How to determine Acidic and Alkaline Buffer Solutions - Ionic Equilibria

In this video we want to discuss Buffer Solutions.
1. Definiton of a Buffer Solution
We know that a buffer solution is one that maintains pH when small amounts of H+ or OH- is added to it.
This means that inside this buffer, the following components must be present:
- an acid to remove OH-
- a base to remove H+
This mixture of acid and base must be of a conjugate acid-base pair, otherwise the acid and base will neutralise each other in the same solution.
2. Acidic Buffer
An acidic buffer is a mixture of weak acid and salt of conjugate base.
An example is a mixture of CH3COOH and CH3COONa.
For this mixture of conjugate acid-base pair:
- CH3COOH is the acid that removes OH-
- CH3COO- is the base that removes H+
We can show how H+ and OH- is removed via neutralisation reactions:
Since H+ and OH- is removed, therefore pH is maintained.
3. Alkaline Buffer
An alkaline buffer is a mixture of weak base and salt of conjugate acid.
An example is a mixture of NH3 and NH4Cl.
For this mixture of conjugate acid-base pair:
- NH4+ is the acid that removes OH-
- NH3 is the base that removes H+
We can show how H+ and OH- is removed via neutralisation reactions:
Since H+ and OH- is removed, therefore pH is maintained.
For the detailed step-by-step discussion on how an acidic and alkaline buffer work, check out this video!
Topic: Ionic Equilibria, Physical Chemistry, A Level Chemistry, Singapore
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[@illayathalapathyvijay6954]

Nice useful explanation sir tq for such an elaborate lesson

[@ChemistryGuru]

Hi Vijay thank you for your kind words! Glad you found the lesson useful! :)

[@ChemistryGuru]

Thanks Vijay! :)

[@tixt3m308]

Simplicity to its perfection 💯

[@hero4fun560]

ive been doing this topic blindly not knowing wat the concept really is, this video has great explanation of the idea.... KEEP IT UP GURU

[@ChemistryGuru]

Hi Saitama (:P) glad you found this useful! :)

[@yonkaiten_axel4237]

Thank you soooooooo much!! it's very useful and easy to understand

[@robinsonobaro4662]

I love ur explanation!!!

[@enricotortelli3642]

Very clear explanation!

[@ChemistryGuru]

Thanks Torta glad you found it useful! :)

[@mansoorabdulsattar7099]

Good. Can we use tri sodium phosphate for alkaline buffer

[@holyravenification]

Hey there i have a question hope my English d be enough for asking.
Lets say we have 1M ch3cooh and 1M ch3cooNa together, that calls acidic buffer right. i know how to calculate ph with handerson equation but i don't understand the chemical foundation of this situation. We have a weak acid ch3cooh and its pair base ch3coo- which is stronger than ch3cooh. Than how come the solutuon is acidic??

[@ChemistryGuru]

The conjugate base of a weak acid is not strong. Weak acid will always dissociate to give weak conjugate base since the dissociation is reversible. If the conjugate base were strong, it will force the reaction to completion and there will no longer be any equilibrium.
Similarly, a weak acid does not mean its conjugate base must be stronger. To compare strength of weak acid ethanoic acid and its conjugate base, we can look at their equilibrium constants.
Ka for ethanoic acid = 1.74 x 10^-5
Kb for ethanoate = Kw / Ka = 5.75 x 10^-10
Since Ka for ethanoic acid is greater, it will dissociate and give more H+ in solution as compared to ethanoate dissociating in solution to give OH-
So a mixture of ethanoic acid + ethanoate is acidic and considered an acidic buffer.

[@holyravenification]

@@ChemistryGuru thank you so much so if we have an acid which has ka around 10^-10 and its salt we can have basic solution too. am i right?

[@ChemistryGuru]

@@holyravenification yes if the Kb for the conjugate base is greater than Ka for acid then mixture of equal concentration of acid + conjugate base should be basic.