Write the (net ionic) half-reactions of each experiment by identifying the two p
ID: 1020621 • Letter: W
Question
Write the (net ionic) half-reactions of each experiment by identifying the two products.
Label each half-reaction as an oxidation or a reduction.
Combine the two half-reactions of each experiment to give the net ionic equations.
Reactions:
1. Reaction of Cu2+ with Fe
Add ~2 mL (40 drops) of 0.5 M CuSO4 solution to a test tube. Add a small piece of steel wool (Fe) to the solution and mix until colorless. Decant the colorless solution into a clean test tube to be used in Reaction 3.
2. Reaction of Cu2+ with Zn
Add ~2 mL (40 drops) of 0.5 M CuSO4 solution to a test tube. Add a small piece of zinc metal to the solution and mix. After a fair amount of reddish-brown solid has formed and flaked off the piece of zinc metal, pour all of the solution and solids into a small beaker; rinsing if necessary. Remove the zinc piece with tweezers and set it aside for use in Reaction 6. Transfer the reddish-brown solid into a clean crucible and remove as much water as possible by decanting. Use the crucible and solid in reaction 5.
3. Reaction of Fe2+ with H2O2
Add 4 drops of 3% hydrogen peroxide to the colorless solution from 1. To help characterize the product, acidify the solution with 5 drops of 6 M HNO3, then add 1 drop of 0.1 M KSCN. Consult a table of standard reduction potentials for potential half-reactions of H2O2.
4. Reaction of Mg with O2
Grasp a piece of Mg ribbon with crucible tongs and hold the Mg in the flame until it ignites. Do not look directly at the reaction until it is over. Look at the tips of the tongs when the reaction is over.
5. Reaction of Cu with O2
Place the crucible from Reaction 2 on a clay triangle supported by a ring and ring stand. Adjust the ring height to allow the hottest part of the Bunsen burner flame to just touch the bottom of the crucible. Gently heat the contents of the crucible until dry, then strongly for five minutes. Do reactions 6, 7, and 8 while it is heating. Carefully stir the contents of the crucible with a stirring rod and heat again for two minutes. Allow to cool. To help characterize the product, transfer the solid from the crucible to a test tube, add ten drops of 10% HCl and mix until dissolved. Add 10 drops of concentrated ammonia.
6. Reaction of Zn with H+
Place the zinc saved from Reaction 3 in a test tube and add ~2 mL of 10% HCl. Observe the reaction, dilute with distilled water to slow the reaction, and discard.
7. Reaction of Mg with H+
Place a piece of Mg ribbon in a test tube. Add about 2 mL of 10% HCl.
8. Reaction of Cl2 with I–
Place ~1 mL of 0.1 M KI solution in a test tube. Add several drops of aqueous Cl2 to the test tube just until a color change is observed. In order to characterize the product of the reaction above, add 1-2 drops of 1 M Na2S2O3 solution. Note what happens initially.
Explanation / Answer
(1) Oxidation half reaction : Fe (s) -----> Fe2+ (aq.) + 2 e
Reduction half reaction : Cu2+ (aq.) + 2 e ---------> Cu(s)
Net ionic equation : Cu2+ (aq.) + Fe (s) ------> Cu (s) + Fe2+ (aq.)
(2) Oxidation half reaction : Zn (s) -----> Zn2+ (aq.) + 2 e
Reduction half reaction : Cu2+ (aq.) + 2 e ---------> Cu(s)
Net ionic equation : Zn (s) + Cu2+ (aq) ------> Cu (s) + Zn2+ (aq.)
(3) Oxidation half reaction : 2Fe2+ (aq.) ----------> 2Fe3+ (aq.) + 2 e
reduction half reaction: H2O2 (l) + 2H+ + 2e (aq.) -----------> 2H2O(l)
(4) Oxidation half reaction : 2 Mg (s) ----> 2 Mg2+ (aq.) + 4 e
reduction half reaction : O2 + 4 e ----------> 2 O2-
Net ionic equation : 2 Mg + O2 ----------> 2 Mg2+ + 2 O2-
(5) Oxidation half reaction: 2 Cu ----------> 2 Cu2+ + 4 e
Reduction half reaction : O2 + 4 e ----------> 2 O2-
Net ionic equation : 2 Cu + O2 ----------> 2 Cu2+ + 2 O2-
(6) Oxidation half reaction : Zn(s) ------> Zn2+ (aq.) + 2 e
reduction half reaction : 2 H + + 2 e ----------> H2
Net ionic equation: Zn + 2 H+ ---------> Zn2+ + H2
(7) Oxidation half reaction : Mg(s) ------> Mg2+ (aq.) + 2 e
reduction half reaction : 2 H + + 2 e ----------> H2
Net ionic equation: Mg + 2 H+ ---------> Mg2+ + H2
(8) Oxidation half reaction: 2 I- ------------> I2 + 2 e
reduction half reaction : Cl2 + 2 e ----------> 2 Cl-
Net ionic equation : 2 I - + Cl2 ----------> I2 + 2 Cl-
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