Reversible Tin Man
Publication No. 12771
What happens in an electrolytic cell if one of the ions in the electrolyte may be both oxidized and reduced? Electrolysis of tin(II) chloride provides a stunning example. Grow a beautiful “tin-man” crystal tree by running an electric current through a solution of tin(II) chloride. Students will enjoy watching this “electric” oxidation–reduction demonstration as tin crystals are produced and then redissolved when the direction of the current is reversed.
Electrolysis is the process of using an electric current to decompose compounds. An electrolytic cell requires several components including a power source, anode and cathode and an electrolytic conducting solution. Oxidation occurs at the anode and reduction occurs at the cathode. Typically in an electrolytic cell, the positive electrode is the anode and the negative electrode is the cathode. In this demonstration, an electrical current is passed through a solution of tin(II) chloride.
Copper wire, 1–2 cm (optional)
Tin(II) chloride solution, SnCl2 (stannous chloride), 1 M in HCl, 200 mL*
Battery cap with alligator clip leads*
Paper clips, small, 2
*Materials included in kit.
The acidic tin(II) chloride solution is a 1 M hydrochloric acid solution that is corrosive to body tissue and moderately toxic by ingestion. Avoid contact of all chemicals with eyes and skin. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Please consult current Safety Data Sheets for additional safety, handling and disposal information.
Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulations that may apply, before proceeding. Leftover tin(II) chloride solution may be neutralized and treated according to Flinn Suggested Disposal Method #24b. All solid waste may be disposed of in the trash according to Flinn Suggested Disposal Method #26a.
Student Worksheet PDF
Correlation to Next Generation Science Standards (NGSS)†
Science & Engineering PracticesAsking questions and defining problems
Developing and using models
Planning and carrying out investigations
Analyzing and interpreting data
Using mathematics and computational thinking
Constructing explanations and designing solutions
Disciplinary Core IdeasMS-PS1.A: Structure and Properties of Matter
MS-PS1.B: Chemical Reactions
MS-PS3.B: Conservation of Energy and Energy Transfer
HS-PS1.A: Structure and Properties of Matter
HS-PS1.B: Chemical Reactions
HS-PS3.B: Conservation of Energy and Energy Transfer
Cause and effect
Systems and system models
Energy and matter
Stability and change
MS-PS1-2. Analyze and interpret data on the properties of substances before and after the substances interact to determine if a chemical reaction has occurred.
Answers to Questions
The original conducting solution was tin(II) chloride (SnCl2). The products of the electrolysis reaction are tin(0) and tin(IV) chloride.
First Demonstration Second Demonstration
Accept any reasonable student sketches.
One of the products, tin(0), has a metallic, crystalline appearance, growing in feather-like projections outward from the negative electrode (cathode) and expanding across the Petri dish. The other product, tin(IV) chloride, is a milky white precipitate that remained localized near the electrode (anode).
a. Which product results from reduction of tin(IV) ions?
b. Which product results from oxidation of tin(IV) ions?
The products seemed to “reverse” their position. The original tin crystals and tin(IV) precipitate slowly redissolved and disappeared. Once the products from the first demonstration completely dissolved back into solution, new products formed at both electrodes. Since the placement of the anode and cathode was switched, the location of each product was also reversed.
This demonstration utilizes an electric current to cause an oxidization–reduction reaction within a solution of tin(II) chloride. Tin(II) ions are oxidized to an insoluble precipitate of tin(IV) chloride ions at the anode and reduced to metallic tin [tin(0)] at the cathode.
Sn4+(aq) + 4Cl (aq) → SnCl4(s)
Reduction half-reaction (cathode) Sn2+(aq) + 2e– → Sn(s)
This activity was adapted from Electrochemistry, Flinn ChemTopic™ Labs, Volume 17, Cesa, I., Ed.; Flinn Scientific: Batavia, IL, 2003.