Electrochemistry: MCQ 3

The Electrochemical Series

• The electrochemical series is a table that shows metals arranged in order of their tendency to lose electrons.
• The more readily a metal loses electrons, the more reactive it is.
• Potassium is at the top of the electrochemical series, and gold is at the bottom.
• A metal will displace another metal below it in the electrochemical series from a solution of its salt.

Displacement Reactions

• Magnesium ribbon dipped in copper sulfate solution displaces copper ions from the solution.
• The displaced copper then coats the magnesium ribbon.
• Zinc becomes covered in copper metal because zinc is higher in the electrochemical series and displaces copper.

Electrolysis

• Electrolysis is the breaking up of a substance due to an electric current passing through it in an aqueous solution or when molten.
• Electrolysis requires electrodes and an electrolyte.
• An electrolyte is a substance that conducts electricity when dissolved in water or when molten.
• Electrolytes themselves become chemically changed during electrolysis.

Electrodes

• An electrode is a conductor connected to the positive or negative end of a battery.
• There are two types of electrodes: inert electrodes (e.g., graphite and platinum) and active electrodes (e.g., copper).
• An active anode electrode gradually dissolves as electricity is passed through the electrolyte.

Anode and Cathode

• Oxidation occurs at the anode (OIL), and reduction occurs at the cathode (RIG).
• Anions are attracted to the anode, while cations are attracted to the cathode.

Experiment to Demonstrate Ionic Movement

• Copper dichromate solution breaks up into Cu²⁺ cations and Cr₂O₇²⁻ anions during electrolysis.
• Cu²⁺ cations are attracted to the cathode, and Cr₂O₇²⁻ anions are attracted to the anode.

Electrolysis of Aqueous Sodium Sulfate

• Sodium sulfate solution and universal indicator are used.
• At the anode, O₂ gas is released, and H⁺ ions are present.
• At the cathode, OH⁻ ions are released, causing the indicator to turn blue.

Electrolysis of Aqueous Potassium Iodide

• Potassium iodide solution and phenolphthalein indicator are used.
• At the anode, I₂ is formed, resulting in a brown color.
• At the cathode, K⁺ ions are reduced.

Electrolysis of Acidified Water

• This is carried out using a Hoffman Voltameter.
• Water breaks up into H⁺ and OH⁻ ions.
• H⁺ ions are reduced at the cathode, resulting in H₂ gas.
• OH⁻ ions are oxidized at the anode, resulting in O₂ gas.

Electrolysis of Copper (II) Sulfate Solution

• Copper electrodes are used.
• At the anode, copper is oxidized, and Cu²⁺ ions are released into solution.
• At the cathode, Cu²⁺ ions are reduced, and solid copper is formed.

Electroplating

• This involves coating one inexpensive metal with another more expensive metal using electrolysis.
• Examples include coating nickel cutlery with silver and chrome plating of steel.