Constants Part A Atomic mass is a weighted average of the masses of the naturall

Question

Constants Part A Atomic mass is a weighted average of the masses of the naturally occurring isotopes of that element. For example, consider isotopes of lithium: On a mission to a newly discovered planet, an astronaut finds copper abundances of 69.15 % for 63Cu and 30.85 % for 65Cu. What is the atomic mass of copper for this location? The mass of 63 Cu is 62.9300 amu. The mass of 65 Cu is 64.9200 amu Express your answer to two decimal places, and include the appropriate units. Abundance Mass |(amu) isotope (%) 6.015 92.5 7.016 The atomic mass is therefore 6Li Li 7.5 View Available Hint(s) (0.075x 6.015) + (0.925 × 7.016) = 6.94 amu Notice that the atomic mass is closer to 7 than it is to 6. That is because the heavier isotope is more abundant. ValueUnits Submit

Explanation / Answer

atomic mass of Cu   = abundance * atomic mass of 63Cu + abundance * atomic mass of 65Cu

                                 = 0.6915*62.93   + 0.3085*64.92   = 63.54 amu

part-B

atomic mass of Si = abundance * atomic mass of 28Si + abundance * atomic mass of 29Si +abundance * atomic mass of 30Si

                             = 0.7371*27.98+ 0.1493*28.98+ 0.1136*29.97

                              = 28.35 amu

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