Reaction of Zinc and Iodine

1. Reaction of Zinc and Iodine Zinc and iodine react by a combination reaction with the liberation of a purple cloud of iodine vapor

2. Purpose • To observe a combination reaction • To understand that a combination reaction is a redox reaction

3. Demonstration • The test tube in this reaction became too hot to touch, causing iodine to sublime into the inverted florence flask • Water was added to initiate the reaction • The purple vapor was sublimated iodine which was in excess beyond the amount needed to react with the zinc

4. Concepts 1. Combination Reactions 2. Redox Reactions 3. Ionic Compounds

5. 1. Combination Reactions • In a combination reaction two individual substances combine to a single compound • In this demonstration Zn + I2 ZnI2

6. 2. Redox Reactions • In a redox reaction, one substance loses electrons while another substance gains electrons • “Redox” is a conventional term which is a combination of the words “reduction” AND “oxidation” • In this demonstration zinc is oxidized and iodine is reduced Zn + I2 ZnI2 Loses its electrons Gains electrons from Zn

7. 3. Ionic Compounds • Zinc is on the left side of the Periodic Table hence is a metal and will lose electrons to form a positive ion Zn2+ • Iodine is on the right side of the Periodic Table hence is a non-metal and will gain the electrons lost by zinc to form I1- • In the final compound two iodide 1- ions are required for each zinc 2+ ion to form ZnI2

8. Conclusions • Zinc was oxidized to Zn2+ and iodine was oxidized to I_ • The product of this combination was a single new compound, zinc iodide • The reaction was exothermic and caused the excess iodine to sublime into purple vapor

9. Comments • Upon cooling the flask the iodine vapors condense to the solid iodine on the sides of the flask • This is both a combination reaction and a redox reaction