a. Determine the number of grams in 0.750 moles of the compound Iron
(II) phosphate: Fe3(PO4)2
b.How many atoms of iron are in 0.750 moles of the compound Iron(III)
oxide?

Hello teatea,

a. In order to find the mass for 0.750 moles, we must first find the
molar mass of the entire compound, and then multiply this value by
0.75.  The molar mass can be found by adding the molar masses of the
elements of the compound using values (in grams) that are found on any
periodic table.  This means that we added the molar mass of Fe 3
times, P 2 times, and O 8 times, which summed to 357.489.  Multiplying
this value by 0.75, we find that the total number of grams is 268.12.

b. First we have to find the empirical formula of the compound by
balancing the charges of the ions. Fe is +3, and O is -2. In order to
balance the compound, there must be 2 Fe and 3 O atoms per molecule.
Since there are .75 moles of compound, there must be 2 times that many
Fe atoms, making 1.5 moles. A mole contains 6.02 x 10^23 atoms, thus
the total number of Fe atoms is 9.03 x 10^23.

Please feel free to request a clarification if any part of the answer
is unclear, before you rate it.

Thanks,
chis-ga