Electrolysis lab
Electrolyse molten and aqueous compounds, watch which ions are discharged, collect the gases, plate and purify copper, then build simple cells and measure E°cell.
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Learning objectives
- describe electrolysis as the conduction of electricity through an ionic compound (an electrolyte), when molten or dissolved in water, leading to chemical changes (including decomposition) at the electrodes
- describe electrolysis as evidence for the existence of ions which are held in a lattice when solid but which are free to move when molten or in solution
- describe, in terms of the mobility of ions present and the electrode products, the electrolysis of molten sodium chloride, using inert electrodes
- predict the likely products of the electrolysis of a molten binary ionic compound using inert electrodes
- apply the idea of selective discharge based on — cations: linked to the reactivity series (see also 8.4)
- apply the idea of selective discharge based on — anions: halides, hydroxides and sulfates (e.g. aqueous copper(II) sulfate and dilute sodium chloride solution (as essentially the electrolysis of water))
- apply the idea of selective discharge based on — concentration effects (as in the electrolysis of concentrated and dilute aqueous sodium chloride) (in all cases above, inert electrodes are used)
- predict the likely products of the electrolysis of an aqueous electrolyte, given relevant information
- construct ionic equations for the reactions occurring at the electrodes during the electrolysis, given relevant information
- describe the electrolysis of aqueous copper(II) sulfate with copper electrodes as a means of purifying copper (no technical details are required)
- describe the electroplating of metals, e.g. copper plating, and state one use of electroplating
- describe the production of electrical energy from simple cells (i.e. two electrodes in an electrolyte) linked to the reactivity series (see also 8.4) and redox reactions (in terms of electron transfer)
- Standard Electrode Potentials and the SHE
- Cell Potentials and Spontaneity
- ΔG = −nFE
- Electrolysis Predictions and Faraday’s Law
Dilute sulfuric acid with carbon electrodes and a current of 1.0 A. Cations will move to the cathode and anions to the anode when it is switched on.
- Charge, Q = It
- 0 C
- n(e⁻) = Q/F
- 0 mol
- At the cathode
- —
- At the anode
- —
- Voltmeter
- 1.10 V
- Electrons flow
- left → right
- ΔG = −nFE
- −212 kJ/mol
Try this
0 of 4 doneSwitch on with a solid salt (heat off), then melt it and switch on again. (not done yet)
A solid ionic compound does not conduct: its ions are held in a lattice. Once molten, the ions are free to move to the electrodes.
Electrolyse dilute, then concentrated, sodium chloride. Compare the gas at the anode. (not done yet)
In dilute solution OH⁻ is discharged and oxygen forms (half the volume of hydrogen). In concentrated solution the many Cl⁻ ions are discharged instead, giving chlorine.
In copper(II) sulfate, record the cathode's gain in mass at three different charges. (not done yet)
The mass of copper is proportional to the charge: 2 mol of electrons (193 000 C) deposit 1 mol (63.5 g) of copper, whatever the current.
Build a simple cell that gives the largest voltage you can. (not done yet)
The further apart the metals are in the reactivity series, the larger the voltage. The more reactive metal is the negative electrode: it loses electrons.
Your readings
| # | I / A | t / s | Q / C | Δm(cathode) / g | Remove |
|---|---|---|---|---|---|
| No readings yet. Set up a measurement, then record it. | |||||