Summary: Sodium sulfate solution is electrolyzed to make hyrogen and oxygen gas. A ignited wood stick shown to glow more brightly in the presence of concentrated oxygen gas (collected in a test tube). Hydrogen gas collected in a test tube is ignited using a bunsen burner.
Hazards:
Chemicals and Solutions:
1.0 M Sodium sulfate solution
Materials:
Electrolysis Apparatus
D.C. Power Supply
Dilute (0.5M or so) Na2SO4 solution. Phenolphthalein may be added to show formation of hydroxide ion at the cathode.
Splint
Matches
Testubes
Procedure:
Open stopcocks, making sure that the sodium sulfate solution filles each compartment to the tip. Close stopcocks. Attach apparatus to D.C. power supply.
Do a check to make sure the demo works.
As soon as class starts, turn on the power supply. Operate at about 10-12V.
Hydrogen may be collect at the cathode in a small test tube and ignited. Oxygen may be collected at the anode. Add a glowing splint to show that oxygen supports combustion.
Rinse apparatus immediately after use to avoid corrosion of the electrode.
Hint: Too much voltage will blow the Variac fuse, best to keep demo under ….
Sodium sulfate solution will eventually mould.
Discussion:
The overall reaction:
2H2O(l) ----> 2 H2(g)+ O2(g)
Reduction at the cathode:
Oxidation at the anode:
By multiplying the equation for the reaction at the cathode by two and then combining it to the equation for the reaction at the anode you get:
This equation can be simplified, because the H+ and the OH- combine to give water. You can then subtract 4H2O from each side to get:
To schedule a demonstration, please send an e-mail to the demonstration lab.
Contact:
Eric Camp
Lecture Demonstration Technician
Bagley Hall 171
(206) 543-1606