Replacement reactions

1. Evidences of rx
• Changes:
– Color
– Temperature
– PS: production of gas, ppt
– pH
– smell
• Fire

2. Replacement reaction
• A + BC AC + B (A and B are metals)
• “Single replacement”
• What to look for Element + compound on each
side of equation

3. Reaction # 1
Replacement
• Zn(s) + HCl(aq)
• 6M HCl in test tube (~ ½ full, measure)
• ~ 1 t Zn in balloon (tare balloon, weigh)
• Complete and balance equation, what is in the balloon at
the end of the reaction? PS? – relate to stoichiometry
• What evidences that a reaction occurred?
• What is LR, ER??

4. Zn(s) + 2HCl(aq) ZnCl2(aq) + H2(g)

5. Replacement Reaction # 2
• Zn(s) + CuSO4(s)
• ¼ test tube copper sulfate (or copper chloride)
• Add Zinc
• Note changes, balance equation

6. Replacement Reaction # 2
• Zn(s) + CuSO4(s) Cu(s) + ZnSO4(aq)
• If there is a limited amount of copper sulfate,
the solution will become colorless as all the
copper ions are converted to copper metal
• The Zinc ions produced are colorless

7. • Zinc is considered more active than copper
• Zinc “replaces” copper in the compound
– Later when we look at redox reactions
– Electrons move from Zinc (making it a soluble Zinc
ion) to copper (making it an insoluble metal)
– The sulfate ions are called “spectator ions” – they
do not play a part in the reaction

8. Reaction # 3
Replacement
• Fe(s) + CuSO4(aq)
• Steel wool in test tube, add copper
sulfate to ½ the level of the steel wool
– observe
• Make observations, complete balanced
equation

9. Fe(s) + CuSO4(aq) FeSO4(aq) + Cu(s)
Steel wool on the left,, “copper wool” on the right
Note original blue color of copper sulfate solution
In left hand solution
On the right all the copper ions have “plated out”
as copper metal, the blue color of the solution is
gone!

10. Reaction #4
Replacement Reaction
• Cu(s) + ZnSO4(aq)
• ¼ test tube or beaker of ZnSO4 add copper
turnings
• Observe

11. • Copper does not push Zinc out of a compound
spontaneously
– You can “push” this reaction in the reverse by
“pushing “ an electrical current through it!!

12. Do all possible replacement reactions
occur?
• Activity series “what can replace what”
• Metals and H:
…….

13. Activity Series for Metals
Can be used to predict the outcome of replacement reactions
• Listed Most Active to Least Active
• Li K Ba Ca Na Mg--- Al Mn Zn Cr Fe Co Ni Sn PbHCu Ag Hg Pt Au
• Any element on the list can replace from a compound
elements to its right
• Everything to the left of H can push H out of an acid
• Everything to the left of the “---” can push H out of water
• Elements to the right of H do not react with acids by
replacing H (copper has a redox reaction with
concentrated nitric acid, but does not react with other
acids)