120 Chapter Three Stoichiometry 35. The element rhenium (Re) has two naturally occurring isotopes, 185Reand 187Re,with an average atomic mass of 186.207 amu. Rhenium is 62.60% 187Re, and the atomic mass of 187Re is 186.956 amu. Calculate the mass of 185Re. 36. Assume silicon has three major isotopes in nature as shown in the table below. Fill in the missing information. Isotope Mass (amu) Abundance 28Si 27.98 29Si 4.70% 32Si 29.97 3.09% 37. The element europium exists in nature as two isotopes: 151Euhas a mass of 150.9196 amu, and 153Euhas a mass of 152.9209 amu. The average atomic mass of europium is 151.96 amu. Calculate the relative abundance of the two europium isotopes. 38. The element silver (Ag) has two naturally occurring isotopes: 109Ag and 107Agwith a mass of 106.905 amu. Silver consists of 51.82% 107Agand has an average atomic mass of 107.868 amu. Calculate the mass of 109Ag. 39. The mass spectrum of bromine (Br2) consists ofthree peaks with the following characteristics: Mass (amu) Relative Size 157.84 159.84 161.84 0.2534 0.5000
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