Answer
a)
Aspirin: $1.80\times10^{-3}\ mol$
$NaHCO_3$: $4.315\times10^{-2}\ mol$
Citric acid: $5.205\times10^{-3}\ mol$
b) $1.08\times10^{21}\ molecules$
Work Step by Step
Atomic weights (g/mol): $C: 12.011,\ H: 1.008,\ O: 15.999,\ Na: 22.990$
Molar masses:
Aspirin ($C_9H_8O_4$): $9\times12.011+8\times1.008+4\times15.999=180.2\ g/mol$
$NaHCO_3$: $22.990+1.008+12.011+3\times15.999=84.01\ g/mol$
Citric acid ($C_6H_8O_7$): $6\times12.011+8\times1.008+7\times15.999=192.1\ g/mol$
a) Number of moles
Aspirin: $324\times10^{-3}\ g\div180.2\ g/mol=1.80\times10^{-3}\ mol$
$NaHCO_3$: $1904\times10^{-3}\ g\div84.01\ g/mol=4.315\times10^{-2}\ mol$
Citric acid: $1000\times10^{-3}\ g\div192.1\ g/mol = 5.205\times10^{-3}\ mol$
b) Number of molecules of aspirin:
$1.80\times10^{-3}\ mol\times6.022\times10^{23}\ molecules/mol=1.08\times10^{21}\ molecules$
