In 1961, scientists agreed that the atomic mass unit (amu)would be defined as the mass of an atom of 12C. Before then,it was defined as the average mass of an atom of naturally occurring oxygen (a mixture of 16O, 17O, and 18O). The current atomic mass of oxygen is 15.9994 amu. (a) Did Avogadro’snumber change after the definition of an amu changed and, if so,in what direction? (b) Did the definition of the mole change?(c) Did the mass of a mole of a substance change? (d) Before1961, was Avogadro’s number 6.021023(when considered tothree significant figures), as it is today?

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Q: (a) What is the mass, in grams, of 4.62  1023 molecules of aspirin, C9H8O4?

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Mole Concept

Mole concept is a method to determine the amount of any substance that consists of some elemental particles using a grouping unit called ‘mole’. The mole concept enables one to handle the large amount of small elementary particles. The mole concept can be used in many calculations related to mole calculation, molar amount, mole ratio, and so on, which are significant in chemistry.