LQ: What happens at the electrodes?

• 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?

• Positive electrode – anode
• Negative electrode - cathode

• 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

Grade C
Zinc is attracted to the negative electrode
Chlorine is attracted to the positive electrode
Grade B
Zinc is attracted to the negative electrode
Chlorine is attracted to the positive electrode
Grade A
Zinc is attracted to the negative electrode
Chlorine is attracted to the positive electrode
Zinc metal is formed
Chlorine gas is formed
Zinc metal is formed
Chlorine gas is formed
Zinc gains electrons
Chlorine loses electrons
Zinc atoms formed
Chlorine atoms formed
Zinc metal is formed
Chlorine gas is formed
Zinc gains 2 electrons
Chlorine loses 1 electron
Zinc atoms/metal at negative electrode
2 chlorine atoms formed and form chlorine molecule
Chlorine gas formed/released at positive electrode

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

Grade C
Copper is attracted to the negative electrode
Chlorine is attracted to the positive electrode
Grade B
Copper is attracted to the negative electrode
Chlorine is attracted to the positive electrode
Grade A
Copper is attracted to the negative electrode
Chlorine is attracted to the positive electrode
Copper metal is formed
Chlorine gas is formed
Copper metal is formed
Chlorine gas is formed
Copper gains electrons
Chlorine loses electrons
Copper atoms formed at negative electrode
Chlorine atoms formed at negative electrode
Copper metal is formed
Chlorine gas is formed
Copper gains 2 electrons
Chlorine loses 1 electron
Copper atoms/metal 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 2+ + 2e 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