The chemical formula "Ba"_3"P"_2"Ba3P2 indicates that in one mole of barium phosphide, there are three moles of barium ions, "Ba"^(2+)"Ba2+.
In order to determine the number of moles of barium ions in "4.960 g Ba"_3"P"_2"4.960 g Ba3P2, use the molar mass of barium phosphide and the given mass. The molar mass of barium phosphide is "473.928 g/mol"473.928 g/mol.
4.960cancel"g Ba"_3"P"_2xx(1"mol Ba"_3"P"_2)/(473.928cancel"mol Ba"_3"P"_2)="0.010466 mol Ba"_3"P"_2"
To determine the number of moles of barium ions in "0.010466 mol Ba"_3"P"_2", multiply the moles of barium phosphide times the moles of barium ions in one mole of barium phosphide.
0.010466cancel"mol Ba"_3"P"_2xx(3"mol Ba"^(2+))/(1cancel"mol Ba"_3"P"_2)="0.03134 mol Ba"^(2+)"
In order to determine the mass in grams of barium ions, multiply the molar mass of barium times the moles of barium ions.
0.03134cancel"mol Ba"^(2+)xx(132.327"g Ba")/(1cancel"mol Ba"^(2+))="41.47 g Ba"^(2+)
The mass of electrons are so negligible that the loss of them to form barium ions makes the molar mass of barium essentially the same as the molar mass of barium ions.
