

Soda bottle – Showed a closed soda bottle and noted soda had no bubble with high headspace carbon dioxide pressure. Opened the bottle and bubbles formed when the headspace pressure dropped and the carbon dioxide solubility of the soda decreased.

This was done to show Henry’s Law, where gas solubility decreased as its pressure decreased.

Sodium polyacrylate snow – Added water to sodium polyacrylate, which absorbed the water and made the polymer swell. Water evaporating from the polymer made it feel cool.

This was done to show water dissolving into an ionic compound with ion dipole attractions and to show evaporative cooling.

 

Other

Happy Meal box with Barbie doll chemist – Showed a McDonalds Happy Meal box with a Barbie doll promotion on the side. One of them had a lab coat and was dressed like a chemist.

This was done to show an interesting role model promotion.

Fridge magnets – Showed class how sliding flexible sheet refrigerator magnets across each other can reveal how the magnetic poles are arranged in the sheets.

This was done to show how macroscopic probes can be used measure atomic scale forces and atomic scale structures.

Space shuttle tile – Passed around a heat shield tile from the space shuttle program and described it as made of lightweight and heat resistant sintered glass fibers.

This was done to show an advanced material comprised of an amorphous network covalent material.

Tektite – Showed glass produced by meteor impact.

This was done to show an exotic material comprised of an amorphous network covalent material.

Baby carrots in regular vs salt water – Showed a baby carrot that had been soaked in tap water as being crisp and a baby carrot soaked in salt water as being soggy.

This was done to show the impact of osmotic pressure on cells.

 

Safety: I have worked to maximize safety, but each demonstration and prop comes with its own particular set of safety considerations. If physical classroom examples are to be done in-person, then instructors must identify and respond to potential hazards, personal protective equipment, and disposal issues associated with these examples.

 

Acknowledgements: This work was supported by Bradley University and the Mund-Lagowski Department of Chemistry and Biochemistry with additional support from the Illinois Heartland Section of the American Chemical Society and the Illinois Space Grant Consortium. Special thanks to Audrey Stoewer for developing the video website.

 

References

1.   Tro, N. J. Chemistry: A Molecular Approach, 5th Edition; Pearson Education, Inc., 2020.

2.   Bradley University Chemistry Club. Demo Videos. https://sites.google.com/mail.bradley.edu/bradleychemdemos/demo-videos (accessed January, 2022).

Collection: 

Safety

General Safety

For Laboratory Work: Please refer to the ACS .  

For Demonstrations: Please refer to the ACS Division of Chemical Education .

Other Safety resources

: Recognize hazards; Assess the risks of hazards; Minimize the risks of hazards; Prepare for emergencies