REDOX REACTIONS
E1
This exercise does not require a report.
PURPOSE
To observe common redox reactions.
BACKGROUND INFORMATION
Table 1.1 lists colours of some of the species involved in the reactions in this exercise. It should help
you identify the reaction products. Table 1.2 shows the common oxidation states of some elements
involved in the reactions in this exercise.
TABLE 1.1 Colours of selected substances
Species
Formula
Colour
Species
Formula
Colour
Permanganate
MnO4-
purple
Iodine
I2
red
Manganese dioxide
MnO2
brown ppte
Iodide
I-
colourless
Manganese (II)
Mn
2+
pale pink *
Iron (II)
Fe
2+
pale green *
Dichromate
Cr2O72-
orange
Iron (III)
Fe3+
pale yellow *
Chromate
CrO42-
yellow
Copper (II)
Cu2+
blue-green
2+
colourless
Chromium (III)
Cr
3+
green
Zinc (II)
Zn
* means that this will appear colourless in all but the most concentrated solutions
TABLE 1.2 Oxidation states of selected elements
Oxidation Number of Principal Element (in bold)
-3
-2
-1
0
+1
H2O
OH
H2O2
O 2 , H2
H
Cl2
ClO
-
Cl
2-
S
NH3
S
+2
+3
+4
+5
+6
+7
+
-
-
ClO4
2-
S2O3
-
N2
NO2
NO2
3+
2+
SO4
-
NO3
2-
Cr
Mn
2-
SO2
2SO3
CrO4
2Cr2O7
MnO2
2+
Zn
Zn
Cu
Cu
Fe
Fe
2+
2+
-
MnO4
3+
Fe
Some species you might not know
ClO- hypochlorite
ClO4- perchlorate
S2O32- thiosulfate
PROCEDURE
All the reactions below can be performed in test tubes. Obtain six test tubes and mark them A-F.
All volumes and masses do not need to be accurate. 1 mL = 1 Pasteur-pipette squirt.
I. Permanganate
Put 1 mL of 0.01 M KMnO4 into each of three test tubes.
Tube
A
Other reagents
Observations
1 mL 2.5 M H2SO4 then
2 mL of 0.1 M Fe (II)
B
2 mL of 0.1 M Fe (II)
C
1 mL 2.5 M H2SO4 then
2 mL of 0.1 M Fe (III)
II. Dichromate
Put 1 mL of 0.01 M K2Cr2O7 into two test tubes.
Tube
A
Other reagents
Observations
1 mL 2.5 M H2SO4 then
2 mL of 0.1 M Fe (II)
B
2 mL of 0.1 M Fe (II)
III. Hydrogen peroxide
Put 1 mL of diluted H2O2 and 1 mL 2.5 M H2SO4 into two test tubes.
A
1 mL of 0.01 M KMnO4 then
heat in a water bath
B
1 mL of 0.1 M KI
IV. Reaction of metals with metals
THIS MUST BE PERFORMED IN THE FUMEHOOD.
1.
2.
3.
Place a small piece of copper (5 mm x 5mm) in each of two test tubes.
Add 2 mL of concentrated HCl to one tube.
Add 2 mL of concentrated HNO3 to the other tube.
Heat the tubes in a steam bath ONLY if no reaction occurs within 30 seconds.
4.
5.
Place a piece of granulated zinc in and a piece of iron into separate test tube.
Add 2 mL of concentrated HCl to each tube.
Copper + HCl
Copper + HNO3
Iron + HCl
Zinc + HCl
V. Activities series of metals
A small piece of metal (5mm x 5mm) and 5 mL of solution (0.1 M) is sufficient here.
Metal
Solution
Cu
Zn2+
Zn
Cu2+
Cu
Fe2+
Fe
Cu2+
Zn
Fe2+
Fe
Zn2+
Observation
QUESTIONS
1.
Write equations for all reactions observed in this Exercise.
2.
Place the three metals in Parts IV and V (Cu, Zn, Fe) in order of reactivity.
3.
Where does hydrogen fit into the activity series in Q2?