Conversion questions?

Question

1)How many atoms of copper are in a pure copper penny that weighs 2.15 g? (1 amu = 1.6605 10-24 g)

2)In nature, the element X consists of two naturally occurring isotopes. 107X with abundance 55.84% and isotopic mass 106.9051 amu and 109X with isotopic mass 108.9048 amu. Use the given information to calculate the atomic mass of the element X.

Avg mass = sum(abundance)(isotope mass)

Answer 1

2.15 g @ 1 mole Cu / 63.546 grams @ 6.022e23 atoms / mole =

your answer is: 2.04e22 atoms of copper

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X-107:

106.9051 amu (55.84%) = 59.69581

X-109:

108.9048 amu (44.16%) = 48.09236

59.69581 plus  48.09236 = 107.78817

your answer: 107.7882 amu