00:00Hello everyone. Welcome to this exciting lecture series on electrochemistry.
00:07In this video, we are going to dive into an important concept in electrochemistry, which is activity and activity coefficient.
00:20First of all, let us clarify what we mean by the activity.
00:25In simple terms, activity refers to the effective concentration of anion or electrolyte in a solution.
00:32It shows not just how much of the substance is present but how much is actually active or participating in the chemical processes.
00:43It is symbolized by a small a and it gives us more accurate picture than the concentration alone, especially when dealing with real and non-ideal solutions.
00:54Mathematically, activity can be defined using this simple equation.
01:01A will be equal to C multiplied by F.
01:04Here in this equation, C stands for the molar concentration of the solution.
01:09That is what we normally measure in the mole per liter or we can say the molarity.
01:15And F is the activity coefficient which adjusts the concentration to reflect how ions interact in the solution.
01:25We have seen that in an ideal solution where everything behaves perfectly and there is no ion interaction, F is basically equal to 1.
01:35That means the activity just equal to the concentration and A will be equal to C because F has become 1.
01:45But as we move on to the more realistic or concentrated solutions, ions start interacting more.
01:52They repel or retract each other which affect how free they are to participate in the action.
01:58That is when F becomes less than 1 and activity drops below the actual concentration.
02:05So, in some of the realistic solutions, activity coefficient can be less than 1.
02:13We can rearrange the equations like this to define the activity coefficient.
02:19Activity coefficient will be equal to the activity divided by the concentration of the solution.
02:26We can see that the parameter F tells us how much the real solution deviates from the ideal behavior.
02:37If F will be equal to 1, it is ideal.
02:41If F will be less than 1, there is some interference between the ions.
02:47To define the activity coefficient, we can define F the ratio of activity to the actual concentration of the solution.
02:56This concept is extremely useful in advanced electrochemistry, especially when calculating things like the cell potentials,
03:03equilibrium constants, or interpreting results from the titrations.
03:08This concept is also very important when we deal with real-world solutions that are not ideally diluted,
03:18like some in industrial or biological systems where the effective behavior of ions can be very different from what their concentration suggests.
03:28Next, we will see that how we define the activity of an electrolyte.
03:37The activity of electrolyte is defined as the product of the activities of cations and anions.
03:43Rather than considering just a single ion, the activity of the entire electrolyte takes into account both the cations and the anions that make up the compound.
03:55So, activity of the electrolyte if the pressure is entered by the symbol A and it is calculated as the product of the activities of the two ionic components,
04:06which is the positive ion and the negative ion.
04:09Here, A plus is the activity of the positive ion called cation and A negative is the activity of negative ion called cation.
04:18This gives us a more accurate picture of the real behavior of the electrolyte in the solution, especially when we are not dealing with the ideal conditions.
04:27In the same way, we can determine the activity coefficient of the electrolyte.
04:36This, too, is the product of the activity coefficient of both of the ions.
04:42Here, we can see that the activity coefficient or the overall activity coefficient is equal to activity coefficient of cation multiplied by activity coefficient of anions.
04:55In this equation, F plus is the activity coefficient of cation and F minus is the activity coefficient of the anion.
05:06These coefficients, both of these coefficients, reflect how much the behavior of the ions deviate from the reality,
05:13especially in concentrated solutions where interionic interactions are stronger.
05:18For dilute solutions, both F plus and F minus are close to one, which means that the ions act almost ideally.
05:27But as the concentration increases, these coefficients usually drop, indicating the non-ideal behavior in the solution.
05:34So, but the individual activity and the activity coefficient of an ion in an electrolyte cannot be measured directly through experiments.
05:50This is because we cannot isolate a single ion to measure its behavior independently.
05:56In this equation, ions are always existing pairs or groups to maintain the electrical neutrality in the solution.
06:07But we can measure their mean value of the activity and the activity coefficient.
06:13To measure the main activity of the electrolyte, for example, Ax and By, which can be any compound,
06:19these values can be measured by this equation.
06:22Here is the psychometric equation, Ax, By, ionizes into A plus signs and B minus signs.
06:29Here, x and y are the coefficients and y plus and B minus are the charges on these components.
06:38So, here is a simple equation.
06:40To measure the or calculate the activity of the positive and negative winds,
06:45we can use this equation, which is v under root A plus x dot A minus y.
06:51Here, in this equation, v represents the total number of ions present in the solution,
06:56which can be simply obtained by summing up the x and y.
07:02So, that is all for today's lecture.
07:08Thank you very much.
07:11Please leave your seat.
07:12Thank you very much.
07:13Thanks again next week.
07:15See you next week.
07:17Bye-bye.
07:25Bye-bye.
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