## Chemistry and Chemical Reactivity (9th Edition)

Atomic weights (g/mol): $Na: 22.990,\ Si: 28.085,\ U: 238.03,\ Fe: 55.845,\ K: 39.098$ a) Na: $0.5\ mol \times 22.990 g/mol = 11.5\ g$ Si: $0.5\ mol \times 28.085 g/mol = 14.0\ g$ U: $0.25\ mol \times 238.03 g/mol = 59.5\ g$ 0.25 mol of U represents more mass b) $0.50\ mol\times22.990\ g/mol=11.5\ g$ $1.2\times10^{22} atoms \div (6.022\times10^{23}\ atoms/mol)\times22.990\ g/mol = 0.46\ g$ 0.5 mol of Na represents more mass. c) Fe has a bigger atomic weight than potassium, so in the same number of atoms, Fe represents more mass.