Debye-Hückel Limiting Law

The Debye-Hückel limiting law provides a prediction for the activity coefficient of an ion in aqueous solution, which is valid in dilute solution.

[@cacabren]

Superb explanation! thank you for taking the time to teach this. I'm 2nd year Chemistry at Uni and was struggling!

[@PhysicalChemistry]

You're quite welcome. I'm glad you found it useful

[@jonathancruz5091]

As a biochemistry scientist, I’ve used this Debye-Huckel formula along side Henderson-Hasselbach equation to prove a certain mobile phase solution recipe was wrong in the lab I work at and how the pH range was not inline with the method stated.

[@abdulz2]

Another great lecture and how one can calculate the mean activity coefficient for a mixture of salt solution (brine )?

[@ErickCartman069]

Love your videos, finally i understand this law

[@PhysicalChemistry]

Great!

[@rekhapradhan1333]

Excellent explanation sir!.... It's help me so much!.... Thank you sir.

[@chemistrybysaadanwar]

Excellent excellent teaching sir

[@PhysicalChemistry]

Thanks, I appreciate it

[@zainabcassim6010]

I really understood the theory from your video. Thankyou very much. please do more on these..

[@PhysicalChemistry]

I'm glad you found it helpful

[@herteltm]

I generally enjoy your videos and have been incorporating some of your ideas, discussions, or examples into my own lectures. They have been incredibly helpful. However, there is a small error in this one. 1) Thanks to the DHLL, it is customary to plot (mean) activity coefficients versus √I. Therefore, in the lower of the two plots with γ vs. I, it should ideally display ln(γ) vs. √I. In that case, the initial linear slope would follow the DHLL equation. 2) In the plot as described in point 1), the initial slope for the 1:1 electrolyte should be half of the slope of the 2:1 electrolyte, as per the DHLL, which states that ln(γ) = - A |z_m z_p| √I. This is why the ln(γ) vs. √I plot is so useful. In the plot shown in this video, it seems that the two electrolytes have the same initial slope, which should not be correct, even if γ is plotted vs. I.

[@PhysicalChemistry]

Thanks, you're absolutely right. In the 2nd plot, I should have labeled the axes ln ɣ and √I, and the slope should be steeper for the CaCl₂ curve. I'll flag this comment so it will hopefully rise to the top and others can see the correction. Please flag any errors you spot in the other videos as well!

[@반두만]

Thx you,,,, u saved my test……

[@PhysicalChemistry]

I'm pretty sure you took the test yourself... But I'm glad you did well

[@반두만]

@@PhysicalChemistryDo you have another KZbin account for lectures?...!?!?

[@PhysicalChemistry]

@@반두만 No, all of the lectures I have recorded are on this channel

[@kayondejohn1598]

Aaha thanks very much Sir, I wish you make more videos, because KZbin is dominated by indians whose English I can't hear a word

[@PhysicalChemistry]

Don't worry, there are more videos to come. And I have plenty of comments from people telling me they have a hard time understanding me, so the more people / languages / accents posting PChem content, the better it is for everyone.

[@kayondejohn1598]

@@PhysicalChemistry ok am waiting for it's derivation, then I really also request that you make a video about calculation of pH using the Nernst equation 🙏

[@PhysicalChemistry]

@@kayondejohn1598 Interesting suggestion. The Nernst equation is usually taught in general and analytical chemistry (or quantitative analysis) in the US, so that isn't currently on my list of topics for PChem.

[@kayondejohn1598]

@@PhysicalChemistry ok sir. I thought it was the same as here in Uganda

[@PhysicalChemistry]

@@kayondejohn1598 I bet you can find some great Nernst equation videos of you search other chemistry channels. Good luck!

[@joyofliving5352]

hi sir, why is says that debye-huckle is only valid under low ionic strength? it is mentioned again and again but no simple explanation is given. can you address this pleasE?

[@tadeja1906]

Amazing explanation

[@PhysicalChemistry]

Thanks

[@sahhaf1234]

Excellent.. But when will you derive the debye-hückel theory? Without the derivation we cannot see what is the physical reasoning behind it...

[@PhysicalChemistry]

You've spotted one of the flaws in the course. I worked on some lectures deriving Debye-Hückel theory, but ended up not including them in the course, because the math needed is a little more involved than my students were prepared for, and the derivation is difficult to split naturally into 10-minute, single-lightboard segments. You're absolutely right that I haven't given you any physical insight into the equation. It's one of very few equations in the course where I give you the equation without telling you how to obtain it on your own, and it is like a thorn in my foot.

[@sahhaf1234]

@@PhysicalChemistry Ahah no worries.. The course is excellent as it is... If I had attempted to learn this from the books I'd spent months.. With your course, it have taken something like 10 days.. One question, though: A friend of mine wants to learn the chemical thermodynamics but she doesnt want to go through the statistical part. Which playlists she should watch, and in what order? (as I happen to know some thermo, I didn't watch the elementary parts and go through solutions, then electrolytes, and chemical equilibrium.. Hence I cannot advise her on that matter..)

[@sahhaf1234]

@@PhysicalChemistry I think the order goes like 1) Gases 2) thermodynamic state 3) spontaneity 4) free energy 5) Phase equilibria 6) Solutions 7) Electrolytic solutions 8) Chemical equilibrium..

[@PhysicalChemistry]

​@@sahhaf1234The full list, in order, is on the channel's "About" page. She can obviously skip anything she's not interested in. It's a bit ambiguous which parts are thermo and which are stat mech. For example, entropy is a very important thermo topic, but I treat it almost entirely with stat mech until we get to the free energy sections. I think the Boltzmann fundamentals are the best way to learn thermo, which is (of course) why I teach it that way. So skipping the stat mech sections will violate the course warranty. ;-) But any videos that rely on earlier topics (stat mech or otherwise) will have links to the earlier videos that introduced them.

[@sahhaf1234]

@@PhysicalChemistry Thanks a lot..🙂

[@martim664]

8:29 - shouln't Ion strenth be 0,025?

[@martim664]

Okay nevermind, i see now. It is Cl2 so it should be mulitply by 2 - my mistake

[@ishankavinda607]

good

[@PhysicalChemistry]

Thanks

[@PhongNguyen-fj6xz]

ln or log??? My teacher said :" LOG"

[@PhysicalChemistry]

Either one is okay, as long as you're careful to use the appropriate value for A (because ln x = 2.303 log₁₀ x). See the discussion @3:06

[@RohitKumar-ps3fe]

♥️♥️

[@aroobarahat7706]

Plz speak slowly slowly as my English is weak😊 So that I can understand clearly .. U r a good teacher but plz speak slowly slowly means say everything clearly😞😞😞

[@PhysicalChemistry]

If you click on the gear icon at the bottom of the videos, you can change the playback speed and make me talk as slowly as you like. Also, you can turn on subtitles, if that helps.

[@aroobarahat7706]

@@PhysicalChemistry ok ok thanks