Chapter 2 - Sections 2.1-2.9 - Exercises - Problems by Topic - Page 82: 84a

Mass of sample = $0.28005 g$

Molar mass of Sb = $121.76 g/mol$ Amount of sample = $2.3\times 10^{-3} mol $ Hence, mass of sample = molar mass $\times$ amount in mol = $$121.76 g/mol\times 2.3\times 10^{-3} mol = 280.05 \times 10^{-3} g = 0.28005 g$$