Purity percentage yield

You can apply your knowledge of stoichiometry and percentage yield to solve problems related to percentage purity. 

In this section, you have learned how the amount of products formed by experiment relates to the theoretical yield predicted by stoichiometry. You have learned about many factors that affect actual yield, including the nature of the reaction, experimental design and execution, and the purity of the reactants. Usually, when you are performing an experiment in a laboratory, you want to maximize your percentage yield. To do this, you need to be careful not to contaminate your reactants or lose any products. Either might affect your actual yield. 

C. Some 1 -propanol of uncertain purity is used in the reaction. If 116 g of Na2Cr207 are consumed in the reaction and 28.1 g of propanoic acid are produced, what is the percentage yield ... 

The first question is addressed by working out the percentage yield, and Table 3.1 gives an idea of the expectations here. Section 4 addresses the problems of checking purity and Section 5 considers identifying the new compound. Determining the structure of a compound is a very complex process, and we devote all of Part 2 of this book, which is to be found on the Spectroscopy CD-ROM, to answering this question. 

Usually reaction engineering concentrates on maximizing the yield and minimizing the residence time in a reactor. For enantioselective catalysis processes, maximizing the (enantiomeric) purity if even more important. The chemical purity of a chiral compound is defined as the percentage in the product. A high chemical purity is not... 

The reasons for these choices are as follows. For most practical purposes a compound of a reasonably high degree of enantiomeric purity is the desired goal of an enantiosclcctivc reaction. The most convenient way to achieve this result is by recrystallization of the product or a derivative. This process, in the majority of cases, involves separation of the pure enantiomer from the racemate. The ee value, being equivalent to the percentage of the major isomer in the mixture with the racemic compound, defines the maximum yield of the pure isomer that can... 

Because ee and op values are not suited for mathematical formulae, it is much simpler and clearer if enantiomer ratios are used, Up to around 1980 it was the custom, as assessed from older textbooks and reviews, to define enantiomeric and optical purity by fractions and use terms enantiomeric and optical yield for the percentage values as described earlier. 

Since 5-Amino-tetrazole (ATZ) was not available commercially at that time, Benson (Ref 3) also reported a method for the synthesis of ATZ of 99% purity in 70-85% yield by reaction of Na nitrate aminoguanidine bicarbonate dissolved in nitric acid, followed by treatment with Na acetate. Davis (Ref 4) prepd Cal. 50 gun proplnts and determined the optimum percentage of 5 to 10% ATZ without DNEB (Dinitroethylbenzene), but coated with 5 to 0.8% DNT, gave acceptable service ballistics. 

A 5.135 g sample of impure limestone (CaC03) yields 2.050 g of C02 (which was absorbed in a soda-lime tube) when treated with an excess of acid. Assuming that limestone is the only component that would yield C02, calculate the percentage purity of the limestone sample. 

With beet juice, attention is paid especially to the percentage of sugar and to the quotient of punty. For a fixed sugar content, juices with the higher quotients of purity give greater yields of the final product. Invert sugar s found in but very small quantity and Only in altered juice. 

Finally, when working in the field of asymmetric synthesis, the organic chemist needs to quote both the chemical yield and the optical yield. The percentage optical yield or optical purity [enantiomeric excess (ee) %], is calculated thus ... 

The directions for the preparation differ from those for the preparation of sodium paraperiodate only in that 135 g. of potassium chlorate is used and 195 g. of pure potassium hydroxide. Since the latter always contains water, its percentage purity must be known. The yield is nearly 180 g. (98 to 99 per cent), and the purity is 99.5 per cent. 

Determine the percentage purity of a reactant based on the actual yield of a reaction. 

Thickness and, correspondingly, capacitance variation was less than 2%. The absence of impurity peaks in XPS spectra of silica-coated specimens clearly demonstrates the achieved purity. Yield, defined as the percentage of functioning vs. total measured capacitors, was 100%. Breakdown field strength was in the range 1.1-5.4 MV/cm and leakage current was about lO -lO A/cm at 0.5 MV/cm. Capacitance density was 23-350 nF/cm dependent on thin film thickness and materials. No breakdown was observed after 20 cycles between 0-40 V. Time dependent dielectric breakdown (TDDB) was 185 s at 40 V for ten of the patterned capacitors. 

Problem 14.5 Suppose that, under SnI conditions, 2-bromooclane of specific rotation -21,6° was found to yield 2-octanol of specific rotation +4.12°. Usmg the rotations for optically pure samples given on p. 462, calculate (a) the optical purity of reactant and of product (b) the percentage of racemization and of inversion accompanying the reaction (c) the percentage of front-side and of back-side attack on the carbonium ion. 

Once loading studies have been performed, scale-up can take place. First, the amount of feed material needed to yield the desired quantity of impurity must be determined. An FIPLC assay or other chemical assay can be used to determine the potency of the feed with respect to the desired impurity. If an assay is not available, the impurity potency can be approximated from analytical peak collection. Additionally, an estimation of the recovery yield (percentage of impurity present in feed that is recovered from the separation) can be obtained from a mass balance on the high-loading peak collection experiments. Off-cuts, fractions collected from the column that contain the impurity but do not meet purity, can often be recycled into the feed for the next run, increasing the recovery yield. The required preparative column volume can then be calculated as follows ... 

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