Water electrolysis with bases
To carry out the electrolysis of water in a basic environment and observe the different reactions.
Cosa imparano gli studenti
La scienza alla base di questo esperimento
This experiment shows the electrolysis of water using a different redox reaction. By changing the pH of the solution the reactions differ, although the results are the same.
In the basic environment there are OH – ions and Na+ ions, which migrate respectively towards the anode and cathode.
At the cathode, water molecules are reduced because their potential ( E0( H2O / H2 ) = – 0.83 V ) is greater than that of the sodium ions ( E0(Na / Na+ ) = – 2.73V ).Sodium ions will not undergo any reduction due to their very negative reduction potential.
At the anode OH – ions are oxidised because their potential (E0( O2 / OH ) = + 0.40 V) is lower than the potential of the redox couple ( E0( O2 / H2O ) = +1.23 v).
At the cathode (–) 4 H2O + 4 e – → 2 H2 + 4 OH –.
At the anode (+) 4 OH – → O2 + 2H2O + 4 e –.
Attrezzatura utilizzata
- U tube with side outlets — 1276.10
- Platinum electrodes — 4716.12
- Connecting wires, red — 2522.03-04
- Connecting wires, black — 2522.04-08
- DC power supply
Sostanze chimiche e reagenti
- Sodium hydroxide 0.2 M — R:35 S:26-37/39-45
Note sulla sicurezza
- Always wear protective goggles and gloves.
- Hydrogen and air mixtures are explosive. Make sure there are no naked flames near the apparatus.
Domande per gli studenti
- Describe what happens in the apparatus.
- Write the balanced equations of the process and record your observations.
- What happens on igniting the test tubes? State where hydrogen and oxygen are produced.
- What are the differences between electrolysis in a basic and an acidic environment?
Cosa aspettarsi
<p>Passage of the electric current causes bubbling at the electrodes.</p><p>The gas collected at the cathode () pops stating the presence of hydrogen.</p><p>The gas collected at the anode (+) brighten up the flame indicating the presence of oxygen.</p><p>The reactions in the basic environment involve OH – ions instead of H+.</p><p>At the cathode () water molecules are reduced producing OH– and hydrogen. At the anode (+) OH – ions are oxidised to oxygen and water.</p>
Smaltimento
Dispose of the solution into the waste container.
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Questo esperimento fa parte dell’ATP “ Mobile Lab ” — un laboratorio autonomo che trasforma una normale aula in un vero e proprio laboratorio scientifico, con oltre 200 esperimenti di fisica, chimica, biologia, robotica e ingegneria. “ Gali ”, il tutor basato sull’intelligenza artificiale integrato in ATP Connect, guida gli studenti in ogni fase e risponde alle loro domande direttamente al banco di lavoro.
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