00:00Hello everyone. Welcome to this exciting lecture series on electrochemistry.
00:07In this video, we are going to talk about an important concept in electrochemistry, which is a liquid junction potential.
00:17This phenomenon comes into play when solutions of different ionic concentrations come into contact with each other.
00:25It is a subtle yet significant factor that can influence the accuracy of the chemical measurements.
00:32So, when two electrolytic solutions of different concentrations come into contact, a liquid junction potential will develop.
00:42This occurs because the more concentrated solution naturally tends to diffuse into the less concentrated one due to the concentration gradient.
00:53Here, visually, we can see that at one side, there is 0.01 molar N-OH solution and on the other side, we have 0.001 molar N-OH solution.
01:06So, at the center, a liquid junction potential will develop.
01:11And we will see how this junction potential is developed.
01:17Okay.
01:18The rate of diffusion of each ion.
01:21We can see here, there are two ions or there can be more than two ions in some of the solutions.
01:26The rate of diffusion of each ion is not the same.
01:30It is roughly proportional to the ion's speed in an electric field.
01:34This means that different ions move at different speed, creating an imbalance during the diffusion.
01:41If an ion's diffusion more rapidly than the cations, they move further into the dilute solution, which will create a charge separation.
01:51The result is that the dilute solution becomes negatively charged, while the concentrated solution becomes positively charged.
01:59Here, we can see that if OH- ions move from here to here, the more concentrated solution will become positively charged, while the less concentrated solution will become negatively charged.
02:16Okay.
02:17So, as ions with different diffusion speeds move across the junction, an electrical double layer is formed.
02:23This there consists of positive and negative charges that accumulate at the interface between the two solutions.
02:30Okay.
02:31This unequal movement of ions create a potential difference at the point where the two solutions meet.
02:39The resulting potential is known as the liquid junction potential.
02:42Okay.
02:43Or, it can also be known as a diffusion potential.
02:46It arises due to ion transfer and it represents a non-equilibrium potential.
02:52It does not follow equilibrium thermodynamic models because the system is still in the motions.
03:00The magnitude of this potential is not fixed.
03:03Rather, it depends on the relative speed of the different ions in the solution.
03:08The greater the disparity in ion mobility, for example, if one ion moves significantly faster than the other, the larger potential will be created at the center of the two solutions.
03:21So, here we can look into the diagram and see what it means.
03:26We can have two solutions with different concentrations.
03:31If there is more, here on the left side, we have more concentrated solution.
03:37And on the right side, we have less concentrated solutions.
03:41From the more concentrated solutions, the negative ions move faster than the NOH ions.
03:48If they are moving faster than the Na plus ions, they diffuse into the less concentrated solution.
03:55As negative ions move from here to here, so we can see that this side will have more negative charge or more number of negative ions in the solution.
04:04So, negative ions will accumulate on the right side and the positive ions will accumulate on the left side.
04:11Due to this difference, we can see a wall between these two solutions.
04:16This wall will create a potential difference.
04:19And this potential, as it is happening in the liquid, we can call it simply a liquid junction potential.
04:27So, this is basically a potential difference between positive and negative ions, which happens or created between the two solutions.
04:40This was all about the liquid junction potentials.
