ELECTROCHEMISTRY
[UNIT 4]
MST_CREATOR
Tumblr, Instagram, Twitter, NG, DeviantArt, and itch.io
Table of Contents
Note From Author ..................................................................................................................................... 2
Electrolysis .................................................................................................................................................... 3
Electrolytic Cells ..................................................................................................................................... 3
About The Graphite Rods… ............................................................................................................ 3
About The Liquid…............................................................................................................................. 4
Transfer of Charge ............................................................................................................................ 4
Electrolysis of Lead (II) Bromide ...................................................................................................... 4
The Bulb Throughout the Experiment ....................................................................................... 5
Binary Compounds ............................................................................................................................ 5
Some Chemical Equations ............................................................................................................... 5
Electrolysis of Dilute Sulfuric Acid .................................................................................................. 6
What’s the Difference? ..................................................................................................................... 6
What Goes Where?............................................................................................................................. 6
The Electrolysis (Finally).................................................................................................................. 7
Electrolysis of Concentrated Aqueous Sodium Chloride ......................................................... 8
How We Decide ................................................................................................................................... 8
Reactions................................................................................................................................................ 8
Electrolysis of Aqueous Copper (II) Sulfate .................................................................................. 9
Reactions................................................................................................................................................ 9
The Setup .............................................................................................................................................. 9
The Electrolysis Rules......................................................................................................................... 10
Electroplating ........................................................................................................................................... 10
Plating Bath .......................................................................................................................................... 10
MST_Creator
Page 1
Tumblr, Instagram, Twitter, NG, DeviantArt, and itch.io
Plating a Spoon with Silver ............................................................................................................ 11
At The Spoon… ................................................................................................................................ 11
Hydrogen-Oxygen Fuel Cells............................................................................................................... 12
How They Work ................................................................................................................................... 12
Reactions............................................................................................................................................. 12
Advantages & Disadvantages ............................................................................................................. 13
Note From Author
Hey guys!
Sorry I never updated the website, I had exams (mocks).
To be honest, I seriously messed up economics and computer science ☹
I literally decided to answer ALL 5 questions in section B for some reason…
For computer science, well I had accounting right before CS so yeah, recipe for
disaster lol.
Anyways, now that I have winter break, you can expect notes for the other subjects
coming in soon!
(Going to do unit 2 for econ now)
MST_Creator
Page 2
Tumblr, Instagram, Twitter, NG, DeviantArt, and itch.io
Electrolysis
Electrolysis is the breakdown of an ionic compound, molten or in aqueous solution,
using electricity.
Electrolytic Cells
About The Graphite Rods…
In the electrolytic cell, we have 2 charged graphite rods.
These graphite rods are called “electrodes”, an electrode can be defined as:
“A point where the electric current enters or leaves a batter or
electrolytic cell.”
Inert electrodes can be made of graphite, carbon, or platinum.
There are 3 types of electrodes:
1. Inert Electrode: these do not react with the products of electrolysis.
2. Anode: these are positively charged electrodes where oxidation happens..
3. Cathode: these are negatively charged electrodes where reduction happens.
MST_Creator
Page 3
Tumblr, Instagram, Twitter, NG, DeviantArt, and itch.io
About The Liquid…
The liquid in the electrolytic cell can either contain electrolytes or non-electrolytes.
Electrolytes are ionic compounds which conduct electricity in their molten or aqueous
state, but not in their solid state.
Non-electrolytes are liquids or solutions which do not take part in electrolysis as the
do not contain ions.
Transfer of Charge
The transfer of charge in electrolysis is by:
1. The movement of electrons in the graphite or metallic electrodes.
2. The loss or gain of electrons from the external circuit at the electrodes.
3. The movement of ions in the electrolyte.
Electrolysis of Lead (II) Bromide
The molten Lead (II) Bromide splits up into ions and goes to their respective
electrodes.
The Lead ions collect at the cathode and undergo reduction to become Lead atoms.
The Bromine ions collect at the anode, undergo oxidation to become Bromine atoms
which are then released into the air as gas.
MST_Creator
Page 4
Tumblr, Instagram, Twitter, NG, DeviantArt, and itch.io
The Bulb Throughout the Experiment
Let’s say that the molten Lead (II) Bromide was solid, when this is the case, the bulb
would not turn on as it does not allow electricity to pass through.
After heating the solid Lead (II) Bromide and turning it into molten Lead (II)
Bromide (as shown in the figure), the bulb lights up.
This is because the molten PbBr2 now acts as an electrolyte.
Binary Compounds
Lead (II) Bromide is a compound known as a “binary compound”.
A binary compound is a compound which contains 2 chemically combined elements.
Some Chemical Equations
Main Equation
𝑀𝑜𝑙𝑡𝑒𝑛 𝐿𝑒𝑎𝑑 (𝐼𝐼) 𝐵𝑟𝑜𝑚𝑖𝑑𝑒 → 𝐿𝑒𝑎𝑑 + 𝐵𝑟𝑜𝑚𝑖𝑛𝑒 𝐺𝑎𝑠
𝑃𝑏𝐵𝑟2 (𝑙) → 𝑃𝑏(𝑙) + 𝐵𝑟2 (𝑔)
This is a decomposition reaction.
Reaction at Cathode
𝐿𝑒𝑎𝑑 𝐼𝑜𝑛 + 𝑒𝑙𝑒𝑐𝑡𝑟𝑜𝑛𝑠 → 𝐿𝑒𝑎𝑑 𝐴𝑡𝑜𝑚
−
𝑃𝑏2+
(𝑙) + 2𝑒 → 𝑃𝑏(𝑙)
This is a reduction half-equation.
Remember that cations go to the cathode.
Reaction at Anode
𝐵𝑟𝑜𝑚𝑖𝑑𝑒 𝐼𝑜𝑛 → 𝐵𝑟𝑜𝑚𝑖𝑛𝑒 𝐴𝑡𝑜𝑚 + 𝑒𝑙𝑒𝑐𝑡𝑟𝑜𝑛
−
2𝐵𝑟−
(𝑙) → 𝐵𝑟2 (𝑔) + 2𝑒
This is an oxidation half-equation.
Remember that anions go to the anode.
MST_Creator
Page 5
Tumblr, Instagram, Twitter, NG, DeviantArt, and itch.io
Electrolysis of Dilute Sulfuric Acid
Some Information
Electrode Material
Platinum
Ions
H+, OH-, and SO42-
What’s the Difference?
Well, here, instead of having only one compound splitting into ions, you got 2 unlike
how it was in our previous example with lead (II) bromide.
This now raises another question; how do we know what goes where?
What Goes Where?
Let me elaborate, in the example with molten lead (II) bromide, we knew where the
ions would go, and which ones would go where.
However, since there are 2 compounds splitting up, we would not know which ions
would collect at the anode and which ones would collect at the cathode and which
ones would be left behind in the solution.
Selective Discharge of Ions
This is a table of some ions and how
easily they discharge.
We can use this table to determine
which ions are left behind in the solution
and which ones collect at the electrodes.
MST_Creator
Page 6
Tumblr, Instagram, Twitter, NG, DeviantArt, and itch.io
The Electrolysis (Finally)
Since there is only one cation (H+), we see hydrogen ions collect at the cathode.
However, since there are 2 anions, we must refer to the selective discharge of ions
table to know which collects at the anode and which is left behind.
On the table, we see that OH- ions discharge more easily than SO42- ions.
This means that OH- ions collect at the anode and the SO42- ions are left behind.
Reactions
At The Anode:
𝐻𝑦𝑑𝑟𝑜𝑥𝑖𝑑𝑒 𝐼𝑜𝑛𝑠 → 𝑊𝑎𝑡𝑒𝑟 + 𝑂𝑥𝑦𝑔𝑒𝑛 + 𝐸𝑙𝑒𝑐𝑡𝑟𝑜𝑛𝑠
−
4𝑂𝐻−
(𝑎𝑞) → 2𝐻2 𝑂(𝑙) + 𝑂2 (𝑔) + 4𝑒
At The Cathode:
𝐻𝑦𝑑𝑟𝑜𝑔𝑒𝑛 𝐼𝑜𝑛𝑠 + 𝐸𝑙𝑒𝑐𝑡𝑟𝑜𝑛𝑠 → 𝐻𝑦𝑑𝑟𝑜𝑔𝑒𝑛 𝐺𝑎𝑠
−
4𝐻+
(𝑎𝑞) + 4𝑒 → 2𝐻2 (𝑔)
What if We Had Graphite Electrodes?
For this experiment, we used platinum electrodes but the question “what happens if
we use graphite electrodes?” arises.
Well, the outcome will remain the same. However, there may be small amount of
Carbon Dioxide which would be produced along with the Oxygen at the anode.
MST_Creator
Page 7
Tumblr, Instagram, Twitter, NG, DeviantArt, and itch.io
Electrolysis of Concentrated Aqueous Sodium
Chloride
Some Information
Electrode Material
Platinum/Graphite/Carbon
Ions
H+, OH-, Na+, and Cl-
Ions at Anode
Cl-
Ions at Cathode
H+
How We Decide
At Anode
At Cathode
After looking at the image of selective
After looking at the image of selective
discharge of ions, we see that the Cl-
discharge of ions, we see that the H+ ions
ions give up electrons easier than
accept electrons easier than Na+ ions.
OH- ions.
This means that Hydrogen collects at the
This means that Chlorine collects at the
cathode.
anode.
Reactions
At Anode
At Cathode
𝐶ℎ𝑙𝑜𝑟𝑖𝑛𝑒 𝐶ℎ𝑙𝑜𝑟𝑖𝑛𝑒
→
+ 𝐸𝑙𝑒𝑐𝑡𝑟𝑜𝑛𝑠
𝐼𝑜𝑛𝑠
𝐺𝑎𝑠
𝐻𝑦𝑑𝑟𝑜𝑔𝑒𝑛
𝐻𝑦𝑑𝑟𝑜𝑔𝑒𝑛
+ 𝐸𝑙𝑒𝑐𝑡𝑟𝑜𝑛𝑠 →
𝐼𝑜𝑛𝑠
𝐺𝑎𝑠
−
2𝐶𝑙−
(𝑎𝑞) → 𝐶𝑙2 (𝑔) + 2𝑒
−
2𝐻+
(𝑎𝑞) + 2𝑒 → 𝐻2 (𝑔)
MST_Creator
Page 8
Tumblr, Instagram, Twitter, NG, DeviantArt, and itch.io
Electrolysis of Aqueous Copper (II) Sulfate
Some Information
Electrode Material
Platinum/Graphite/Carbon
Ions
H+, OH-, Cu2+, and SO42-
Ions at Anode
OH-
Ions at Cathode
Cu2+
Reactions
At Anode
At Cathode
𝐻𝑦𝑑𝑟𝑜𝑥𝑖𝑑𝑒
→ 𝑊𝑎𝑡𝑒𝑟 + 𝑂𝑥𝑦𝑔𝑒𝑛 + 𝐸𝑙𝑒𝑐𝑡𝑟𝑜𝑛𝑠
𝐼𝑜𝑛𝑠
−
4𝑂𝐻(𝑎𝑞)
→ 2𝐻2 𝑂(𝑙) + 𝑂2 (𝑔) + 4𝑒 −
𝐶𝑜𝑝𝑝𝑒𝑟
𝐼𝑜𝑛𝑠
+ 𝐸𝑙𝑒𝑐𝑡𝑟𝑜𝑛𝑠 → 𝐶𝑜𝑝𝑝𝑒𝑟
−
𝐶𝑢2+
(𝑎𝑞) + 2𝑒 → 𝐶𝑢(𝑠)
The Setup
MST_Creator
Page 9
Tumblr, Instagram, Twitter, NG, DeviantArt, and itch.io
📝The Electrolysis Rules📝
1. Anions go to the anode.
2. Cations go to the cathode.
3. Non-metals are produced at the anode.
4. Metals & Hydrogen gas are produced at cathode.
5. At an inert anode, the halogens are produced in preference to Oxygen.
6. At an inert cathode, Hydrogen gas is produced in preference to metals unless any
unreactive metals are present.
7. When there are more than 2 compounds being electrolysed, refer to the image of
selective discharge of ions.
Electroplating
Electroplating is the process where we use electrolysis to coat or plate on metal
object with a layer of another metal.
Electroplating is used to improve an object’s appearance (to make it look pretty) or
give protection to the metal object beneath (to increase resistance to corrosion).
Plating Bath
This is the electrolytic cell where we carry out the electroplating process.
The electrolytic cell that we use for electroplating is slightly different to the
electrolytic cell we saw in the start of this document.
The only difference is that we have a different cathode, the cathode is quite literally,
the metal object we are plating.
MST_Creator
Page 10
Tumblr, Instagram, Twitter, NG, DeviantArt, and itch.io
Plating a Spoon with Silver
At The Spoon…
MST_Creator
Page 11
Tumblr, Instagram, Twitter, NG, DeviantArt, and itch.io
Hydrogen-Oxygen Fuel Cells
These are fuel cells which only use Hydrogen and Oxygen to produce electricity with
water as the only substance produced.
How They Work
The electrodes are porous to allow the transfer of O2, H2, and H2O.
There is a NaOH electrolyte present between the 2 electrodes.
Reactions
At Anode
At Cathode
𝐻𝑦𝑑𝑟𝑜𝑔𝑒𝑛 𝐻𝑦𝑑𝑟𝑜𝑥𝑖𝑑𝑒
+
→ 𝑊𝑎𝑡𝑒𝑟 + 𝑒𝑙𝑒𝑐𝑡𝑟𝑜𝑛𝑠
𝐺𝑎𝑠
𝐼𝑜𝑛𝑠
𝑂𝑥𝑦𝑔𝑒𝑛
𝐻𝑦𝑑𝑟𝑜𝑥𝑖𝑑𝑒
+ 𝑊𝑎𝑡𝑒𝑟 + 𝑒𝑙𝑒𝑐𝑡𝑟𝑜𝑛𝑠 →
𝐺𝑎𝑠
𝐼𝑜𝑛𝑠
−
𝐻2 (𝑔) + 2𝑂𝐻−
(𝑎𝑞) → 2𝐻2 𝑂(𝑙) + 2𝑒
MST_Creator
𝑂2 (𝑔) + 2𝐻2 𝑂(𝑙) + 4𝑒− → 4𝑂𝐻−
(𝑎𝑞)
Page 12
Tumblr, Instagram, Twitter, NG, DeviantArt, and itch.io
Advantages & Disadvantages
Advantages
Disadvantages
Pollution free (water is the only
Hydrogen is difficult to store as it is a
product)
gas at room temperature/pressure
Similar to a battery which does not
Fuel cells are costly & expensive
need external charging
Can produce electricity as long as
Electric motors and fuel cells are not as
Hydrogen fuel & Oxygen are provided
durable as petrol/diesel engines
～(￣▽￣～)
MST_Creator
(p≧▽≦)p The End q(≧▽≦q) (～￣▽￣)～
Page 13