Learn everything about conductometric titrations in this detailed Electrochemistry Lecture. Understand the principle of conductometry, how to perform titrations based on conductivity changes, interpretation of titration curves, and applications in analytical chemistry and electrochemical analysis. Perfect for CSS aspirants, chemistry students, and anyone studying electrochemistry or analytical chemistry. Watch the full lecture for step-by-step explanations, examples, and exam preparation tips.
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#Electrochemistry #ConductometricTitrations #ElectrochemicalAnalysis #CSSChemistry #PhysicalChemistry #ChemistryLecture #ChemistryEducation #ScienceLearning #AnalyticalChemistry #ChemistryTutorial
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00:00Hello everyone. Welcome to this exciting lecture series on electrochemistry. In this video,
00:10we will learn about conductrometric titrations, which is a fascinating and a practical application
00:16of electrochemistry. In traditional titrations, we rely on indicators to signal the end point,
00:24but what if the solution is colored or the reaction does not suit visual indicators?
00:31That is where conductometric titrations come in. This method uses electrical conductivity to detect
00:38the end point of a chemical reaction, making it highly accurate and suitable even for difficult
00:44systems. In today's lecture, we will understand how this technique works, what type of reactions
00:51it's best suited for, and how conductivity changes during the titration process.
00:57We will also look at the graphical methods used to determine the end point and discuss
01:02some real world application in acid-base precipitation and redox titrations. So,
01:09let us get started and explore how we can use conductivity to make titrations more precise and
01:16powerful. Let us now talk about conductometric titrations. These are a special type of titration
01:26where instead of using indicators to find the end point, we measure the electrical conductance of the
01:32solutions during the reaction. And we can define it as the titrations in which conductance measurements
01:39are made use of in determining the end point of an acid-alkly reactions, some displacement reactions,
01:46or precipitous reactions, and these are called the conductometric titrations. This method is especially
01:54useful for acid-alkly reactions, some displacement reactions, and even precipitous reactions.
02:02By tracking how the conductance changes as we add the titrant, we can accurately determine the point
02:11at which the reaction is complete. So, what does the conductance actually depend on? There are basically
02:21two key factors. First one is that the number of ions present in the solution. More ions mean better
02:29ability to conduct electricity. Second one is that the mobility of these ions. This refers to how
02:37quickly the ions can move through the solution under an electric field. Faster ions contribute more to
02:44the conductance. As the titration progresses and the ionic composition of the solution changes,
02:50the conductance also changes. And we can use that trend to identify the end point
02:58without needing any color change indicators.
03:07Now, let us take a closer look at the principle behind the conductometric titrations.
03:13During any titration, what is essentially happening is that one type of ion in the solution is being
03:20replaced by the other ion. Now, since different ions have different abilities to carry electric current,
03:27this replacement causes a change in the overall conductivity of the solution. For example,
03:33if a fast-moving electron is replaced by a slower one, the overall conductivity of the solution will decrease,
03:39and vice versa. So, the difference in the ionic conductivities of the reacting ions
03:45play a key role in how the solution's conductivity changes over time.
03:49It is also important to note that cations and anions have different conductance values.
03:58So, which ions are involved which will influence the conductivity pattern during the titration?
04:06Another important point is that a chemical reaction must occur for these conductivity changes to be
04:11meaningful. Without an actual reaction between the titrant and the analyte, there would be no significant
04:18shift in the conductivity. Now, moving on to the theory. It tells us that we can detect the endpoint of titration
04:28simply by monitoring the changes in the solution's conductivity. By endpoint, we mean that the reaction is complete.
04:36So, instead of relying on a color change, we watch how the conductance changes and use that to
04:43find the exact point at which the titration ends, or in other words, the reaction is complete.
04:54Let us walk through an example of neutralization reaction in the context of conductometric titrations.
05:01In the beginning,
05:05as we start adding the base to the acidic solution, the H plus signs from the acid starts getting neutralized.
05:12They are replaced by the cations of the base, which usually have lower mobility, compared to H plus signs.
05:19Since H plus signs are highly mobile and contribute significantly to the conductivity, replacing them
05:26with the slow-moving cations causes the conductivity to decrease during this initial stage.
05:34Then we reach the equivalence point, where all the H plus signs have been neutralized.
05:40Now, as we continue to add more base beyond this point, we are just increasing the number of ions in the
05:47solution, particularly from the excessive base. This leads to arise in the concentration of free ions
05:54again, which starts increasing the overall conductivity of the solution again.
05:59So, if we plot the conductance on a graph against the volume of base added, we will see two
06:08separate lines with opposite slopes. One slope downward before the equivalence point and the other slope
06:16upward after the equivalence point.
06:17The point with these two lines intersect is the equivalence point and that is how we can determine the
06:29endpoint of the neutralization reaction through conductometric method.
06:35Let us go over an example to make this clearer. A strong acid versus strong base titration using HCl and
06:48sodium hydroxide. In this setup, hydrochloric acid which is a strong acid is placed in the conductivity vessel
06:56Initially, the solution has H plus and Cl minus signs. Since hydrogen ions are highly mobile,
07:11they contribute significantly to the solution's conductivity. As we begin adding NOH, a neutralization
07:18reaction reaction takes place. H plus ions react with OH minus ions from the NOH to form water and are thus
07:26replaced by the NA plus ions. Now, because sodium ions are slow moving ions than the hydrogen ions,
07:34the overall conductance begins to drop. This is the decreasing part of the graph.
07:41The reaction happening here is given below. Here we can see that in the reactant side,
07:46we have some of the ions. From these ions, H plus ions and hydroxyl ions are being combined to form the
07:52water and sodium ions and chloride ions are in the dissociated form. Once we have added just enough
08:00NOH to neutralize all of the H plus ions, that is the equivalence point, any additional NOH increases the
08:08number of free ions, which is the NOH plus ions and OH minus ions, which causes the
08:16conductance to rise again. So, the graph will clearly show the intersection of these two lines
08:23and that is how we can detect the end point accurately without any visual indicator. The first
08:31line is the decreasing line where H plus ions are being replaced by the sodium ions and second one is
08:37the line after the equivalence point where with the further addition of NOH, conductance starts to rise.
08:46We will also look at that in the next slide.
08:53So, the question is what happens after the equivalence point in a conductometric titration
09:00between a strong acid like HCl and a strong base like NOH. Up to the equivalence point, each drop of NOH added
09:10is used to neutralize H plus ions, which form water and reducing the number of highly mobile H plus
09:18ions in the solution. As a result, the conductance decreases steadily. But once we have added just enough
09:26NOH to neutralize all of the H plus ions, any further addition of the sodium hydroxide means
09:33that we are now simply adding excessive OH minus ions to the solution.
09:39Here is the key point. OH minus ions are the fast-moving ions and almost as mobile as H plus ions. So, adding
09:50more of them increases the conductivity or conductance of the solution significantly.
09:58This marks a turning point from a decreasing trend to an increasing trend. So, after the equivalence point,
10:06the conductance starts to rise with the addition of each drop of NOH.
10:14On a conductance versus volume graph, this behavior gives us two straight lines with opposite slopes.
10:23One going down before the equivalence point and the other going up after the equivalence point.
10:30The point where these two lines intersect, labeled as point B, is the end point of the titration.
10:36And that is what we look for to determine when the reaction is complete.
10:47Now, let us look at a different scenario. A titration between a weak acid and a strong acid,
10:54like acetic acid and gastric sodium hydroxide.
10:58In this case, since acetic acid is a weak acid, it does not ionize completely in the water. That means,
11:08the initial conductance of the solution is quite low, because there are very few free ions available
11:14to carry current. As we begin to add NOH, it reacts with the weak acid to form sodium acetate,
11:23which is a highly ionized salt. So, as the reaction proceeds, the number of ions in the solution
11:29starts to increase slowly. This results in the gradual and steady increase in the conductance
11:38as we approach the equivalence point, unlike the sharp drop we saw earlier in the strong acids.
11:44At the equivalence point, all the acetic acid have been neutralized. Beyond this point,
11:53any extra NOH added introduces free hydroxyl ion into the solution. And since, as we have studied
12:01earlier, the OH- ions are fast-moving ions, the conductance now starts to increase sharply.
12:08Here we can see the simple reaction. Here is the acetic acid ions, which is the CH3COO- ion,
12:16and H-plus ion, and sodium hydroxide ion, which is the Na+, and OH- ions. Again, like the previous slide,
12:27here H-plus ion starts combining with the OH- ion forming H2O, and the only end main are these two ions.
12:38So, again, when we plot conductance versus volume of base added, we will see a gradual upward slope
12:46before the equivalence point. This is a gradual upward slope. It is not a decreasing slope,
12:52but a gradual increasing slope. But the slope is not very high because there are very few ions
12:59given by the weak acid, which is the acetic acid. It will be followed by a much steeper slope after the
13:10equivalence point, which is shown by the point B. This makes it easy to identify the end point on the graph.
13:15So, simply, we can also measure the conductance or the end point of the weak acids or the strong
13:26by reacting it with the strong base graphically. Okay. So, this is a very simple method.
13:33Next, let us now consider the titration of a strong acid with a weak base. For example,
13:46hydrochloric acid is titrated against ammonium hydroxide. At the start, HCl is fully ionized,
13:56providing HCl and chloride ions, with HCl being very fast-moving ions, and it contributes greatly
14:07to the solution's conductance. As we start adding ammonium hydroxide, which is a very weak base and only
14:15partially ionized in the water, it reacts with the HCl to form water and NH4 plus ions.
14:22So, here is the equation that HCl, NH4 plus ions and OH minus ions. Again, H plus ions are being
14:33combined with the OH minus ions to form water. So, we remain with the two ions. Positive ion is the
14:40ammonium ion and the negative ion is the chloride ion. So, what happens to the conductance? It starts
14:50to decrease because we are replacing fast-moving H plus ions with slow-moving NH4 ions, which reduces the
14:59solution's ability to conduct electricity. Okay. Now, here is the interesting part.
15:08After the equivalence point, when all of the H plus ions have been neutralized,
15:12adding more NH4OH or the ammonium hydroxide does not significantly change the conductance.
15:21That is because NH4OH is itself a very weakly ionized and it does not contribute many extra ions to the
15:29solution. As a result, the conductance levels of and remains almost constant beyond the equivalence
15:38point. Because there are no much ions to transport the electricity or the current between the electrodes.
15:48On a conductance
15:51versus volume graph, we will see a decline in the conductance leading to the equivalence point
15:57B and then a flattening out beyond the equivalence point or after the completion of the reaction or after
16:09when all of the H plus ions are being neutralized in the reaction. So, this is a simple graph between
16:15strong acid and a weak base.
16:18Finally, let us discuss the titration between a weak acid and a weak base. For example, acetic acid
16:29titrated against the ammonium hydroxide. At the start, both the acid and the base are only partially ionized,
16:37so initial conductance is relatively very low. As the titration proceeds, acetic acid reacts with
16:44ammonium hydroxide to form ammonium acetate, which is a strong electrolyte.
16:52Because ammonium acetate dissociates completely into wines, the conductance of the solution increases
16:57as more salt is being formed. This increase in conductance continues steadily right up to the
17:07equivalent point. The reaction involved is given below. Here we can see the sum of the ions in the left
17:16side. H plus ions are combined with the OH minus ions to form the water and here we have seen positive
17:24and negative ions. Both of these ions are slow moving ions. Now, here is the graph. We can see that there is a
17:35gradual increase in the conductance of the cell after every addition of the weak base or weak acid.
17:45Okay, so beyond the equivalence point, which is the point B, adding more weak base does not change the
17:53conductance significantly because both reactants and the products are weakly ionized or the salt is already
17:59formed. So, on the graph, you will see a gradual increase in the conductance up to the
18:05end point, followed by a straight line beyond it, showing a very little little change. This pattern
18:13allows us to determine the end point of the titration by identifying where the conductance levels off.
18:19Okay, so simply by observing the leveling of the conductance, we can measure the end point of the
18:24titration. Now, let us explore a different kind of titration, a precipitation titration such as silver
18:35nitrate titrated against potassium chloride. In this titration, the reaction forms a precipitate
18:42specifically sealed silver chloride, which is an insoluble solid that settles out of the solution.
18:49The reaction is given as AgNO3 plus KCl. They both react to form KNO3 plus AgCl. This AgCl is basically a
18:58solid precipitate. Both silver ions and K plus ions have almost same mobilities. It means that they move
19:08through the solution at roughly the same rate. Because of this, the conductance of the solution remains
19:14almost constant throughout the addition of the titration or titrant up to the equivalence point.
19:20There is not much increase or decrease in the conductance of the solution.
19:26The reason is that both of these ions have similar conductivities. However,
19:31when all of the Ag plus ions or the silver A plus ions have precipitated out, i.e., at the equivalence
19:41point, any further addition of KCl adds excessive chloride ions and K plus ions to the solution.
19:49This causes a sharp increase in the conductance beyond the equivalence point, as it is evident from
19:55this graph. On the conductance versus the volume graph, this shows as a flat or
20:01nearly flat graph until the equivalence point before the end point. It is followed by a rapid increase
20:08of the conductance after that. This clear change helps us accurately identify the end point of the
20:15precipitation reactions. Now, let us talk about some of the key advantages of the conductometric
20:26titrations, which make them very useful in the various analytical situations. First, only a small
20:33quantity of solution is needed to carry out the titration, which is very helpful when sample amounts
20:39are limited or expensive. Since the end point is determined graphically, by observing the changes in
20:46the conductance, we don't need to worry about factors like color change or subjective observation.
20:54No special visual precautions are necessary also. Another major benefit is that no chemical
21:01indicators are required. This makes conductometric titrations ideal for analyzing colored or turbid
21:08solutions where color indicators would be hard to see or unreliable. Conductometric titrations are also
21:18very effective for analyzing dilute solutions or weak acids and bases where traditional titration methods
21:28may struggle with accuracy. Moreover, this method is quite versatile and it can be applied not only to
21:37acid or base titration but also to the mixtures of acid precipitation reactions and other complex
21:45titrations. Lastly, because conductors' measurements rely on direct electrical properties, they tend to give
21:54more precise and accurate results compared to some classical titration techniques. All of these
22:01advantages explain why conductometric titrations are widely used in both research and industrial laboratories.
22:09While conductometric titrations offer many advantages, it is important to also be aware of some of its
22:22limitations. First, if the solution has a high concentration of salt, it can interfere with the measurement and result in the
22:31that inaccurate conductance readings. This is because the extrins contribute to the conductness and mask the changes caused by the titration reactions.
22:43Similarly, the presence of other electrolytes besides the species being analyzed can also affect the accuracy.
22:52These additional lines add to the total conductivity and can distort the titration curve,
23:00which make it harder to pinpoint the end point correctly.
23:06Another limitation is that conductometric titrations have limited use in the redox titrations.
23:13This is because the redox reactions don't always involve significant changes in the ionic mobility or the concentration.
23:21So, the conductance may not vary enough to detect the end point reliably.
23:27So, while conductometric titration is powerful, it is important to consider these factors when choosing the right method for your analysis.
23:36Let us now look at some important applications of conductometric titrations that highlight their practical usefulness.
23:48One key application is in monitoring pollution in the water.
23:52Conductometric titrations help detect the presence and concentration of various ionic pollutants
24:00by measuring changes in their conductivity.
24:02They are also used to determine the basicity of organic acid,
24:06which is important in the fields like pharmaceuticals and chemical manufacturing.
24:12Another application is measuring the deuterium mine concentration in the water,
24:21which is a specialized analysis useful in the certain scientific and industrial processes.
24:27Conductometric titrations method helps to determine the solubility of sparingly soluble salts,
24:40giving insight into the behavior of salt that dissolves only slightly in the water.
24:47These titrations are widely used for the quantitative analysis of various compounds,
24:52providing precise measurements of ions and their concentrations.
24:59In environmental chemistry, conductometric titrations are used to assess the alkalinity of water,
25:06which indicates the water capacity to neutralize acid.
25:10Finally, they are also applied to measure the salinity of water,
25:15water, which is important in the water quality control and marine studies.
25:22Overall, the versatility and accuracy of the conductometric titrations make them very
25:28valuable tools across environmental, industrial and the research fields.
25:33So, that is the end of our lecture. I hope you have learned something new.
25:46Okay, thank you.
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