barium interference, Fe, gravimetry, iron

1. SHREE MALLIKARJUN COLLEGE SYBSC
SAFETY: Refer to MSDS of ferric chloride, ammonium chloride, ammonium hydroxide, sulphuric acid, hydrochloric acid
-Dr. Mithil S. Fal Desai
Aim: To estimate the amount of Fe as Fe2O3 in the given solution of ferric chloride containing barium
chloride and free HCl.
Chemicals: Ferric chloride, ammonium chloride, ammonium hydroxide, sulphuric acid, hydrochloric acid.
Apparatus: Beaker,funnel, Whatman 1 and 41, glass rod with policemen, waterbath, oven, silica crucible.
Theory: In the gravimetric estimation, iron is precipitated as Fe(III) hydroxide which is then sintered to
get Fe(III) oxide (Fe2O3). The ferric ions in the solution containing barium are separated by selective
precipitation of barium using sulfate ions.
Reactions:
Ba2+
(aq) + SO4
2-
(g)  BaSO4(s) ↓
Fe3+
(aq) + 3OH-
(aq)  Fe(OH)3(s) ↓
Procedure:
1) Pipette out 25 mL of the solution in a 250 mL beaker and add 1 mL of concentrated HNO3.
2) Heat the solution and add 20 mL of 2N H2SO4.
3) Digest the precipitate of BaSO4 and allow it to settle. (Check for complete precipitation)
4) Filter the solution through Whatman 1 and collect the Fe3+
ions in a 250 mL beaker, quantitatively.
5) Add 2 g of NH4Cland 30 mL of 6M NH4OH (red-orange precipitate is formed) and digest the precipitate
on water bath for 30 min.
6) After 30 min, cool the solution and add 5-10 mL of NH4OH solution along the sides of the beaker and
check for complete precipitation.
7) Collect the precipitate on a Whatman 41 filter paper and wash with distilled water until the filtrate is free
from Cl-
and SO4
2-
ions.
8) Carefully transfer the precipitate with the filter paper in a previously weighed silica crucible and heat it
on a low flame.
9) Once the paper is chared, ignite the precipitate to get Fe2O3.
10) Cool and weigh the crucible containing the precipitate.
(To get the constant weights, repeat the step 8 and 9)
11) The weight of precipitate quantitatively corresponds to the weight of Fe2O3.
Observation
Table 1.
The constant
weight of silica
crucible without
precipitate
“W1’ (g)
The constant
weight of silica
crucible with
precipitate
“W2’ (g)
Weight of
Fe2O3
‘A’=W2 – W1
(g)
Molecular weight
of Fe2O3
‘B’ (g)
Atomic weight of
Fe
‘C’(g)
Amount of Fe in
25 mL
‘x' = A*C*2/B
(g)
Result: Amount of iron in 500 mL is ______g.