Electrochemistry HL
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G. Galvin
Name:
Electrochemistry
Objectives
20. Electrochemistry
-explain what happens at each electrode during the electrolysis of:
•copper sulfate solution with copper electrodes
•acidified water with inert electrodes (half equations only required)
-describe and account for the observations of what happens at each electrode
during the electrolysis of (teacher demo)
•aqueous sodium sulfate (using universal indicator)
•aqueous potassium iodide (using phenolphthalein indicator) with inert electrodes
(half equations only required)
-describe the extraction of copper by displacements using scrap iron
-describe and explain ionic movement as observed during teacher demonstration
-describe the following electrolytic processes: purification of copper, chrome and nickel
plating. Give one everyday application of chrome and nickel plating e.g. cutlery
-arrange the electrochemical series of metals in order of their ease of oxidation
(reactions, other than displacement reactions, not required)
Defn: Electrolysis is the use of electricity to carry out a chemical reaction.
Electrolysis is carried out using a battery, electrodes and an electrolyte.
Battery: Provides energy for the reaction to occur.
Electrolyte: Aqueous solution containing dissolved ions so that it can conduct electricity
Electrodes: Anode: Positively charged electrode (connected to positive terminal of battery)
Cathode: Negatively charged electrode (connected to negative terminal of the battery)
Electrodes are usually made of carbon or platinum as they are inert
(unreactive).
Main events that occur during electrolysis:
1. Anode attracts negative ions (anions) from the electrolyte.
2. The energy from the battery allows the anions to lose electrons to the
anode. [OXIDATION of the anions]
3. The cathode attracts positive ions (cations) from the electrolyte.
4. The energy from the battery allows the cations to gain electrons from
the cathode [REDUCTION of the cations]
Experiment 1: Using electrolysis on a
solution of potassium iodide (KI) with
some added phenolphthalein using inert
electrodes
Observation: Brown colour around anode.
Pink colour around cathode.
Explanation: Anode: 2I- - 2e- I2 [I2 is red/brown in solution]
Cathode: 2H2O + 2e- H2 + 2OH- [OH- ions are basic, giving pink colour
………………………………………………………….in phenolphthalein]
