Weak Diprotic Acid Titration Curve

How to Sketch Titration Bend for Diprotic Acid

In this JC2 webinar we want to larn how to sketch titration curve for diprotic acrid.

Let's consider the titration of ethanedioic acrid (H₂C₂O₄) with sodium hydroxide.

A diprotic acrid will react with OH^- in two stages:

diprotic acid titration curve reactions

Each stage can be treated as a monoprotic acid-base of operations reaction.

First acid H₂C₂O_iv is stronger than second acid HC₂O₄ ^-, hence reaction 1 will go along first and go to completion before the second reaction volition outset.

At the end of each reaction, there will be an equivalence signal.

Therefore we accept 2 distinct reactions with 2 distinct equivalence points.

Here are the 3 points that we tin can apply for plotting:

1. Initial pH
ii. Maximum buffering capacity during reaction 1
iii. Maximum buffering chapters during reaction ii

one. Initial pH

For a diprotic acrid, we presume that the H⁺ only comes from the first dissociation of H₂C₂O₄.

The second acid HC_twoO₄ ^- is weaker and volition contribute an insignificant corporeality of H⁺.

So we tin can only care for a diprotic acrid like a monoprotic acid, and focus on its first dissociation.

Hence the weak acrid formula can be used to determine H⁺ concentration and pH.

diprotic acid titration curve initial pH

2. Maximum buffering capacity during reaction 1

During reaction 1, H₂C₂O₄ is in backlog and a buffer is formed.

This buffering system is made up of weak acrid H₂C₂O₄ and cohabit base HC₂O_four ^-.

diprotic acid titration curve buffer region for reaction 1

Hence we can determine its maximum buffering capacity for the commencement buffer region.

diprotic acid titration curve calculate max buffering capacity for reaction 1

Mbc is very useful to plot on a titration curve since gradient at that point is zero.

Therefore the shape of the graph at and effectually mbc will exist very well defined.

3. Maximum buffering capacity during reaction 2

Similarly, during reaction two, HC₂O₄ ^- is in excess and a buffer is formed.

This buffering arrangement is fabricated up of weak acid HC₂O_four ^- and conjugate base C₂O₄ ^two-.

diprotic acid titration curve buffer region for reaction 2

Hence we tin can determine its maximum buffering capacity for the second buffer region.

diprotic acid titration curve calculate max buffering capacity for reaction 2

Let'southward put everything together and plot our titration curve!

We tin can make employ of the maximum buffering capacities to depict the buffer regions for both reactions.

The range of rapid pH changes at both equivalence points tin then exist added.

diprotic acid titration curve sketch titration curve

With these 3 points we tin can sketch a very decent looking titration curve for diprotic acids.

Topic: Buffer and Titration Curve, Physical Chemistry, A Level Chemical science, Singapore

Back to other previous Physical Chemistry Video Lessons.

Found this A Level Chemistry video useful?

Please Like this video and SHARE it with your friends!

Join my 7000+ subscribers on myYouTube Channel for new A Level Chemistry video lessons every week.

Check out other A Level Chemistry Video Lessons here!

Demand an experienced tutor to make Chemical science simpler for you?

Do consider signing upwardly for my JC Chemistry Tuition classes at Bishan, weekly LIVE webinars or on-demand video lessons!