Electrolysis (I) LQ: What happens at the electrodes?

Learning outcomes I can describe electrolysis as the decomposition of an electrolyte with an electric current – Grade B I can describe the changes at the electrodes during electrolysis – Grade A I can (H) use ionic theory to explain the changes that take place at the electrodes – Grade A*

– Any molten or dissolved material in which the liquid contains free moving ions is called the electrolyte. – Ions are charged particles e.g. Zn 2+ sodium ion, or Cl – chloride ion, and their movement or flow constitutes an electric current, because a current is moving charged particles. – What does the complete electrical circuit consist of? There are two ion currents in the electrolyte flowing in opposite directions: – positive cations e.g. Zn2 + attracted to the negative cathode electrode, – and negative anions e.g. Cl – attracted to the positive anode electrode, – BUT remember no electrons flow in the electrolyte, only in the electrodes The circuit of 'charge flow' is completed by the electrons moving around the external circuit e.g. graphite electrode, from the positive to the negative electrode

I can describe electrolysis as the decomposition of an electrolyte with an electric current – Grade B What does “decomposition” mean? What is an “electrolyte”? Which electrode is the (a) metal ion and (b) non-metal ion attracted to How does the metal ion become a metal atom? How does the non-metal ion become a non-metal atom? How many electrons does (a) zinc gain and (b) chlorine lose? What happens to the (a) zinc (b) chlorine that is formed? Extension (A*): why are the zinc and chlorine atoms now called “neutral” atoms?

Revision Positive electrode – anode Negative electrode - cathode

I can describe the changes at the electrodes during electrolysis – Grade A Write a paragraph explaining what happens to the zinc ion and chloride ion during electrolysis Use the words: electrode (positive/negative), attracted, gain, lose electron(s), atom, gas, metal

Graded answers Grade CGrade BGrade A Zinc is attracted to the negative electrode Chlorine is attracted to the positive electrode Zinc metal is formed Chlorine gas is formed Zinc gains electronsZinc gains 2 electrons Chlorine loses electronsChlorine loses 1 electron Zinc atoms formedZinc atoms/metal at negative electrode Chlorine atoms formed2 chlorine atoms formed and form chlorine molecule Chlorine gas formed/released at positive electrode

Electrolysis of copper chloride

Electrolysis of copper - summary Grade B: write a paragraph to explain what happens to the copper and chlorine ions during electrolysis Ask Miss for help with questions Grade A: write a paragraph to explain what happens to the copper and chlorine ions during electrolysis

Graded answers Grade CGrade BGrade A Copper is attracted to the negative electrode Chlorine is attracted to the positive electrode Copper metal is formed Chlorine gas is formed Copper gains electronsCopper gains 2 electrons Chlorine loses electronsChlorine loses 1 electron Copper atoms formed at negative electrode Copper atoms/metal at negative electrode Chlorine atoms formed at negative electrode 2 chlorine atoms formed and form chlorine molecule Chlorine gas formed/released at positive electrode

Copper chloride Charges on copper and chloride ions? Which ion is attracted to which electrode? How many electrons are gained/lost by each ion? What happens to the atoms that are formed?

I can (H) use ionic theory to explain the changes that take place at the electrodes – Grade A* You can write ionic (half) equations to explain what happens to the ions at both electrodes In this ionic equation you must include electrons, as there is only one ion present: Zinc chloride: Zn e - Zn 2Cl - Cl 2 + 2e -

I can (H) use ionic theory to explain the changes that take place at the electrodes – Grade A* Use ionic theory to explain what happens at the positive and negative electrode during the electrolysis of copper chloride So…..write ionic equations for what happens to both copper and chloride ions at the respective electrodes

Sodium is extracted by the electrolysis of molten sodium chloride. 1. What are the two products of the process? 2. Use words and symbols to describe the changes at the electrodes during this process.

Sodium is extracted by the electrolysis of molten sodium chloride. 1. What are the two products of the process? Sodium and chlorine

2. Use words and symbols to describe the changes at the electrodes during this process. At the negative electrode: sodium ion + electron  sodium atom Na + + e –  Na At the positive electrode: chloride ion – electron  chlorine atom Cl – – e –  Cl chlorine atom + chlorine atom  chlorine molecule Cl + Cl  Cl 2