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Electrochemical cells and chemical energy
Chemical reaction beteween a copper sulphate solution and zinc
The purpose is to study the
chemical transformation between metallic zinc and a solution of copper
Realization: zinc powder is placed in a test tube. The tube is stirred
and then the result is observed.
- Touching the test tube we can feel that it is abnormally hot. A
temperature measurement with a thermometer can be used to confirm that
the temperature of the solution is significantly higher after mixing
solution of copper sulphate that is initially blue becomes almost
- Zinc powder changes color: it takes an orange color which recalls
that of copper
A test is performed to identify ions in solution.
Sodium hydroxide is added and a precipitate is obtained which is not
blue but white.
This test suggests that copper ions have disappeared from the aqueous
solution and have been replaced with zinc ions which form a white
precipitate with sodium hydroxide
disappearance of the blue color and the absence of blue precipitate
during the test indicates that the copper ions have been consumed.
These ions have formed metallic copper on the remaining zinc powder.
The test also indicates that zinc ions have formed from zinc atoms.
ions don't undergo any particular modification and remain in solution
after the chemical transformation where they form, with zinc ions, a
solution of zinc sulfate.
These transformations can be summarized by the following chemical
+ copper sulphate
+ zinc sulphate
This chemical transformation is also accompanied by heat release.
The chemical energy present in the reactants is partly released as heat
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