Question

In the gravimetric analysis of iron, hydroxide may be added to a solution containing Fe2+ to

precipitate a gelatinous mess which is ignited to form Fe2O3. If 0.2864 grams of Fe2O3 were formed

from the ignition process, how many grams of FeCO3 were contained in the original sample that

was analyzed?

Answer 1

1) FeCO₃+2NaOH=Fe(OH)₂+Na₂CO₃

2) 4Fe(OH)₂+O₂=2Fe₂O₃+4H₂O

M(Fe₂O₃)=159.6900 g/mol

n (Fe₂O₃)=m/M=0.2864/159.6900=0.0018 mol

In the second reaction: n (Fe(OH)₂)=2 x n (Fe₂O₃)=0.0018 x 2 = 0.0036 mol

In the first reaction: n (FeCO₃) = n (Fe(OH)₂) = 0.0036 mol

M (FeCO₃) = 115.8540 g/mol

m (FeCO₃) = M x n = 115.8540 x 0.0036 = 0.4156 g