Understanding Electrolysis: Process, Reactions, and Examples, Lecture notes of Chemical Principles

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Electrolysis

Electrolysis

What type of compounds can be

electrolysed?

Electrolysis

“Ionic substances in

solution or in a melt can

be electrolysed.This is

because they contain

free moving ions.”

What type of compounds can be

electrolysed?

+ - Cl

• Cl

   Cl - 

Cl

Cl-^ Cl

Cl- Cl- positive electrode (anode) negative electrode (cathode) molten zinc chloride (ions free to move) Zn Zn2+ 2+ Zn 2+ Zn 2+ Zn2+ Zn2+ Zn 2+ Cl

+ - Zn 2+ Zn2+ Zn2+ Zn 2+ Cl- Cl

• Cl - Cl

Cl- Zn 2+ The positively charged zinc ions are attracted to the negative electrode

At the electrodes…

The ions in the molten liquid become atoms by either gaining or losing electrons.

At the CATHODE (-) Zinc ions each gain 2 electrons from the cathode (the electrons are pumped round the circuit from the powerpack) **Zn 2+

• 2 e**

-  Zn Silvery liquid White solid that melts to form dull white liquid

At the ANODE (+) Each chloride ion has 1 electron removed from it as soon as it touches the anode (the anode is like an “electron hoover”)

Cl

-

 Cl + e

**- Cl

ion 2,8, Cl atom 2,8, Electron flows up anode and back to powerpack to complete circuit** Because Chlorine atoms are only stable when they pair up, we usually double-up everything in the equation to give:

2Cl

-

 Cl

2

+ 2e

-

Anode (+) Cathode (-) Always non-metals Always oxidation ( LOSS of Electrons) Usually a gas Always metals or hydrogen Always reduction ( GAIN of electrons) Sometimes a solid (metal), sometimes bubbles (H 2

Some examples for you to try

1. Copper (II) Chloride
2. Nickel (II) Bromide
3. Zinc (II) Iodide Predict the product at each electrode and write the half-equations for each.

Answers

1. Copper (II) Chloride Anode -

Answers

1. Copper (II) Chloride Anode - Chlorine gas Cl 2