Conductometry / conductometric titration
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This document provides an in-depth overview of conductometric titration, a technique used in analytical chemistry to measure the electrolytic conductivity of a solution during a titration process. It discusses the principles, advantages, and applications of conductometric titration, including its effectiveness in titrating colored solutions and those involving weak electrolytes. Key concepts such as conductivity, electrolytes, and the impact of ion size and temperature on conductance are also explained.
Conductometry / conductometric titration
- 2. Contents: 1. Introduction Conductance Electrolytes, Strong Electrolyte, Weak Electrolytes Specific Conductance Molar conductance Equivalent Conductance Dilution 2. Conductometric Titration 3. Conductometric titrationCurves Discussion 4. Advantages of Conductometric Titration 5. Application of Conductometric Titration 6. Conclusion
- 3. Abstract: Conductometric titration is a type of titration in which the electrolytic conductivity of the reaction mixture is continuously monitored as one reactant is added. The equivalence point is the point at which the conductivity undergoes a sudden change. Marked increases or decrease in conductance are associated with the changing concentrations of the two most highly conducting ions—the hydrogen and hydroxyl ions.The method can be used for titrating coloured solutions or homogeneous suspension (e.g.: wood pulp suspension), which cannot be used with normal indicators. The conductometric titration curve is a plot of the measured conductance or conductivity values as a function of the volume of the solution added. The titration curve can be used to graphically determine the equivalence point. 1. Introduction: Conductometry is a measurement of electrolytic conductivity to monitor a progress of chemical reaction. Conductometry has notable application in analytical chemistry, where conductometric titration is a standard technique. In usual analytical chemistry practice, the term conductometry is used as a synonym of conductometric titration, while the term conductimetry is used to describe non-titrative applications. Conductometry is often applied to determine the total conductance of a solution or to analyze the end point of titrations that include ions. Conductance:The powerof electrolytesto conductelectriccurrentsistermedconductivityor conductance. G = I/R Unit of Conductance: Siemens(S) The conductance of the solutionmainly depends on two factors: 1.Size of the ions: The conductivity of the solution is inversely proportional to the size of the ions .If the size of the ions is increasing then the conductivity of the solution will decrease because the mobility of the ions will decrease by increasing the size of the ions. 2. Temperature: By increasing the temperature, the mobility of the ions in the solution will increase. So temperature has a direct effect on conductance of solution. E.g. by increasing the temperature the conductance will increase and vice versa. Conductance Increases When: 1. Greater charge of ions 2. Smaller size of ions 3. Higher concentration of ions 4. Lower resistance of the solution
- 4. Electrolytes:are electrovalent substances that form ions in solution which conduct an electric current. Electrolysis: the phenomenon of decomposition of an electrolyte by passing electric current through its solution is termed electrolysis. Electrolytic Cell: contains water solution of an electrolyte in which two metallic rodes(electrodes) are dipped. Strong Electrolyte:Astrong electrolyteis a solute that completely, or almost completely, ionizes or dissociates in a solution. Strong acids, strong bases and mostly salts are strong electrolytes. They are good conductors of electricity and have a high conductanceeven at low concentration. Example:NaCl , HCl , HNO3, H2SO4, KCl , CuSO4 , ZnSO4 etc. Weak Electrolyte:A weak electrolyte is a substance which forms ions in an aqueous solution but does not dissociate completely. When dissolved, a weak electrolyte does not disperse completely into ions. The solution instead contains both ions and molecules. They have low value of equivalent conductance. Weak acids, weak bases and few salts are weak electrolytes. Examples: HF, HC2H3O2 (acetic acid), H2CO3 (carbonic acid), H3PO4 (phosphoric acid), Specific Conductance (K): It is defined as “The conductance of one centimeter cube(cc) of a solution of an electrolyte.” Specific Conductance Increases with: 1. Ionic concentration 2. Speed of the ions Units of Specific Conductance: ohm-1 cm-1, S cm-1 Molar conductance(u):it is defined as the conductance of all ions produced by one mole (one gram molecular weight) of an electrolyte when dissolved in a certain volume (cc). U= K*100/ M Equivalent Conductance (A): it is defined as the conductance of an electrolyte obtained by dissolving one gram equivalent of it in volume (cc) of water. A = K V
- 5. Dilution: The volume of water in which a certain amount of the electrolyte is dissolved is always measured in cubic centmeters (cc) and this is known as dilution. 2. Conductometric Titration:Conductometric titration is a type of titration in which the electrolytic conductivity of the reaction mixture is continuously monitored as one reactant is added. The equivalence point is the point at which the conductivity undergoes a sudden change. The principle of conductometric titration is based on the fact that during the titration, one of the ions is replaced by the other and invariably these two ions differ in the ionic conductivity with the result that conductivity of the solution varies during the course of titration. The equivalence point may be located graphically by plotting the change in conductance as a function of the volume of titrant added. In order to reduce the influence of errors in the conductometric titration to a minimum, the angle between the two branches of the titrationcurve should be as small as possible. If the angle is very obtuse, a small error in the conductance data can cause a large deviation. The following approximate rules will be found useful. •The smaller the conductivity of the ion which replaces the reacting ion, the more accurate will be the result. •The larger the conductivity of the anion of the reagent which reacts with the cation to be determined, or vice versa, the more acute is the angle of titration curve. •The titration of a slightly ionized salt does not give good results, since the conductivity increases continuously from the commencement. Hence, the salt present in the cell should be virtually completely dissociated; for a similar reason; the added reagent should also be as strong electrolyte. Conductometric Titration Curves are: 1.Strong Acid with a Strong Base, e.g. HCl with NaOH: Before NaOH is added, the conductance is high due to the presence of highly mobile hydrogen ions. When the base is added, the conductance falls due to the replacement of hydrogen ions by the added cation as H+ions react with OH− ions to form undissociated water. This decrease in the conductance continues till the equivalence point. At the equivalence point, the solution contains only NaCl. Afterthe equivalence point, the conductance increases due to the large conductivity of OH-ions.
- 6. 2. Weak Acid witha Strong Base,e.g. acetic acid with NaOH: Initially the conductance is low due to the feeble ionization of acetic acid. On the addition of base, there is decrease in conductance not only due to the replacement of H+ by Na+ but also suppresses the dissociation of acetic acid due to common ion acetate. But very soon, the conductance increases on adding NaOH as NaOH neutralizes the un-dissociated CH3COOH to CH3COONa which is the strong electrolyte. This increase in conductance continuesraise up to the equivalence point. The graph near the equivalence point is curved due the hydrolysis of salt CH3COONa. Beyond the equivalence point, conductance increases more rapidly with the addition of NaOH due to the highly conducting OH−. Conductometric titration of a weak acid (acetic acid) vs. a strong base (NaOH)
- 7. 3. Strong Acidwith a Weak Base, e.g. sulphuric acid with dilute ammonia: Initially the conductance is high and then it decreases due to the replacement of H+. But after the endpoint has been reached the graphbecomes almost horizontal, since the excess aqueous ammonia is notappreciably ionised in the presence of ammonium sulphate. 4. Weak Acid witha Weak Base: The nature of curve before the equivalence point is similar to the curve obtained by titratingweak acid against strong base. After the equivalence point, conductance virtually remains same as the weak base which is being added is feebly ionized and, therefore, is not much conducting. Conductometric titration of a weak acid (acetic acid) vs. a weak base (NH4OH)
- 8. Discussion: Upon dilution specific conductance decreases, while equivalent conductance and molar conductance increases. Increase in equivalent conductance in case of a weak electrolyte is due to increase in the number of ions. Advantages of Conductometric Titration: The main advantages to the conductometric titration are its applicability to very dilute, and coloured solutions and to system that involve relative incomplete reactions. Application of Conductometric Titration: It can be used for acid base, redox, precipitation, or complex titrations. Determination of sulphur dioxide in air pollution studies. Determination of soap in oil. Determination of accelerators in rubber. Determination of total soap in latex. Specific conductance of water. Conclusion: The electrical conductance of a solution is a measure of the solution’s ability to conduct electricity. The ability of a solution to conduct electric current decreases as the resistance of the solution increases. Electricity is conducted in a solution by ions of electrolytes. Conductance of electrolytes increases with the increase of temperature and concentration of electrolytes. The conductance of a solution is the sum of the conductance of all the ions in the solution. The conductance of an ion in solution is related to the charge, size and concentration of the ion. Conductometry can be used to locate the end point of the titration. Conductometric titration is useful for acid-base, precipitation, and complexation titrations. REFERENCE: 1. Introduction to Chemical Analysis, Robert D.Braun 2. Fundamental of Analytical Chemistry, Skoog,west. 3. Essentials of Physical Chemistry,Arun Bahl,B.S.Bahl,G.D.Tull 4. www.tau.ac.il/.../Files/conductometry-titrations.pdf 5. https://www.reference.com/.../definition-weak-electrolyte-3b8e99e7130207... 6. https://www.stolaf.edu/depts/chemistry/courses/.../elec.htm 7. www.citycollegiate.com/chapter3b.htm 8. https://en.wikipedia.org/wiki/Molar_conductivity