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Principles of Volumetric (Titrimetric) Analysis

Clinical Analytical Chemistry CLS 231. Principles of Volumetric (Titrimetric) Analysis. Lecture 5 Lecturer: Amal Abu- Mostafa. Principles of Volumetric (Titrimetric) Analysis. Volumetric analysis in one of the most useful analytical techniques. It is fairly rapid and accurate .

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Principles of Volumetric (Titrimetric) Analysis

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  1. Clinical Analytical Chemistry CLS 231 Principles of Volumetric (Titrimetric) Analysis Lecture 5 Lecturer: Amal Abu-Mostafa

  2. Principles of Volumetric (Titrimetric) Analysis • Volumetric analysis in one of the most useful analytical techniques. It is fairly rapid and accurate. • The word titration is used to express a volumetric type analysis. There are different types of titrations.

  3. General principles of titrations: • Practical setup on the bench

  4. General principles of titrations: • In a titration, the test substance (analyte of unknown concentration) is reacted with a reagent of exact known concentration (titrant, standard solution). • This reagent is also known as a primary standard reagent and is prepared in the lab. This reagent is usually added from the burette whereas the analyte is placed in a conical flask.

  5. General principles of titrations: • The titrant is added onto the analyte in a drop wise fashion accompanied by good mixing. Enough titrant is added until all the analyte reacts with an equivalent amount of the titrant. When that is achieved the tap of the burette is closed and the volume of titrant used is recorded. (End Point). • Since the exact concentration of the titrant is known and its volume used to reach the end point of the reaction is known, the concentration of the analyte can be calculated.

  6. Requirements of a titration: • The stoichiometry (ratio of reaction) and the chemical nature of the reaction between titrant (standard solution) & analyte should be known and well defined. Eg:- HCL + NaOH→NaC L + H2O Ratio of Reaction 1 : 1 1 H2SO4 + 2NaOH→ Na2SO4 + 2H2O Ratio of Reaction 1 : 2 1 • The above examples are those of an acid – base type titration.

  7. Requirements of a titration: • The reaction between titrant & analyte should be rapid. This helps to achieve results quickly. • There should be no side reactions between the titrant and molecules other than analyte that could react with the titrant in a similar manner. This means that there should be no side reactions & the reaction should be specific.

  8. Requirements of a titration: • There should be a marked change in some physical property of the solution when the reaction is complete and reaches the end point. In the titration between acids & bases there is a marked increase in the pH of the reaction mixture when the reaction is complete. A color change is usually brought about by addition of 2 drops of an indicator phenolphthalein whose color is dependent up on the acidity of the solution.

  9. Requirements of a titration: • The end point at which an equivalent amount of titrant is added is called the EQUIVALENCE POINT. The point at which the reaction is observed to be complete is called the END POINT.

  10. Properties of a titrant: • It should be 100 ± 0.02% pure. • It should be stable in solution especially at room temperature. • It should be readily available & cheep. • It is preferred to be of relatively high molecular weight. This provides higher accuracy when weighing.

  11. Types of Titrations: Depending on the type of reaction between titrant and analyte, there are different types of titrations:- • Acid – base titrations • Precipitation titrations • Complex metric titrations • Redox titrations The names reflect the nature of the chemical reaction between titrant & analyte

  12. Volumetric (Titration) Calculations: • Principles: • For any titration calculation a starting equation must be written to indicate equivalent amounts of analyte and titrant at the end point of the titration reaction. • Thus at the end point : • Amount of titrant(standard solution) = Amount of analyte • The molarity of titrant or analyte can be calculated depending on the data available in the question. • ( M x V) = (M\ x V \) n titrant n \ analyte

  13. Volumetric (Titration) Calculations: • A 25.0 ml sample of HCl solution is placed in a flask with a few drops of phenolphthalein (indicator). • If 32.6 ml of 0.185 M NaOH is needed to reach the end point, What is the concentration (M) of the HCl solution? • NaOH(aq) + HCl(aq)→NaCl (aq) + H2O (L)

  14. Solution: • V \ HCl = 25 mL • VNaOH = 32.6 mL • MNaOH = 0.185 M • ( M x V) = (M\ x V \) n titrant n \ analyte • ( M x V) = (M\ x V \) n NaOH n \ HCl • ( 0.185 x 32.6) = (M\ x 25) 1 NaOH 1HCl • M\HCl = 0.241 mol / L

  15. Thank you

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