## Chemistry and Chemical Reactivity (9th Edition)

The ratio of their atomic weights is $1.94$ The atomic weight of phosphorus is $31.0\ g/mol$:
Initial mass of P: 0.744 g Final mass of $P_4O_{10}$: 1.704 g Mass of O: 1.704-0.744 = 0.960 g Given their proportions (4:10): P: $0.744/4=0.186\ g$ O: $0.960/10=0.096\ g$ The ratio of their atomic weights is then $0.186/0.096=1.94$ Assuming the atomic weight of oxygen is 16.000 g/mol, the atomic weight of phosphorus is $1.94\times16=31.0\ g/mol$: