Gases Demonstrations

See also: Pressure and Fluids

Gas demonstrations involve collecting, observing, or producing gases through chemical reactions. They help make the invisible visible, allowing students to directly experience the behavior of gases.

Demonstration	Materials	Difficulty	Safety	Summary
Acetylene From Calcium Carbide	★★★	★★★	★★★	Acetylene gas is generated by reacting calcium carbide with hydrochloric acid.
Air Cannon Smoke Rings	★★☆	★★☆	★★☆	A large trash can fitted with a flexible plastic membrane can be used to create giant smoke rings. Striking the membrane sends a vortex of air through a hole, which can be made visible with smoke to demonstrate air movement and Bernoulli’s principle.
Ammonia and Hydrogen Chloride Diffusion	★★☆	★★☆	★★★	Cotton wool soaked with aqueous ammonia is placed at one end of a glass tube and cotton wool soaked with concentrated hydrochloric acid at the other. As the vapors diffuse toward each other, they form a visible white ring of ammonium chloride closer to the HCl end, showing that ammonia diffuses faster due to its lower molar mass.
Ammonia Fountain	★★★	★★★	★★★	Dry ammonia gas is collected in a sealed flask. When a small amount of water is injected, the ammonia rapidly dissolves, creating a partial vacuum that pulls water up into the flask. An indicator shows the resulting alkaline solution.
Blowing Up a Balloon with Baking Soda and Vinegar	★☆☆	★☆☆	★☆☆	When baking soda inside a balloon is released into vinegar in a bottle, an acid-base reaction produces carbon dioxide gas. The gas expands and inflates the balloon without using air from your lungs.
Balloon in Syringe Boyle's Law	★★☆	★☆☆	★☆☆	Using balloons inside a syringe, this experiment shows how gases expand when pressure decreases and contract when pressure increases, illustrating Boyle’s law.
Balloon Volume and Temperature	★☆☆	★☆☆	★☆☆	This experiment demonstrates how temperature affects the volume of gas inside a balloon. By placing balloons over bottles in hot water, a refrigerator, and a freezer, students observe how gases expand when heated and contract when cooled, illustrating Charles’s Law.
Molecular Mass of Butane	★★☆	★★☆	★★☆	Butane from a lighter is collected in an inverted water-filled graduated cylinder. The mass of the lighter before and after gas release is used to find the gas mass. Using the ideal gas law, the number of moles of butane is determined and its molar mass is calculated.
Carbon Dioxide Fire Extinguisher	★☆☆	★☆☆	★☆☆	Baking soda and vinegar react to produce carbon dioxide gas, which is then poured over lit candles to extinguish the flames. This models how fire extinguishers use gases to smother fire.
Carbonated Drink Shake Up	★☆☆	★☆☆	★☆☆	This demonstration explores what happens when a shaken soda can is opened. Shaking introduces bubbles that cling to the can’s inner surface. Opening the can releases pressure, causing these bubbles to expand and force liquid out in a foamy burst. By snapping the sides of the can before opening, bubbles are dislodged and float to the top, reducing the mess.
Electrolysis of Sodium Chloride (Brine)	★★☆	★★☆	★★☆	Aqueous sodium chloride is electrolyzed with inert electrodes to produce hydrogen gas at the cathode, chlorine gas at the anode, and sodium hydroxide remaining in solution.
Alka-Seltzer Rocket	★★☆	★☆☆	★☆☆	A plastic film canister filled with water and alka-seltzer creates carbon dioxide gas, building pressure until the lid pops off and launches the canister like a rocket.
Hydrogen Balloon Explosion	★★★	★★☆	★★★	A helium-filled balloon and a hydrogen-filled balloon are ignited to compare their reactions. The helium balloon produces no reaction, while the hydrogen balloon explodes with a loud sound and flame, illustrating combustion and the differences in gas properties.
Hydrogen Mini Rocket	★★☆	★★☆	★★★	Hydrogen and oxygen gases are produced in the lab through chemical reactions, then combined and ignited to propel a small rocket across the room. The demonstration highlights multiple types of chemical reactions: double replacement, decomposition, combustion, and synthesis.
Hydrogen and Oxygen Exploding Bubbles	★★☆	★★☆	★★★	Electrolysis of dilute sulfuric acid produces hydrogen and oxygen gases, which are collected as soap bubbles. When ignited, the bubbles explode with a loud “crack,” demonstrating electrolysis, gas recombination, and energy changes.
Limewater Test for Carbon Dioxide	★★☆	★☆☆	★☆☆	Carbon dioxide can be detected by bubbling the gas through limewater, which is a solution of calcium hydroxide. If carbon dioxide is present, the limewater turns milky or cloudy white due to the formation of calcium carbonate.
Making Chlorine Gas	★★☆	★★☆	★★★	Chlorine gas, a pale greenish-yellow substance, can be produced by reacting potassium permanganate with concentrated hydrochloric acid.
Making Nitrogen Dioxide	★★☆	★★☆	★★★	When copper metal is added to concentrated nitric acid, a vigorous reaction occurs that dissolves the copper, producing a blue-green solution of copper nitrate and releasing brown nitrogen dioxide gas.
Marshmallow in a Vacuum	★★★	★★☆	★★☆	Placing marshmallows inside a bell jar and changing the air pressure demonstrates how gases expand and contract, showing the effects of vacuum and differential pressure on porous materials.
Mentos and Diet Coke	★☆☆	★☆☆	★★☆	Dropping Mentos candies into Diet Coke causes a rapid release of dissolved carbon dioxide, creating a dramatic soda eruption. This is a physical reaction caused by surface roughness on the Mentos that accelerates bubble formation.
Nitrogen Dioxide and Dinitrogen Tetroxide Equilibrium	★★★	★★★	★★★	The equilibrium between brown nitrogen dioxide gas (NO2) and colorless dinitrogen tetroxide gas (N2O4) can be studied in a closed syringe system. Changes in pressure, volume, and temperature shift the equilibrium, which can be observed as changes in the intensity of the brown color.
Preparing and Testing Hydrogen Gas	★★☆	★☆☆	★★☆	Hydrogen gas is produced when zinc reacts with hydrochloric acid. The gas is collected over water and tested with a lit splint, which produces a distinctive ‘pop’ sound, confirming the presence of hydrogen.
Preparing and Testing Oxygen	★★☆	★☆☆	★★☆	Oxygen can be produced by decomposing hydrogen peroxide. The reaction is sped up by a manganese(IV) oxide catalyst. The gas can be tested with a glowing splint, which relights in oxygen.
Production of Ammonia Gas	★★☆	★★★	★★★	Ammonia gas is produced in the laboratory by heating a mixture of ammonium chloride and calcium hydroxide. The gas, being lighter than air and highly soluble in water, is collected by downward displacement of air.
Production of Ethylene	★★☆	★★★	★★★	Ethylene/Ethene gas (C2H4) is prepared by catalytic dehydration of ethanol using aluminum oxide. The gas can then be tested for unsaturation by its reaction with iodine water, showing the reactivity of alkenes.

Materials
★☆☆ Easy to get from supermarket or hardware store
★★☆ Available in most school laboratories or specialist stores
★★★ Requires materials not commonly found in school laboratories

Difficulty
★☆☆ Can be easily done by most teenagers
★★☆ Available in most school laboratories or specialist stores
★★★ Requires a more experienced teacher

Safety
★☆☆ Minimal safety procedures required
★★☆ Some safety precautions required to perform safely
★★★ Only to be attempted with adequate safety procedures and trained staff