What is the mass in grams of 3.25 mol fe2(so4)3?

The answer is 1296.75 g

Molar mass of Fe2(SO4)3 is the sum of atomic masses of its elements:
Mr(Fe2(SO4)3) = 2Ar(Fe) + 3Ar(S) + 12Ar(O)
Ar(Fe) = 55.84 g/mol
Ar(S) = 32.06 g/mol
Ar(O) = 16 g/mol

Mr(Fe2(SO4)3) = 2 * 55.84 + 3 * 32.06 + 12 * 16
                         = 111.68 + 96.18 + 192
                         = 399.9 g/mol

Thus there are 399.9 g in 1 mol and x grams in 3.25 mol:
399 g : 1 mol = x : 3.25 mol
x = 399 g * 3.25 mol : 1 mol
x = 1296.75 g

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