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

3. Purpose n To observe a combination reaction n To understand that a combination reaction is a redox reaction

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

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

6. 1.Combination Reactions n In a combination reaction two individual substances combine to a single compound n In this demonstration Zn + I 2 ZnI 2

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

8. 3.Ionic Compounds n Zinc is on the left side of the Periodic Table hence is a metal and will lose electrons to form a positive ion Zn 2+ n 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 I 1- n In the final compound two iodide 1 - ions are required for each zinc 2+ ion to form ZnI 2

9. Conclusions n Zinc was oxidized to Zn 2+ and iodine was oxidized to I _ n The product of this combination was a single new compound, zinc iodide n The reaction was exothermic and caused the excess iodine to sublime into purple vapor

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