Answer
a) 0.25 mol of U b) 0.50 mol of Na c) 10 atoms of Fe
Work Step by Step
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.
