How many milliliters of carbon dioxide gas at stp are produced from the decomposition of 4.55 g of ferric carbonate?
fe2(co3)3(s)→fe2o3(s)+3co2(g)

Okey Dokie, so this is all occurring at STP. Therefore, 1 mol of a substance would equal 22.4 L. So what we are going to do is find the moles of the ferric carbonate and convert that to carbon dioxide, then convert to L and convert that to mL. You ready?
Ferric carbonate's molar mass is 2(55.85)+3(12.01)+9(16.00) = 291.73 g/mol
Find the mol.
4.55 g / 291.73 g = .0155966133 mol of ferric carbonate.
Convert to carbon dioxide gas. For every one mol of ferric carbonate, you get 3 mol of carbon dioxide.
0155966133 mol ferric carbonate * 3 mol carbon dioxide/1 mol of ferric carbonate.
.0467898399 mol of carbon dioxide * 22.4 L carbon dioxide/1 mol carbon dioxide
1.048 L carbon dioxide * 1000 mL/1 L 
If I am correct, there should be about 1050 mL of carbon dioxide, 3 significant figures. I hope this helps :-)

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