tailieunhanh - Modern Analytical Cheymistry - Chapter 9

Titrimetric Methods of Analysis Titrimetry, trong đó chúng ta đo khối lượng của một thuốc thử phản ứng stoichiometrically với các chất phân tích, lần đầu tiên xuất hiện như là một phương pháp phân tích trong những năm đầu thế kỷ thứ mười tám. Không giống như gravimetry, titrimetry ban đầu đã không nhận được chấp nhận rộng rãi như là một kỹ thuật phân tích. Nhiều người nổi tiếng cuối thế kỷ thứ mười chín nhà hóa học phân tích ưa thích gravimetry theo titrimetry và vài trong số các văn bản tiêu chuẩn từ thời kỳ bao. | Chapter 9 Titrimetric Methods of Analysis T itrimetry in which we measure the volume of a reagent reacting stoichiometrically with the analyte first appeared as an analytical method in the early eighteenth century. Unlike gravimetry titrimetry initially did not receive wide acceptance as an analytical technique. Many prominent late-nineteenth century analytical chemists preferred gravimetry over titrimetry and few of the standard texts from that era include titrimetric methods. By the early twentieth century however titrimetry began to replace gravimetry as the most commonly used analytical method. Interestingly precipitation gravimetry developed in the absence of a theory of precipitation. The relationship between the precipitateÕs mass and the mass of analyte called a gravimetric factor was determined experimentally by taking known masses of analyte an external standardization . Gravimetric factors could not be calculated using the precipitation reactions stoichiometry because chemical formulas and atomic weights were not yet available Unlike gravimetry the growth and acceptance of titrimetry required a deeper understanding of stoichiometry thermodynamics and chemical equilibria. By the early twentieth century the accuracy and precision of titrimetric methods were comparable to that of gravimetry establishing titrimetry as an accepted analytical technique. 273 274 Modern Analytical Chemistry titrimetry Any method in which volume is the signal. titrant The reagent added to a solution containing the analyte and whose volume is the signal. equivalence point The point in a titration where stoichiometrically equivalent amounts of analyte and titrant react. end point The point in a titration where we stop adding titrant. indicator A colored compound whose change in color signals the end point of a titration. titration error The determinate error in a titration due to the difference between the end point and the equivalence point. ĨA Overview of Titrimetry Titrimetric