DEPARTMENT OF APPLIED CHEMISTRY
Industrial Inorganic Chemistry I
Doc No.
SCHPII - 2100
Experiment 1 –
Electrolysis
Electrolysis of water
Purpose
To produce H2 and O2 by electrolysis of an aqueous electrolyte
Introduction
Electrolysis is a process by which a chemical reaction is carried out by means of the passage
of an electric current. In the electrolysis of water, water is oxidized at the anode (negative)
and reduced at the cathode (positive). In some demonstrations, the cathode can be
recognized by a pink colour from the phenolphthalein indicator. Explain why this happens.
The electrodes will produce bubbles; however, the cathode can also be recognized due to
the greater production of gas. The gases produced at the electrodes can also be collected
and tested. A positive test for the presence of hydrogen is a soft pop sound when a burning
match is placed in the mouth of the container. The test for the presence of oxygen is to
place a smoldering match in the mouth of the container. If the match glows oxygen is
present.
Apparatus and Materials
Stainless Steel or Copper Electrodes
Copper Wires
Aqueous Electrolyte Solution
Distilled Water
DC Power Source
Timer/Stop watch
2x Graduated test tube/ burettes
Goggles
250cm3 beaker
Procedure
1. Clip a wire to one tip of each of the given electrodes.
2. Fill the beaker with 150ml electrolyte solution.
3. Invert the burettes into the beaker (make sure no air is inside the tubes by sucking
electrolyte with a pipette filler to the mark). The tubes can be held in place by
clamps.
4. Place an electrode inside each tube and attach the other ends of the wires to the
battery. (DO NOT LET THE WIRES OR ELECTRODES TOUCH EACH OTHER)
5. Start the stopwatch and observe the gas collecting at the top of the burettes.
6. Record the time per 0.5cm3 of gas produced for both electrodes.
7. After 20 min. disconnect the electrodes and test for the presence of H2 and O2
(procedure below).
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DEPARTMENT OF APPLIED CHEMISTRY
Industrial Inorganic Chemistry I
Doc No.
SCHPII - 2100
Test for H2 – Optional
1. Remove the leads from the battery
2. While holding a flaming splint, raise the base of the column slowly to the surface and
bring the splint to the mouth of the burette.
3. A soft pop sound or pale blue flame indicates hydrogen is present.
Test for O2
1. Remove the leads from the battery
2. While holding a glowing splint, open the tap of the column slowly
3. If the splint glows or relights then oxygen is present.
Data/ Results
Time
Volume of Hydrogen Gas/cm3
Volume of Oxygen Gas/cm3
Final Observed
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DEPARTMENT OF APPLIED CHEMISTRY
Industrial Inorganic Chemistry I
Doc No.
SCHPII - 2100
Volume
Pre – Lab Questions
1. What kind of a reaction is taking place? Write the equations for the reaction taking
place.
2. Why is the cathode indicated by a pink colour when phenolphthalein is added to the
solution? Use the equations to explain.
3. What are industrial applications of such kinds of reactions?
Post – Lab Questions
1. On the same axes plot graphs for the production of the oxygen and hydrogen gases
observed and comment on the ratios observed. Does it match the final volume of gas
collected?
2. Suggest the identity of electrolyte used this experiment? What is the use of an
electrolyte?
3. What are the sources of Error in this experiment? Suggest any method to make it
better.
4. Suggest any uses of the gases produced, particularly in Zimbabwe
5. Suggest better methods for such gases manufacture. Why was Electrolysis being out?
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