tailieunhanh - Modern Analytical Cheymistry - Chapter 8

Gravimetric Methods of Analysis Gravimetry bao gồm tất cả các kỹ thuật mà chúng tôi đo lường khối lượng hoặc thay đổi một khối lượng. Khi bạn bước trên một quy mô sau khi thực hiện bạn đang làm, trong một nghĩa nào đó, xác định trọng lực khối lượng của bạn. Đo khối lượng cơ bản nhất của tất cả các phép đo phân tích, và gravimetry nghi ngờ gì nữa là các kỹ thuật phân tích lâu đời nhất. . | Chapter 8 Gravimetric Methods of Analysis G ravimetry encompasses all techniques in which we measure mass or a change in mass. When you step on a scale after exercising you are making in a sense a gravimetric determination of your mass. Measuring mass is the most fundamental of all analytical measurements and gravimetry is unquestionably the oldest analytical technique. 232 Chapter 8 Gravimetric Methods of Analysis 233 8A Overview of Gravimetry Before we look more closely at specific gravimetric methods and their applications let s take a moment to develop a broad survey of gravimetry. Later as you read through the sections of this chapter discussing different gravimetric methods this survey will help you focus on their similarities. It is usually easier to understand a new method of analysis when you can see its relationship to other similar methods. Using Mass as a Signal At the beginning of this chapter we indicated that in gravimetry we measure mass or a change in mass. This suggests that there are at least two ways to use mass as an analytical signal. We can of course measure an analyte s mass directly by placing it on a balance and recording its mass. For example suppose you are to determine the total suspended solids in water released from a sewage-treatment facility. Suspended solids are just that solid matter that has yet to settle out of its solution matrix. The analysis is easy. You collect a sample and pass it through a preweighed filter that retains the suspended solids. After drying to remove any residual moisture you weigh the filter. The difference between the filter s original mass and final mass gives the mass of suspended solids. We call this a direct analysis because the analyte itself is the object being weighed. What if the analyte is an aqueous ion such as Pb2 In this case we cannot isolate the analyte by filtration because the Pb2 is dissolved in the solution s matrix. We can still measure the analyte s mass however by chemically .