8.2 CHAPTER 8. TYPES OFREACTIONS
copper sulphate
solutionzinc granulesMethod: Add the zinc granules to the copper sulfatesolution and observe what happens.
What happens to the zinc granules? What happens to the colour of the solution?
Results:- Zinc becomes coveredin a layer that looks likecopper.
- The blue copper sulphate solution becomes clearer.
Cu2+ions from the CuSO 4 solution are reduced to form copper metal.This is what you saw
on the zinc crystals. Thereduction of the copperions (in other words, their removal from the
copper sulphate solution), also explains the change in colour of the solution (copper ions in
solution are blue). The equation for this reactionis:
Cu2++ 2e−→ Cu
Zinc is oxidised to form Zn2+ions which are clear inthe solution. The equation for this
reaction is:
Zn→ Zn2++ 2e−
The overall reaction is:
Cu2+(aq) + Zn(s)→ Cu(s) + Zn2+(aq)
Conclusion: A redox reaction has taken place. Cu2+ions are reduced and thezinc is oxidised.Below are some furtherexamples of redox reactions:
- H 2 + F 2 → 2HF can be re-written as twohalf-reactions:
H 2 → 2H++ 2e−(oxidation) and
F 2 + 2e−→ 2F−(reduction)- Cl 2 + 2KI→ 2KCl + I 2 or Cl 2 + 2I−→ 2Cl−+ I 2 , can be written as two half-reactions:
Cl 2 + 2e−→ 2Cl−(reduction) and
2I−→ I 2 + 2e−(oxidation)In Grade 12, you will go on to look at electrochemical reactions, andthe role that electron transfer
plays in this type of reaction.
See video: VPjql at http://www.everythingscience.co.za
Exercise 8 - 3
- Look at the followingreaction:
2 H 2 O 2 (�)→ 2 H 2 O(�) + O 2 (g)(a) What is the oxidation number of the oxygenatom in each of the following compounds?
i. H 2 O 2
ii. H 2 O