Examples percent yield

Example 1 Yield from a Crystallization Process A 10,000-lh batch of a 32,5 percent MgS04 solution at 120°F is cooled without appreciable evaporation to 70°F, What weight of MgS04-7H20 crystals will be formed (if it is assumed that the mother liquor leaving is saturated) ... 

When we calculate a percent yield, the amounts can be expressed in either moles or mass, provided both the actual and theoretical amounts are in the same units. Example shows how to use Equation. ... 

According to Example, it is possible to make 443 g of geranyl formate from 375 g of geraniol. A chemist making geranyl formate for the preparation of a perfume uses 375 g of starting material and collects 417 g of purified product. What is the percent yield of this synthesis ... 

C04-0010. If the reaction described in Example produces 195 kg of HCN from 175 kg of methane reactant, what is the percent yield ... 

If the percent yield of a reaction is already known, we can calculate how much of a product to expect from a synthesis that uses a known amount of starting material. For example, the Haber synthesis of ammonia stops when 13% of the starting materials have formed products. Knowing this, how much ammonia could an industrial producer expect to make from 2.0 metric tons of molecular hydrogen First, calculate the theoretical yield ... 

A reaction that is carried out under limiting reactant conditions nevertheless has a yield that generally will be less than 100%. The reasons why reactions yield less than the theoretical amounts, given in Section 4-1. apply to all reactions. When a reaction operates under limiting reactant conditions, we calculate the theoretical yield assuming that the limiting reactant will be completely consumed. We then determine the percent yield as described in Section 4A. Example shows how to do this. 

The final amount in this table represents the theoretical yield. To determine the percent yield, we need to have actual and theoretical amounts in the same units. In this example, we work with moles ... 

The percent yield calculated in this way corresponds to the amount of product X relative to all products and is not the same as the percent of the starting material converted to X (this latter expression is given by x/a/Co, where C0 is the number of moles of reactant). It should be noted that similar to the relationship between rate and efficiency, a low quantum yield for a photochemical reaction does not necessarily mean that it will be formed in a low yield (the converse is true, however). If, for example, x = 0.005 and 2, t = 0.00005, then... 

The value of an intensive response is not a function of the size or throughput of the system. Product purity is an example of an intensive response. If a manufacturing facility can consistently produce 95% pure material, then it will be 95% pure, whether we look at a pound or a ton of the material. Other examples of intensive responses might be color, density, percent yield, alcohol content, and flavor. 

Many of you have already described procedures in a lab report. Most likely, you included items such as the equation that you used to calculate percent yield or the step-by-step instructions that you followed to complete a synthesis (e.g., Heat to reflux. or Stir constantly for 10 min. ). Are such items also appropriate in a journal article To answer this question, we analyze several different excerpts. Each excerpt describes a common chemical procedure. Although by no means comprehensive, these few examples should get you started and help you understand what an expert audience expects in this move of the Methods section. 

Acetoacetic ester synthesis is the preparation of substituted acetones, and it s an important method for creating a variety of products. It begins with the reaction of acetoacetic ester (a dicarbonyl) or a similar compound with a strong base to produce a carbanion, which then reacts with alkyl halide, RX. The structure of acetoacetic ester is in Figure 15-10. Figure 15-11 illustrates an example of an acetoacetic ester synthesis and two possible outcomes. Figure 15-12 shows the preparation of 2-heptanone with a 65 percent yield via the acetoacetic ester synthesis. Figure 15-13 presents the preparation of 2-benzylcyclohexanone with a 77 percent yield. 

In a multistep synthesis, the overall percent yield is the product of the fractional yields in each step times 100 and decreases rapidly with the number of steps. For this reason, a low-yield step along the way can mean practical failure for the overall sequence. Usually, the best sequence will be the one with the fewest steps. Exceptions arise when the desired product is obtained as a component of a mixture that is difficult to separate. For example, one could prepare 2-chloro-2-methylbutane in one step by direct chlorination of 2-methyl-butane (Section 4-5A). But because the desired product is very difficult to separate from the other, isomeric monochlorinated products, it is desirable to use a longer sequence that may give a lower yield but avoids the separation problem. Similar separation problems would be encountered in a synthesis that gives a mixture of stereoisomers when only one isomer is desired. Again, the optimal synthesis may involve a longer sequence that would be stereospecific for the desired isomer. 

A number of cases have been found in which 1,2-hydride shifts occur with retention at CB. For example, (> ) -6- (ami nomethyl) -2-methyloctane (32) is deaminated in aqueous perchloric acid to give 2,6-dimethyloctan-6-ol in 35 percent yield. This product is formed with 41 percent retention at CB. No fully satisfactory explanation for the retention has been proposed.44... 

The amount of product actually formed in a reaction divided by the amount theoretically possible and multiplied by 100% is called the reaction s percent yield. For example, if a given reaction could provide 6.9 g of a product according to its stoichiometry, but actually provides only 4.7 g, then its percent yield is 4.7/6.9 X 100% = 68%. 

Worked Examples 3.8 and 3.9 show how to calculate and use percent yield. 

Many industrial reactions are not carried to equilibrium. In this circumstance the reactor design is based primarily on reaction rate. However, the choice of operating conditions may still be determined by equilibrium considerations as already illustrated with respect to the oxidation of sulfur dioxide. In addition, the equilibrium conversion of a reaction provides a goal by which to measure improvements in the process. Similarly, it may determine whether or not an experimental investigation of a new process is worthwhile. For example, if the thermodynamic analysis indicates that a yield of only 20 percent is possible at equilibrium and a 50 percent yield is necessary for the process to be economically attractive, there is no purpose to an experimental study. On the other hand, if the equilibrium yield is 80 percent, an experimental program to determine the reaction rate for various conditions of operation (catalyst, temperature, pressure, etc.) may be warranted. 

From the previous example, what is the percent yield if only 8.2 g of ammonia is produced ... 

Development of a 200 kg/hr pyrolysis plant The pyrolysis process includes the biomass feeding section, the pyrolysis reactor and the liquid collection system. Various tests are discussed, demonstrating the technical feasibility of the process. For example, the yields of bio-oil, char and gas are typically 70, 15 and 15 weight percent. Finally, an economic evaluation of the pyrolysis process is presented in terms of the investment and bio-oil production costs. 

LAB that in order to compete, manufacturers must reduce the cost of making their products to the lowest level possible. Percent yield is important in the calculation of overall cost effectiveness in industrial processes. For example, sulfuric acid (H2SO4) is made using mined sulfur. Figure 12-8. Sulfuric acid is an important chemical because it is a raw material for products such as fertilizers, detergents, pigments, and textiles. The cost of sulfuric acid affects the cost of many of the consumer items you use every day. 

Since cyano groups may be hydrolyzed to carboxylic acids (Section 20.19), the Sandmeyer preparation of aryl nitriles is a key step in the conversion of arylamines to substituted benzoic acids. In the example just cited, the o-methylbenzonitrile that was formed was subsequently subjected to acid-catalyzed hydrolysis and gave o-methylbenzoic acid in 80-89 percent yield. 

In Examples 10.2 and 10.3, we determined the maximum amount of product that could be formed from the given amounts of reactants. This is the amount of product that could be obtained if 100% of the limiting reactant were converted to product and if this product could be isolated from the other components in the product mixture without any loss. This calculated maximum yield is called the theoretical yield. Often, somewhat less than 100% of the limiting reactant is converted to product, and somewhat less than the total amount of product is isolated from the mixture, so the actual yield of the reaction, the amount of product that one actually obtains, is less than the theoretical yield. The actual yield is sometimes called the experimental yield. The efficiency of a reaction can be evaluated by calculating the percent yield, the ratio of the actual yield to the theoretical yield expressed as a percentage. 

Example 10.4 shows how percent yield calculations can be combined with equation stoichiometry problems. 

Because the actual yield must be less than the theoretical yield, the percent yield is always less than 100%. In multistep reaction sequences, the percent yield of each step is expressed as a fraction and multiplied by the others to find the overall yield. The result may sometimes be surprising. For example, suppose a six-step reaction sequence has a 90.0% yield for each step, which is quite high. Even so, the overall percent yield would be... 

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