12 - 18 Years
Prep: 15 mins
Activity: 10 mins hands-on, 24 hr total
Youtube ID: SYKYbMYHbok
Customize Activity to Venue
Identify Safety Practices
Introduce the Tin Solution
Here are some key themes to explore with the audience once the activity is complete. Adjust the details to match the level of your audience.
The formation of tin crystals from the tin(II) chloride solution is an example of electrolysis. In electrolysis, an electric current induces a chemical reaction in which reactants are reduced (gains electrons) and oxidized (loses electrons), or a redox reaction.
In this activity, the SnCl2 completely dissociates in water to form Sn2+ and Cl- ions. These ions (plus the ions from the acid) create an electrolyte solution, or a solution capable of carrying a current. The battery powers a current that runs through the circuit created by the battery, connecting wires, paper clips, and electrolyte solution.
In the petri dish, the current drives a disproportionation reaction. Disproportionation is a type of redox reaction in which a single reactant iform both oxidized and reduced products.
Reduction takes place at the cathode, where half of the tin(II) chloride gains two electrons to become tin metal. This half of the reaction can be written as:
Sn2+(aq) + 2e- → Sn(s)
(Cl- ions are not shown here because they neither gain nor lose elections in this process.)
Oxidization takes place at the anode, where the half of the tin(II) chloride loses two electrons to become tin(IV) chloride. This half of the reaction can be written as:
Sn2+(aq) → Sn4+(aq) + 2e-
Tin(IV) chloride is insoluble and the white precipitate you see at the anode.
Sn4+ (aq) + 4Cl- → SnCl4(s)
The overall reaction is:
2Sn2+(aq) + 4Cl-(aq) → SnCl4(s) + Sn(s)
If you added a piece of wire to the petri dish, it forms an additional electrode, with the oxidation and reduction reactions repeating at either end.
Electrolysis is a common technique for purifying metals and coating surfaces. It is also used to split water (H2O) into hydrogen and oxygen gases for clean energy sources and is researched for other green applications.