Electrodes made from pencil lead are attached to a 9V battery to electrolyze various solutions. Oxidation occurs and the anode and reduction occurs at the cathode. When a solution of tin (II) chloride is electrolyzed tin metal and chlorine gas are produced:
SnCl2 (aq) → Sn (s) + Cl2 (g)
When a solution of copper (II) chloride is electrolyzed copper metal and chlorine gas are produced:
CuCl2 aq) → Cu (s) + Cl2 (g)

Bubbling Magnesium

When magnesium ribbon is placed in hydrochloric acid, hydrogen gas is produced causing the mixture to bubble.
Mg (s) + 2HCl (aq) → MgCl2 (aq) + H2 (g)

If they hydrogen gas is collected, it can be ignited to demonstrate the potential safety concerns of an evolved gas.
H2 (g) + O2 (g) → H2O (g)

Mass the Gas

In this demo, baking soda and vinegar are mixed in a plastic storage bag. The reaction container is massed before and after the reaction for students to see the Law of Conservation of Mass in action.
NaHCO3 (s) + CH3COOH (aq) →CO2 (g) + H2O (l) + CH3COONa (aq)

Lemon Fizz

lemon reaction with baking soda

When basic baking soda (NaHCO3) is combined with acidic lemon juice (mainly citric acid, H3C6H5O7) an acid base reaction occurs. The reaction releases CO2 which can be captured using dish soap to form bubbles.
H3C6H5O7 (aq) + 3 NaHCO3 (s) → 3 CO2 (g) + 3 H2O (l) + Na3C6H5O7 (aq)

Genie in a Bottle

decomposition of hydrogen peroxide

This demo makes use of the catalytic decomposition of hydrogen peroxide to produce a column of steam out of a flask, that looks like a genie coming out of a bottle.
2H2O2 → 2H2O + O2, KI is a catalyst

Elephant’s Toothpaste

decomposition of hydrogen peroxide elephant's toothpaste old foamy

Hydrogen peroxide is decomposed quickly in liquid soap with the help of a catalyst to create a large volume of foam that grows out of a graduated cylinder. The soap bubbles contain oxygen.
2H2O2 → 2H2O + O2, KI is a catalyst

Chemistry Pop Guns

This demo harnesses the reaction of baking soda and vinegar to blow a cork off a test tube.
NaHCO3 (s) + CH3COOH (aq) →CO2 (g) + H2O (l) + CH3COONa (aq)

Aluminium Foil and NaOH

aluminum foil and sodium hydroxide produce hydrogen gas

This demo simulates what happens when Drano is poured down a clogged drain; the hydrogen gas produced forces gunk out of the drain. Also, this demonstration is a good safety example of why bases need to be handled carefully – they can be corrosive, especially to metals. If the hydrogen gas is collected and ignited, this demo shows the safety hazards that evolved gases can have.
2Al + 2NaOH + 6H2O → 2NaAl(OH)4 + 3H2