Learn everything about measurement of conductance in electrochemistry with this detailed Electrochemistry Lecture (4K). Understand the concept of conductance, specific and molar conductivity, experimental methods to measure conductance, and its applications in electrochemical analysis. Perfect for CSS aspirants, chemistry students, and anyone studying electrochemistry or physical chemistry. Watch the full lecture in 4K quality for clear visuals, step-by-step explanations, examples, and exam preparation tips.
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#Electrochemistry #MeasurementOfConductance #MolarConductivity #SpecificConductivity #CSSChemistry #PhysicalChemistry #ChemistryLecture #ChemistryEducation #ScienceLearning #ElectrochemistryTutorial #4K
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00:00Welcome everyone to this presentation on conductance and its measurement.
00:08In today's lecture, we are going to explore one of the most fundamental properties in electrochemistry, which is conductance.
00:18And we will understand how it plays a vital role in studying ionic movements in the solutions.
00:25We will begin by understanding what conductance is and how it differs from the resistance.
00:32After that, we will dive into how conductance is measured experimentally.
00:38We will learn about the Wheatstone bridge method, conductivity cells and the role of cell constant.
00:45We will also touch upon how temperature, concentration and nature of electrolytes affect the conductance.
00:54Let us begin with the basic definition of conductivity.
01:03In electrochemistry, conductivity refers to the ability of an electrolyte solution to conduct electric current.
01:11This property arises because electrolytes dissociate into ions in solutions.
01:18And these free ions are the charge carriers that enable the flow of electricity.
01:24So, formally, we defined conductivity or conductance as the ability of electrolytes to conduct electric current.
01:34Just like matter allow electrons to move and conduct electricity, in electrolytes, it is the ions that move and carry charges.
01:45An important thing to remember is that electrolytes behave similarly to metallic conductors when it comes to current flow.
01:55They obey OHAM laws.
01:58This means that the relationship between the current, the voltage and the resistance in an electrolyte is predictable and linear.
02:08Just like in metals.
02:13According to OHAM's law, the current, which is shown by I, flowing through a conductor is directly proportional to the potential difference across it.
02:25And it is inversely proportional to the resistance.
02:28Mathematically, this can be written as I is equal to E over R, where E is the potential difference across the two ends of the electrolyte, which is measured in volts, and R is the resistance of the electrolyte, which is measured in OHAM's.
02:51Now, let us look deeper into how the physical properties of a conductor influences its resistance, and how that resistance is connected to the conductivity.
03:04Resistance is a measure of how much material opposes the flow of electric current, and importantly, resistance is not just a fixed value.
03:14It changes depending on the certain physical dimensions of the conductor.
03:19First, resistance is directly proportional to the length of the conductor.
03:26That means, the longer the wire or the conductor, the more resistance it offers to the flow of electric current.
03:33This makes sense because electrons have to travel a greater distance, encountering more atomic illusions along the way.
03:42Secondly, resistance is inversely proportional to the cross-sectional area of the conductor.
03:49So, the wider the wire, the lower will be the resistance.
03:54A wider conductor allows more path for electrons to travel simultaneously, and it will reduce the overall opposition to the electric current.
04:04Putting these two values together, we get this basic relationship as R directly proportional to L over A.
04:12Or, if we remove this proportionality constant, we get the equation R is equal to Rho over L.
04:19Now, this Rho is a constant of proportionality and it is called resistivity or specific resistance.
04:27Its value depends upon the material of the conductor.
04:31It is a basic and essential concept in both physics and electrochemistry because it explains why wire dimensions matter when designing circuits or measuring conductivity.
04:44Now, bringing into the conductivity, the conductivity of a substance is essentially the reciprocal of resistance.
04:54If a substance has high resistance, it has low conductivity and vice versa.
05:00So, when we say a substance is a good conductor like copper or strong electrolytes, we mean that its resistance is low and its conductivity is high.
05:12Now, we will look into the specific conductance.
05:21To define, we can define as the reciprocal of a specific conductance is termed as specific conductance or specific conductivity.
05:31The material or the solution whose conductivity is to be measured is placed in a cell which has dimensions as 1 cm of length, 1 cm of width and 1 cm of height.
05:48So, these are the standard dimensions.
05:50We put the electrolyte in this cell and measure its resistance.
05:57And the value of resistance, the reciprocal of the resistance will give us the value of specific conductivity.
06:05In this slide, we are introducing a key classification in electrochemistry, which is strong electrolyte versus weak electrolytes.
06:19This classification is based on how well a substance ionizes in water and thus, how effectively it can conduct electricity.
06:28Now, in this slide, we are going to explore the strong electrolytes.
06:34Strong electrolytes are substances that plays a vital role in electrochemistry due to their excellent ability to conduct electricity in the solution.
06:44Now, we will define the strong electrolytes.
06:49A strong electrolyte is a substance that, when dissolved in water, ionizes almost completely, producing a solution with a high concentration of ions.
07:01This means that it dissociates into its constituent ions nearly 100%, producing a large number of free-moving ions in the solution.
07:12These ions are the actual carriers of the electric current in electrolytic solutions, which is why strong electrolytes are excellent conductors of the electricity.
07:25Because of high concentration of ions, strong electrolytes exhibit high equivalent conductance, even when the solution is very diluted.
07:34This is important in practical applications like batteries, electrolytes, and medical solutions, where consistent conductivity is needed.
07:46Now, we will look into the examples of some strong electrolytes.
07:51Strong acids.
07:53These are the acids that ionizes completely in aqueous solutions.
07:58Some of the examples include hydrochloric acid, sulfuric acid, nitric acid, perchloric acid, hydrobromic acid, hydroiodic acid, and many more.
08:12These acids release a large number of H plus signs, making them very strong proton donors and excellent conductors of the electricity.
08:23Strong bases.
08:24These bases completely dissociates to give hydroxyl ions or OH- ions in the solutions.
08:32Some of the examples are sodium hydroxide, calcium hydroxide, potassium hydroxide, and magnesium hydroxide.
08:42Next one is the salt.
08:46Practically, most common salts are strong electrolytes because they fully dissociate into cations and anions in the water.
08:56For instance, sodium chloride and potassium chloride.
09:00These salts conduct current very well due to their complete ionization and are widely used in both laboratory and industrial settings.
09:12The defining feature of the strong electrolytes is complete ionization.
09:17This makes them different from weak electrolytes which only partially ionizes and therefore conduct electricity less efficiently.
09:31Now we will discuss the weak electrolytes.
09:36A weak electrolyte is a substance that when dissolved in water does not fully split into ions.
09:44Only a small fraction of the molecules actually ionizes while most of them stays in the original form.
09:51This results in the fewer free-moving ions in the solution compared to strong electrolytes.
09:58Because there are very less ions available to carry the electric current, the solution formed by the weak electrolytes has low electric conductivity.
10:12So, even if you dissolve a lot of the amount of weak electrolytes in the water, it still will not conduct electricity as well as strong electrolytes would.
10:29Now we will look into the examples of the weak electrolytes.
10:34A good example of the weak electrolytes are the weak acids, especially organic acids.
10:42Think of the acidic acid which is the main acid in the vanager.
10:47It only ionizes a little in the water.
10:50Others include the oxalic acid and the sulfurous acid which is the H2SO3.
10:57Both of these acids are also only partially ionized in the solution.
11:04Then we have the weak bases.
11:07Weak bases are the organic compounds like alkyl amines.
11:14One example is the ethyl amine, the formula with C2H5 and H2.
11:23These bases don't produce many hydroxide ions when dissolved in water.
11:29So, their solutions are very weak conductors of the electricity.
11:34There are also some salts that behave as weak electrolytes.
11:39For example, mercury 2-chloride and lead 2-acetate are the weak electrolytes.
11:46They don't fully dissociate into ions in the water which makes them poor conductors of the electricity.
11:53So, overall, weak electrolytes are substances that partially ionize and form less conductive solution.
12:02You will basically or usually encounter them in the form of certain acids, bases or salts.
12:10Especially those involving organic components or some of the heavy metals.
12:20Now, let us understand the relationship between conductance and the resistance.
12:27They are actually reciprocal of each other.
12:30That means, when one goes up, the other goes down.
12:34So, if we know the resistance of a solution, we can easily figure out its conductance by just taking the reciprocal of the resistance or the conductance.
12:46It is a very simple math but super useful in the electrochemistry.
12:50This gives us a practical way to measure conductance in the lab.
12:56Instead of trying to directly measure how well a solution conducts electricity, we measure how much it resists to the electric current.
13:05And then, we can calculate the conductance from that.
13:09A simple formula is given as G is equal to 1 over R, R is the resistance and G or C can be the conductors of the solution.
13:21One of the classic instruments used for this measurement is the Wheatstone bridge.
13:28It is a very clever circuit that let us measure an unknown resistance very precisely by balancing it against known resistance.
13:38So, in our case, we can connect the electrolytic solution into the bridge circuit and figure out its resistance.
13:47Once the resistance is measured, with the help of the Wheatstone bridge, we simply take its reciprocal to get the conductance and we can get the conductance of the solution.
13:59This technique provides us a reliable and very accurate way to study how well different electrolytes carry electric currents.
14:08Now, let us talk about how the actual setup for measuring conductance looks like.
14:20The core of the setup is what we call a conductance cell.
14:24This is the special container where we place the electrolytic solution whose conductance is to be measured.
14:31Inside the conductance cell, we have two platinum electrodes.
14:40These are not just any platinum wires.
14:42They are coated with platinum black, which is a rough, finely divided form of the platinum.
14:48This coating increases the surface area and ensures better and more consistent contact with the solution, which gives us more accurate readings.
14:58These platinum electrodes are attached to platinum wires and those wires are sealed inside two narrow glass tubes.
15:10This helps insulate and protect the electrical connections while keeping everything stable and secure.
15:19To complete the circuit, we use something a little old school, but very effective, which is the mercury contacts.
15:29These are pools of mercury placed inside the glass tube, which allows a smooth, low resistance electrical connections from the platinum wire to the rest of the measuring circuits.
15:44Here we can see the setup of the conductance cell.
15:48These are the two platinum electrodes, which are coated with the platinum black.
15:53Here is the electrolytic solution.
15:56Then we have the mercury contact, which is inside the tube.
16:00And we have the copper wires, which are made for the connections.
16:03One will be the positive wire and other one will be the negative wire.
16:08Let us now walk through the circuit arrangement used for measuring the resistance of the conductance cell.
16:19This setup is a classic example of Wheatstone bridge, which is modified fire for AC measurements.
16:27First, you can see the arrangement for the Wheatstone bridge, which is a circuit for measuring the resistance of the solution.
16:39First, we have AB, which is this one.
16:44We can see the AB wire, which is a manganin wire.
16:49Manganin is chosen because it has a very low temperature coefficient of resistance, meaning its resistance stays stable even if the temperature fluctuates.
17:00This wire is tightly stretched over a meter roll, allowing us to make precise measurements based on the sliding contact position.
17:10Then we have the sliding contact shown by the H.
17:15The sliding contact is like a movable probe.
17:18It can glide along the manganin wire and allows us to adjust the point of balance in the circuit.
17:25When the circuit is balanced, the motion at the position of H gives us the information we need to calculate the resistance.
17:34Then we have the box R, which is the resistance box.
17:40This is a standard lab instrument used to introduce non-resistance into the circuit.
17:47We use it here to calibrate the system and balance the bridge.
17:55Then we have the conductance cell, which is represented by the C.
18:00This is the part that contains our electrolytic solution.
18:05It is connected in the circuit, so we can measure its resistance by comparing it to the non-resistance from the resistance box.
18:13So, resistance R and the resistance of the electrolyte is measured and is balanced.
18:20Some of the values will be obtained, which can be used to calculate further parameters of the solution.
18:28For example, the resistance or the conductance.
18:31For the power source, we use the induction coil, which is labeled as I.
18:40This coil provides alternating current instead of direct current.
18:46Alternating current is used because it avoids problems like electrolysis or polarization of the electrodes in the cell,
18:54which can interfere with accurate resistance measurement in the solution.
18:59Finally, we use a headphone instead of traditional galvanometer.
19:05Headphone is shown by this sphere.
19:09When the bridge is balanced, there is no sound.
19:13If there is an imbalance, meaning the voltage difference, we will hear a tone.
19:20So, the headphone helps us detect change in the resistance very sensitively through this sound.
19:28So, basic function of the headphone is that if to balance the resistance of both this box R and this electrolytic solution C, which is shown by the sphere.
19:40If both of these resistances are balanced, then we will not hear any sound in this headphone.
19:47All of these components, which are shown here, work together to help us precisely measure the resistance of the solution, which we can then use to calculate the conductance.
20:06Now, let us talk about what actually happens during the measurement process using the wet weedstone setup.
20:16First, we remove or unplug any resistance from the resistance box R, which is shown here.
20:25This step ensures that only unknown resistance in the circuit is coming from the solution inside the conductance cell.
20:33So, this resistance or the conductance should be of the known value.
20:39Next, we slide the contact edge along the manganine wire.
20:44As we move it, we listen carefully through the headphones connected to the circuit.
20:50The goal here is to find the point where the sound in the headphone is at its minimum.
20:56The point means that the bridge is balanced.
21:00And when it is balanced, it tells us that potential difference on both sides is equal.
21:07First side is the, this side are these two points.
21:10These two points are for this conductance cell.
21:14And these two points are for the resistance.
21:17So, the resistance or the potential difference is balanced.
21:22So, when the sound is at its minimum, we note the value from the resistance box and the corresponding position of the sliding contact edge on the slide.
21:35This gives us the measured resistance of the electrolytic solution.
21:39But, if we are not done yet, we are really interested in the conductance of the solution.
21:48And more specifically, the specific conductance.
21:51Here we can see that the resistance or the simple formula.
21:58The resistance C of the electrolytic solution corresponds to the resistance of the BH, which is the length of this manganine wire.
22:08So, C corresponds to the resistance of BH.
22:13And the resistance R, the value of resistance R corresponds to the length of A to H, which is the length of the A to H.
22:23So, by measuring the length, we can measure the resistance.
22:27So, by this formula, the resistance of the conductance cell C can easily be calculated.
22:40The resistance in the solution can be converted into the specific conductance.
22:54To get the specific conductance, we use this simple formula.
22:59Specific conductance is equal to 1 over R multiplied by L over A.
23:05Here we can see that L over A corresponds to X, which is basically the cell constant.
23:11So, we convert the resistance to conductance by taking the reciprocal of R and then multiply it by the cell constant, which is represented by the X.
23:26And just like that, we can now quantitatively express how well our solutions conduct electricity.
23:34Now, we will understand the role of geometry in conductance measurements.
23:44In the equation of resistance, we have seen that resistance R is directly proportional to the length of the conductor and inversely proportional to the class sectional area A.
23:55So, if we combine these two geometric forces into a single ratio, it will be L over A.
24:04This ratio represents how the shape and size of the conductance cell affect resistance.
24:11For convenience, we give this ratio a new symbol X.
24:16And it is called cell constant.
24:20The cell constant X is unique to a given conductance cell.
24:25Meaning, once it is known, it does not change unless the cell itself is changed.
24:32It has units of per centimeter.
24:35So, after measuring the resistance of the solution, we can use the simple formula which was given in the previous slide to calculate the specific conductance.
24:45After determining the specific conductance, which is the K, we can now move further and calculate two very important types of conductance.
25:00Which is the equivalent conductance and the other one is the molar conductance.
25:05Equivalent conductance tells us how well one gram equivalent of an electrolyte conduct electricity in a solution.
25:13And the molar conductance, it gives us the conductance of one mole of electrolyte, making it a great way to compare the conductance power of different substances.
25:26The expression used for the equivalent conductance is given below as A is equal to specific conductance multiplied by 1000 over N.
25:37Here, K is the molar conductance and it is multiplied by the volume of the solution in a one molar of solution.
25:47Here, N is the gram equivalent of the electrolyte.
25:54These values are extremely helpful when comparing strong and the weak electrolyte.
26:01Also, the formula is given for the molar conductance.
26:05And using these two formulas, we can calculate equivalent conductance and the molar conductance from the specific conductance.
26:14Here, M is the gram mole of the electrolyte and N is the gram equivalent of the electrolyte.
26:22Now, let us talk about how we actually determine the cell constant, which as we just discussed, is the ratio of length L between the electrodes to the cross sectional area A.
26:45In theory, we could just measure these physical dimensions directly, measure the distance between electrodes and the area of their surfaces and then divide L by A.
26:57But in practical lab settings, this is not so easy.
27:01These electrodes are small and the measurements are very delicate and not always accurate using mechanical tools.
27:09Because of these challenges, scientists and the engineers and chemists don't typically measure the dimensions directly.
27:18Instead, we use an indirect method.
27:32Moving on to the determination of cell constant.
27:36Now that we know that what the cell constant is, let us see how we can actually calculate in the lab using a standard solution of KCl or the potassium chloride.
27:47So, we use a standard solution whose specific conductance is already known with high accuracy, such as potassium chloride solution at a known concentration and temperature.
27:59So, we place this standard solution, we place this standard solution in the conductance cell, measure the resistance or using the circuit setup and then apply these formulas.
28:09We know that the cell constant is equal to K multiplied by R.
28:14L over A is the cell constant.
28:17So, if we just rearrange this equation by moving R from here to here.
28:24So, K multiplied by R is equal to cell constant.
28:28Okay.
28:29Since K is already known or the specific conductance is already known from the reference data and R is measured, we can easily calculate the cell constant.
28:38Once the cell constant is known for that conductance cell, we can use it later for any other solution in the same cell to calculate the unknown specific conductance.
28:49Because cell constant does not change, so measuring a cell constant with a single solution will help us to experiment further with other solutions.
29:00So, basically to determine the cell constant, we use a standard solution of KCL whose specific conductance at a given temperature is already known.
29:10Then a solution of KCL of the same strength is prepared and its conductance determined experimentally at the same temperature.
29:19This method is very simple, practical and highly accurate and it is how most laboratory conductance measurements are standardized.
29:29So, thank you very much.
29:35I hope you have learnt something new and let me know of any feedback in the comment box.
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