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Chem 112 OXIDATION-REDUCTION EXPERIMENT
INTRODUCTION
An oxidation-reduction (redox) reaction involves the movement of electrons from one reactant to another. Many reactions that you have already studied are redox reactions; these include single replacement, combustion, and combination. Oxidation is the loss of electrons. Reduction is the gain of electrons. The loss and gain of electrons occur simultaneously in the reaction. For example, in the reaction of elemental calcium and oxygen to produce calcium oxide:
Ca(s) + ½ O 2 (g) → CaO(s)
Calcium loses two electrons and oxygen gains two electrons. Although the two events occur simultaneously, they may be written as two separate half-reactions:
Reduction half-reaction: 2 e-^ + ½ O 2 → O2-
Oxidation half-reaction: Ca → Ca2+^ + 2 e-
In this reaction, O 2 is the oxidizing agent. The oxidizing agent is the species that is being reduced (gaining electrons). The reducing agent is the species that is being oxidized (losing electrons). The reducing reagent in this reaction is Ca.
An oxidation-reduction reaction may be thought of as a competition between two substances for electrons. Consider the two reactions below, which are the reverse of each other:
Reaction (1) Cu(NO 3 ) 2 (aq) + Zn(s) → Cu(s) + Zn(NO 3 ) 2 (aq)
net ionic equation: Cu2+(aq) + Zn(s) → Cu(s) + Zn2+^ (aq)
reduction half-reaction: Cu2+^ (aq) + 2 e-^ → Cu(s)
oxidation half-reaction: Zn(s) → Zn2+^ (aq) + 2 e-
oxidizing agent = Cu2+ reducing agent = Zn
Reaction (2) Zn(NO 3 ) 2 (aq) + Cu(s) → Zn(s) + Cu(NO 3 ) 2 (aq)
net ionic equation: Zn2+(aq) + Cu(s) → Zn(s) + Cu2+(aq)
reduction half-reaction: Zn2+^ (aq) + 2 e-^ → Zn(s)
oxidation half-reaction: Cu(s) → Cu2+(aq) + 2 e-
oxidizing agent = Zn2+ reducing agent = Cu
Reaction (1) will occur spontaneously and (2) will not if Cu2+^ is a stronger oxidizing agent than Zn2+. Conversely, reaction (2) will occur and (1) will not if Zn2+^ is a stronger oxidizing agent than Cu2+^ (and Cu is a stronger reducing agent than Zn). That is, a redox reaction will occur spontaneously to produce the weaker oxidizing and reducing agents.
A standard oxidation-reduction potential series (standard potential series) is a list of reduction half-reactions. The half-reactions are listed such that the reduction half-reaction for the strongest oxidizing agent is written first, followed by the next strongest, and so on. Since the strongest oxidizing agent produces the weakest reducing agent, as you proceed down the right side (product side) of the series, the reducing agents will be progressively stronger, as shown on the next page.
Oxidation-Reduction Potential Series
oxidizing reducing agents agents
stronger oxidizing agent reactant + e- → product weaker reducing agent reactant + e- → product reactant + e- → product reactant + e- → product reactant + e- → product reactant + e- → product reactant + e- → product reactant + e- → product reactant + e- → product weaker oxidizing agent reactant + e- → product stronger reducing agent
reduction half-reactions
In this experiment you will use experimental evidence and additional information to write a potential series for some cations, halogens, and hydrogen ion.
On your report sheet incorporate silver ion, copper (II), and zinc ion into a potential series ions so that your oxidation-reduction potential series consists of reduction half-reactions for all three metal cations listed in order such that the reaction of the strongest oxidizing agent is written first and the weakest last.
- Hydrogen, Silver, Copper, and Zinc
SAFETY CAUTION:
HYDROCHLORIC ACID SOLUTION: POISON! CORROSIVE. LIQUID AND MIST CAUSE
SEVERE BURNS TO BODY TISSUE. MAY BE FATAL IF SWALLOWED OR INHALED.
Add a piece of each metal, silver, copper, and zinc, to 6 M hydrochloric acid solution in separate wells of a spot plate.
Examine each reaction mixture and record your observations on the Report Sheet. If you conclude from your observations that a reaction has occurred, write its net ionic equation.
DISPOSAL: Dispose of reaction mixtures (pieces of unreacted metals plus solutions) on spot plate by pouring them all into the proper waste container labeled “Ag and metals.”
On your report sheet incorporate hydrogen ion into the potential series for silver ion, copper (II) ion, and zinc ion, so that your oxidation-reduction potential series consists of reduction half-reactions for all five species listed in order such that the reaction of the strongest oxidizing agent is written first and the weakest last.
B. Potential Series for Halogens and Iron
- Chlorine, Bromine, and Iodine
In this section of the experiment water or an aqueous solution will be added cyclohexane, a nonpolar solvent. (The cyclohexane is not a reactant, just another solvent like water). From your observations of the colors of the halides and the halogens in the two solvent layers, you will determine whether a reaction has occurred or not.
SAFETY CAUTION:
CYCLOHEXANE: EXTREMELY FLAMMABLE LIQUID AND VAPOR. VAPOR MAY CAUSE
FLASH FIRE. HARMFUL OR FATAL IF SWALLOWED. HARMFUL IF INHALED. CAUSES IRRITATION
TO SKIN, EYES, AND RESPIRATORY TRACT.
CHLORINE WATER : CORROSIVE. CAUSES EYE AND SKIN BURNS. CAUSES
DIGESTIVE AND RESPIRATORY TRACT BURNS.
BROMINE WATER: CORROSIVE. CAUSES EYE AND SKINBURNS. CAUSES
DIGESTIVE AND RESPIRATORY TRACT BURNS.
IODINE WATER: POISON! CAUSES SEVERE IRRITATION OR BURNS TO EVERY AREA
OF CONTRACT. MAY BE FATAL IF SWALLOWED OR INHALED. VAPORS CAUSE SEVERE
IRRITATION TO SKIN, EYES, AND RESPIRATORY TRACT. OXIDIZER. MAY CAUSE ALLERGIC
SKIN OR RESPIRATORY REACTION.
POTASSIUM BROMIDE: HARMFUL IF SWALLOWED OR INHALED. MAY CAUSE IRRITATION TO
SKIN, EYES, AND RESPIRATORY TRACT.
POTASSIUM IODIDE: MAY CAUSE IRRITATION TO SKIN, EYES, AND RESPIRATORY
TRACT.
PART B IS TO BE CARRIED OUT IN THE HOOD.
All volumes are to be approximated.
a. Colors of Bromine, Chlorine, and Iodine in Both Cyclohexane and Water
Add 1 mL of cyclohexane to 2 mL of water in a 4-inch test tube. To the same test tube, add 1 mL bromine water (aqueous solution of bromine). Mix well. On your report sheet record the colors of both solvent layers. To a second 4-inch test tube, add 2 mL of water, 1 mL of cyclohexane, and 1 mL chlorine water (aqueous solution of chlorine). Mix well and record the colors of both solvent layers. To a third 4-inch test tube, add 2 mL of water, 1 mL of cyclohexane, and 1 mL iodine water (0.05 M I 2 in dropper bottle). Mix well and record the color of the cyclohexane layer. Now you will be able to identify any of these three halogens in the cyclohexane layer.
b. Potassium Bromide and Chlorine
Put 2 mL of 0.1 M aqueous potassium bromide solution in a 4-inch test tube and add 1 mL of cyclohexane. Mix well. Observe the colors of the two layers and record them on your report sheet.
To the test tube with aqueous potassium bromide/cyclohexane add 1 mL of Cl 2 water. Mix well Mix well and record the color of the cyclohexane layer. Now you will be able to identify any of these three halogens in the cyclohexane layer If you conclude from your observations that a reaction has occurred, write its net ionic equation.
c. Potassium Bromide and Iodine
Put 2 mL of 0.1 M aqueous potassium bromide solution in a 4-inch test tube and add 1 mL of cyclohexane. Mix well.
To the test tube with of aqueous potassium bromide/cyclohexane add 1 mL of I 2 water. Mix well. Mix well and record the color of the cyclohexane layer. Now you will be able to identify any of these three halogens in the cyclohexane layer If you conclude from your observations that a reaction has occurred, write its net ionic equation.
d. Potassium Iodide and Bromine
Write your observations on your report sheet. If a reaction occurred, write its net ionic equation.
Put 2 mL of 0.1 M aqueous potassium iodide solution in a 4 inch test tube and add 1 mL of cyclohexane. Mix well. To the test tube with aqueous KI/cyclohexane add 1 mL of Br 2 water. Mix well. Mix well and record the color of the cyclohexane layer. Now you will be able to identify any of these three halogens in the cyclohexane layer. If you conclude from your observations that a reaction has occurred, write its net ionic equation.
e. Potassium Iodide and Chlorine
Put 2 mL of 0.1 M aqueous potassium iodide solution in a 4 inch test tube and add 1 mL of cyclohexane. Mix well.
To the test tube with aqueous potassium iodide/cyclohexane add 1 ml of Cl 2 water. Mix well Mix well and record the color of the cyclohexane layer. Now you will be able to identify any of these three halogens in the cyclohexane layer. If you conclude from your observations that a reaction has occurred, write its net ionic equation.
Report - OXIDATION-REDUCTION EXPERIMENT
Chem 112
Name _________________________ Date ______Lab Section__________ Instructor’s Initials________________
A. Potential Series for Metals and Hydrogen
- Reactions of Copper and Zinc
a. Observations and reactions
(1) Copper + zinc nitrate Observations: _________________________________________________ Net ionic equation: _____________________________________________ (2) Zinc + copper (II) nitrate Observations: _________________________________________________ Net ionic equation: _____________________________________________ b. Relative oxidizing strengths Which is the stronger oxidizing agent? Cu2+^ or Zn2+^ _________
- Reactions of Silver with Copper and Zinc a. Observations and reactions (1) Copper + silver nitrate Observations: __________________________________________________ Net ionic equation: ______________________________________________ (2) Zinc + silver nitrate Observations: __________________________________________________ Net ionic equation: ______________________________________________
b. Potential Series for Cu2+, Zn2+, and Ag+ SOA WRA
WOA SRA
- Reactions of Hydrogen with Copper, and Zinc
a. Observations and reactions (1) Copper + hydrochloric acid Observations: ____________________________________________________ Net ionic equation: ________________________________________________ (2) Zinc + hydrochloric acid Observations: ____________________________________________________ Net ionic equation: ________________________________________________ (3) Silver + hydrochloric acid Observations: ____________________________________________________ Net ionic equation: ________________________________________________
b. Potential Series for Cu2+, Zn2+, Ag+, and H+ SOA WRA
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WOA SRA
Potential Series for Cl 2 , Br 2 , and l 2 SOA WRA
WOA SRA
- Bromine, Iodine, and Iron
a. Iron (lll) Chloride and Potassium Bromide Observations: _____________________________________________________
Net ionic equation: _________________________________________________
b. Iron (lll) Chloride and Potassium Iodide Observations: _____________________________________________________
Net ionic equation: _________________________________________________
Potential Series for Cl 2 , Br 2 , l 2 , and Fe3+
SOA WRA
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WOA SRA
C. Potential Series
SOA WRA
WOA SRA
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- Imagine that the hypothetical elements, A, B, C, and D, form the ions A2+, B2+, C2+, and D2+, respectively. The following equations indicate reactions which can, or cannot, occur. Use this information to write a potential series for the cations.
B2+^ + A → A2+^ + B B2+^ + D → N.R. A2+^ + C → C2+^ + A
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- Summarize the results of this experiment. Include the important principles and relationships that have been illustrated by this experiment.
