Publication No. 10087
Growing Crystals in Gels
Student Laboratory Kit
Add 100 mL of deionized or distilled water to the bottle of solid potassium iodide. Cap and shake the bottle vigorously until all solid is in solution. Potassium iodide solution has a poor shelf life. Prepare this solution a few minutes prior to the lab.
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. Gel crystals may be stored indefinitely. Seal test tubes with Parafilm M®. Test tubes that contain lead crystals should be treated according to Flinn Suggested Disposal Method #27f. Liesegang rings and all other gel crystals may be discarded according to Flinn Suggested Disposal Method #26a.
Correlation to Next Generation Science Standards (NGSS)†
Science & Engineering PracticesAsking questions and defining problems
Planning and carrying out investigations
Analyzing and interpreting data
Engaging in argument from evidence
Obtaining, evaluation, and communicating information
Constructing explanations and designing solutions
Disciplinary Core IdeasMS-PS1.A: Structure and Properties of Matter
MS-PS1.B: Chemical Reactions
HS-PS1.A: Structure and Properties of Matter
HS-PS1.B: Chemical Reactions
Crosscutting ConceptsEnergy and matter
Systems and system models
Scale, proportion, and quantity
Cause and effect
MS-PS1-1. Develop models to describe the atomic composition of simple molecules and extended structures.
The reaction in test tube l can generally be called a single replacement reaction. It can be understood further if we also call it an oxidation-reduction reaction, where iron is being oxidized and copper is being reduced.
Fe(s) + Cu2+(aq) → Fe2+(aq) + Cu(s) Copper Crystals
In test tube 2, a single replacement oxidation–reduction reaction also occurs. Zinc is being oxidized and lead is being reduced.
Zn(s) + Pb2+(aq) → Zn2+(aq) + Pb(s) Lead Crystals
In test tube 3, a combination precipitation reaction occurs. The lead and iodide ions combine to form the lead iodide solid.
Pb2+(aq) + 2I–(aq) → PbI2(s) Lead Iodide Crystals
In test tube 4, a double replacement precipitation reaction occurs with potassium tartrate forming as the solid.
K+(aq) + HC4H4O6–(aq) → KHC4H4O6(s) Potassium Tartrate Crystals
In test tube 5, a double replacement precipitation reaction also occurs with copper(II) tartrate forming as the solid.
Cu2+(aq) + 2HC4H4O6–(aq) → Cu(HC4H4O6)2(s) Copper(II) Tartrate Crystals
In test tube 6, a double replacement precipitation reaction occurs with copper(II) chromate forming as the brown Liesegang rings.
Cu2+(aq) + CrO42–(aq) → CuCrO4(s) Copper(II) Chromate Precipitate
Special thanks to Tanya Phillips, Piedmont Unified School District, Piedmont, California for providing us with this activity. Tanya would like to thank Dr. Earle Scott, Professor Emeritus, Ripon College, Wisconsin for introducing her to these wonderful crystals.
Growing Crystals in Gels
Grow your own beautiful, long-lasting crystals in gels! Mix a dilute solution of sodium silicate (water glass) with an organic acid (usually acetic acid) in which an ion has been incorporated. A gel forms overnight. Then place another ionic solution or a metal on top of the hardened gel, and spectacular crystals of a new substance form in the gel as the aqueous ion slowly diffuses downward. The longer you permit these to grow, the more beautiful they become. In this experiment, you will grow crystals of six different substances—copper metal, lead metal, lead iodide, potassium hydrogen tartrate, copper(II) tartrate, and a copper(II) chromate Liesegang ring system. Although results can be seen within hours, the crystals become more enchanting after growing for 2–3 weeks. The crystals make a stunning year-long classroom display, and if not allowed to dry out, will last for decades. Students can grow them easily and are quickly motivated. Display these gel crystals in a showcase to attract the attention of all.
(for each group)
Acetic acid solution, CH3COOH, 1 M*
Copper(II) chloride solution, CuCl2, 1 M*
Copper(II) sulfate solution, CuSO4, 1 M*
Copper(II) sulfate solution, CuSO4, saturated*
Lead nitrate solution, Pb(NO3)2, 1 M*
Potassium chloride solution, KCl, saturated*
Potassium chromate solution, K2CrO4, 1 M*
Potassium iodide solution, KI, 2 M*
Sodium chloride solution, NaCl, 1 M*
Sodium silicate solution, Na2Si3O7, 15%*
Tartaric acid solution, H2C4H4O6, 3 M*
Zinc, 5" x ½" strip*
Water, distilled or deionized
Graduated cylinder, 25-mL
Paper clip, metal (steel)
Parafilm M® (optional)
Pipets or eyedroppers
Rubber stoppers, #2, 6*
Test tubes, 20 x 150 mm, 6*
Test tube rack
*Materials included in kit.
Lead solutions are toxic by inhalation and ingestion. Potassium chromate solution may be corrosive to body tissue. Chromium compounds are alleged carcinogens. Copper(II) sulfate solutions are toxic by ingestion. Avoid contact with eyes, skin and clothing. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Please review current Safety Data Sheets for additional safety, handling and disposal information.
Note: Tubes 1, 2, 3 and 6 will be hardened; tubes 4 and 5 may need three to four days.