Using Percents

The other reason for not using percent completion is that it involves no commitment on the part of individuals responsible for the event to finish at any particular time. To report that you are X per cent complete on an event is a subjective evaluation of history, not a statement of future plans and intentions. Thus, we often experience the phenomenon of completion percentages that increase by ever-smaller amounts and never quite reach 100 per cent. 

Doing conversions Mole-mole, mole-particles, mole-volume, and mole-mass Figuring out what happens when one reagent runs out before the others Using percent yield to determine the efficiency of reactions... 

Chemists don t have it so easy. Someone is paying them to do reactions. That someone doesn t have time or money for excuses about loitering reactants. So you, as a fresh-faced chemist, have to be concerned with just how completely your reactants react to form products. To compare the amount of product obtained from a reaction with the amount that should have been obtained, chemists use percent yield. You determine percent yield with the following formula ... 

If spiking method is used Percent recovery according to USP/ICH guidelines (depending on analyte concentration level)... 

For multiplication and division, use percent relative uncertainty. Absolute uncertainty can be found at the end of the calculation... 

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

Because numerical values for a CCV (ICV) percent drift and percent difference of a linear calibration are almost the same, laboratories often use percent drift as the acceptance criteria for linear calibrations. 

We can also use percent concentrations as conversion factors. For example, how many liters of D5W is required to deliver 100 g of glucose Well, D5W is 5% w/v) glucose, so we can interpret 5% as 5 g of glucose/100 mL D5W solution. That s a conversion factor, and now the units can take us to the answer. 

We can now use percents to handle everyday situations, such as leaving a tip or finding simple interest. You ve seen how to work with fractions, decimals, and percents. In the next chapter, well put all three together, converting and comparing among them. 

These concentration units are typically used when the concentrations are extremely small and it is impractical to use percent or molarity. 

It may be more reasonable to consider the percent of the commodity suj ly that is heated instead of the percent of the crop that is treated. By doing so, we can account separately for the amount of domestically produced commodity that is treated, as well as the amount of commodity imported into the country that is treated. Using percent of the commodity supply that is heated should allow EU dietary exposure assessments to avoid the practice of assuming that 100% of a commodity is heated. If evidence indicates that the entire food supply in a particular area is heated, additional assessments may be conducted with that assumption. 

COMMODITY NESTI 100 PERCENT COMMODITY TREATED USING PERCENT COMMODITY TREATED... 

You can also do this problem by using percent composition (Sec. 7.5). 

Generally, two types of analysis are used to determine BOD in the laboratory one where dilution is necessary and one where dilution is not necessary. When the BOD of a sample is small, such as found in river waters, dilution is not necessary. Otherwise, the sample would have to be diluted. Table 2.1 sets the criteria for determining the dilution required. This table shows that there are two ways dilution can be made using percent mixture and direct pipetting into 300-mL BOD bottles. Normally, BOD analysis is done using 300-mL incubation bottles. 

The consensus values cannot automatically be accepted as recommended to certified values because their analytical validity usually requires a re-assessment in the light of additional analytical information such as concentration level, number of different analytical methods used, percent of outliers and other criteria. In practice, certified or recommended values are always based on the following requirements data should be available from a certain number of participants and two or more different analytical methods there should be no significant differences between the groups of accepted results outliers should not exceed 20-30% of the submitted results. Depending on the extent to which the data satisfy such acceptance criteria, the consensus values are then assigned to one of the following conclusions certified or recommended concentration, information value, or not recommended. 

Use percent error to describe the accuracy of experimental data. 

Keep this figure in mind when doing problems using percent composition. You can always assume that you have a 100-g sample of the compound and use the percents of the elements as masses of the elements. 

Once the sun s irradiance and material s optical properties are integrated at each wavelength, the total of reflected solar energy may be summed resulting in a single number denoted as total percent solar reflectance for the air mass used. Percent solar absorptance is then calculated ... 

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