- 50.0=5.0 g-1078ChapterThreeStoichiometryCan we count these nonidentical beans by weighing? Yes. The key piece of informationwe need is theaveragemassof the jelly beans. Let's compute the average mass for our10-bean sample.total mass of beansAverage mass= -------number of beans5.1 g+5.2 g+5.0 g+4.8 g+4.9 g+5.0 g+5.0 g+5.1 g+4.9 g+5.0 g10Figure3.1.(left) A scientist injecting a sample into a mass spectrometer.(right) Schematic diagram of a mass spectrometer.The average mass of a jelly bean is 5.0 g. Thus, to count out 1000 beans, we need toweigh out 5000 g of beans. This sample of beans, in which the beans have an averagemass of 5.0 g, can be treated exactly like a sample where all of the beans are identical.Objects do not need to have identical masses to be counted by weighing. We simplyneed to know the average mass of the objects. For purposes of counting, the objectsbehaveas thoughthey were all identical,as though they each actually had the aver-age mass.
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