[CHEM] Chapter 4 - Electrolysis

1 DARRELL ER (COPYRIGHTED) © TOPIC 4: ELECTROLYSIS DARRELL ER (COPYRIGHTED) ©

2 CHAPTER ANALYSIS THE ABOUT TIME EXAM WEIGHTAGE • Very difficult chapter • 4 electrolytic cell set-up • 1 simple electric cell set-up • Usually tested in both MCQ & Paper 2 • Will need prior knowledge from other chapters: Oxidation & Reduction, Chemical Equations • Medium overall weightage • Constitute to 4% of marks for past 5 year papers DARRELL ER (COPYRIGHTED) ©

3 Chapter Overview MOLTEN ELECTROLYSIS & DILUTE ELECTRIC CELL SIMPLE ELECTRIC CELL This is probably one of the most difficult chapter in ‘O’ Level Chemistry. So let’s break down the chapter first before proceeding. CONCENTRATED - Only 2 ions present - Both ions will definitely be discharged - 4 ions present - Selectively discharge based on ease of discharge - 4 ions present - Cation follows normal ease of discharge - Anion follows ‘concentrated’ ease of discharge USING REACTIVE ELECTRODE - 4 ions present - Selectively discharged - Electroplating can occur if object is placed at cathode as metal cations would deposit itself onto the object - Use chemical reaction to produce electricity - Require 2 metals of differing reactivity - Does not require electric source DARRELL ER (COPYRIGHTED) ©

4 ELECTROLYTIC CELL MOLTEN IONIC COMPOUND AQUEOUS IONIC COMPOUND CONCENTRATED IONIC COMPOUND ELECTROPLATING All of the 4 scenarios falls under electrolytic cell. Let’s aim to get our basics right! KEY CONCEPT DARRELL ER (COPYRIGHTED) ©

5 ELECTROLYTIC CELL ELECTROLYTIC CELL An electrolytic cell is the set-up used for electrolysis. Key components: Electrolyte is the ionic compound, either in its molten or aqueous state, that would dissociate into ions when a current is passed through it. Electrodes are made of a conductive material. For inert electrodes, it is usually made of lead or platinum. Anode is the positively-charged electrode that is connected to the positive terminal of the electrical source. (Anode is positively charged & attracts anions, hence its called ‘anode’.) Cathode is the negatively-charged electrode that is connected to the negative terminal of the electrical source. (Cathode is negatively charged & attracts cations, hence its called ‘cathode’.) Battery/power source causes electrons to always flow from the anode to the cathode. (For those who take physics, under ‘electricity’, recall that electron flow is from the negative terminal to the positive terminal of the battery.) DARRELL ER (COPYRIGHTED) ©

6 ELECTROLYTIC CELL ELECTROLYTIC CELL Anode is the positively-charged electrode, as it is connected to the positive terminal of the battery. During electrolysis, anions are attracted to the positively charged anode. Anions are negatively charged and are looking to lose electrons to become neutral. Hence, as anions lose electrons at th