
Today, we shall take a look at the Tests for Oxidising Agents and Reducing Agents using common chemical reagents in our school laboratories.
Before we can continue, is important to first understand what is a Redox Reaction and how to identify one.
You will also need to know the definitions of Oxidising Agents and Reducing Agents.
A reducing agent is a substance that reduces another substance by:
- giving hydrogen to the substance
- removing oxygen from the substance
- giving electrons to the substance
In the process of reducing another substance, the reducing agent itself becomes oxidised.
Common Reducing Agents are:
- Potassium iodide, KI (colourless solution)
- Reactive metals such as Mg, Zn
- Hydrogen gas, H2
- Carbon, C
- Carbon monoxide, CO
- Hydrogen sulfide, H2S
- Sulfur dioxide, SO2
- etc
while
An oxidising agent is a substance that oxidises another substance by
- giving oxygen to the substance
- removing hydrogen from the substance
- receiving electrons to the substance
In the process of oxidising another substance, the oxidising agent itself becomes reduced. I have blogged about these agents before using the analogy of a property and an insurance agents.
Common Oxidising Agents are:
- Acidified potassium manganate (VII), KMnO4 (purple solution)
- Acidified potassium dichromate (VI), K2Cr2O7 (orange solution)
- Halogens e.g. Cl2, Br2
- Concentrated sulfuric acid, H2SO4
- Nitric acid, HNO3
- Oxygen, O2
- etc
In the video below, i will share with you on the step-by-step strategy to test for Oxidising and Reducing Agents using common laboratory reagents such as aqueous potassium iodide, KI(aq) and acidified potassium manganate (VII), KMnO4(aq) solutions.
Test for Oxidising Agent:
Use of a Reducing Agent e.g. aqueous potassium iodide, KI(aq)
Observation: Colourless solution turns brown
Chemistry behind it: 2I–(aq) => I2(aq) + 2e–
Test for Reducing Agent:
Use of an Oxidising Agent e.g. acidified potassium manganate (VII)
Observation: Purple solution decolourises
Chemistry behind it: MnO4–(aq) + 8H+(aq) + 5e– => Mn2+(aq) + 4H2O(l)
YouTube Video Tutorial
Let’s take a look at the YouTube Video now….
Length of video: 16.11 minutes
Direct video link: https://youtu.be/1YQsHwUrT2c
I hope you find the content easy for your understanding and if you have any questions, leave me a comment below. Feel free to share this blog post with your friends and learn the key O-Level Pure Chemistry concepts together.
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PS: Under related articles below, there are several blog post discussions and questions related to Redox Reaction concepts. You can also do a keyword search using the search box at the top right hand corner.

Hi Anas, good question.
Oxidising agents such as KMnO4 are strong oxidizing agent under any conditions but it is strongest and most powerful when it is in acidic conditions.
Let’s take at KMnO4 in different pH conditions:
Acidic solution: MnO4- + 8 H+ + 5 e- —> Mn(2+) + 4 H2O
Neutral solution: MnO4- + 4 H+ + 3 e- —> MnO2 + 2H2O
Basic solution: MnO4- + e- —> MnO4(2-)
As you can see from the above ionic half equations,
More electrons per MnO4- ion is involved (gained) in acidic solution (as compared to neutral solution and basic solution).
For these reasons, KMnO4 is a stronger oxidizing agent in acidic condition.
NOTE:
Depending on the syllabus that you are in, you may not know how to construct the above 3 ionic half equations.
This blog SimpleChemConcepts.com is primarily set up to help my local Singapore students taking the GCE O-Level Pure Chemistry and IP Chemistry examinations. They just need to know Basic Chemistry Principles.
Ionic half equations like those above are covered in my other Chemistry blog instead. You can visit http://www.ALevelH2Chemistry.com for more Advanced Chemistry Principles.
To learn how to write balanced redox equations, you can refer to the following blog posts:
https://www.alevelh2chemistry.com/?s=redox+equations
https://www.alevelh2chemistry.com/page/2/?s=redox+equations
Hope the above helps.
To Your Chemistry Success,
Sean Chua
Why are we using Acidified oxidising agents to test for reducing agents?
Wonderful
That’s great!
You can view more videos at https://www.SimpleChemConcepts.com/videos
Also, I did a sharing on practical exam tips at https://www.simplechemconcepts.com/tips-for-o-level-pure-chemistry-paper-3-practical-exam-2018/
I finally understand smth in chemistry!!!!! I’m sitting for my chem ‘O’ lvl practical exam tmr!!! I look forward to watching more!