Question

Escaping from the haunted house, Anna ran home immediately to her chemistry lab
back at the high school. After analysis of the gold heart, she found the heart was not
composed of pure gold, but gold (III) oxide (Au203). What percentage (by mass) was
gold in the heart?
a) 10.9% Au
C) 89.1% Au
b) 81.2% Au
d) 92.9% Au

Answer 1

89.1% Au

The molar mass of Au2O3 is 2(196.97) + 3(16.00) = 441.94 g/mol
The mass percent of Au is therefore 2(196.97) / 441.94, which is 393.94/441.94 = 0.891 —> 89.1%