S120: Chemical Rxns – Synthesis & Decomposition – Zn & I2

Introduction

The reaction of zinc metal with iodine shows direct combination, decomposition, recrystallization of sublimed I2, and electrolysis.

Zn(s) + I2(s) → No Reaction               

Zn(s) + I2(s)   H2O→ ZnI2(aq)

Zn2+ + 2I- → Zn + I2  

Mixture of Zn + I2 before water is added.

Iodine vapor is produced when water is added. ZnI2 is formed.

Filter contents to isolate clear, colorless ZnI2.

ZnI2 is poured into petri dish to submerge copper wires from DC power source.

When power is connected, Zn and I2 crystals are formed.

Close up of Zn deposits.

To Conduct Demonstration

  1. Mix Zn and I2 in a dry beaker on the overhead projector (no reaction).
  2. Add 40mL of di water a bit of a time with ventilation (copious violet fumes of iodine).
  3. Stir the mixture well and filter.  Pour filtrate into the petri dish (clear, colorless solution).
  4. Connect copper wires to the DC source.  Place the wires in the petri dish so that they are well-separated and immersed in solution.  Turn on the power supply.  (Amber coloration at anode, zinc accumulation on cathode).

Demo Time: ~4 minutes

Safety 

Perform in a well-ventilated room to avoid breathing iodine vapors.

Reference

Tested Demonstration, J.Chem.Ed., 1965

Acknowledgment

John Ohlsson, Spring 1987
Reformatted by Lora Ruffin and Michael Polk, Summer 2009