Growing Crystals in Gels
Publication No. 11974
Grow your own beautiful, long-lasting, demonstration-size crystals in gels!
In this experiment, you will grow crystals of two different substances—lead iodide and potassium hydrogen tartrate. 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. Display these gel crystals in a showcase to attract the attention of all.
Acetic acid solution, CH3COOH, 1 M, 540 mL*
Lead nitrate solution, Pb(NO3)2, 1 M, 35 mL*
Potassium chloride solution, KCl, saturated, 200 mL*
Potassium iodide, KI, 33 g*
Sodium silicate solution, (water glass), Na2Si3O7, 15%, 1 L*
Tartaric acid solution, H2C4H4O6, 3 M, 400 mL*
Bottles with caps, 1-L, 2*
Graduated cylinders, 100- and 500-mL
*Materials included in kit.
Lead solutions are toxic by inhalation and 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. Wash hands thoroughly with soap and water before leaving the laboratory.
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. Bottles that contain lead iodide crystals and excess lead nitrate should be disposed of using Flinn Suggested Disposal Method #27f. Potassium hydrogen tartrate crystals may be discarded in the solid waste disposal according to Flinn Suggested Disposal Method #26a.
Add 100 mL of deionized or distilled water to the potassium iodide bottle (AP8751C). 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.
Student Worksheet PDF
Correlation to Next Generation Science Standards (NGSS)†
Science & Engineering PracticesDeveloping and using models
Disciplinary Core IdeasMS-PS1.A: Structure and Properties of Matter
MS-PS1.B: Chemical Reactions
HS-PS1.B: Chemical Reactions
HS-PS1.A: Structure and Properties of Matter
Systems and system models
Stability and change
MS-PS1-4: Develop a model that predicts and describes changes in particle motion, temperature, and state of a pure substance when thermal energy is added or removed.
Answers to Questions
A gel hardened in the first bottle overnight. After potassium iodide was added, yellow, sheet-like crystals began to form at the interface between the gel and the solution. In the second bottle, the gel took three days to harden. When the potassium chloride solution was added, white, cubic crystals formed at the gel-solution interface. The crystals in both bottles grew downward, into the gel.
Pb2+(aq) + 2I–(aq) → PbI2(s) Lead Iodide CrystalsIn the second bottle, a double replacement precipitation reaction occurs with potassium tartrate forming as the solid.
K+(aq) + HC4H4O6–(aq) → KHC4H4O6(s) Potassium Hydrogen Tartrate Crystals
Special thanks to Tanya Phillips, Piedmont Unified School District, Piedmont, CA, for providing us with this activity. Tanya would like to thank Dr. Earle Scott, Professor Emeritus, Ripon College, WI, for introducing her to these wonderful crystals.