22-02-2013, 02:24 PM
DETERMINATION OF COPPER IN BRASS
Theory :
In an analysis of brass a known weight of clean and dry turnings
are heated with hot conc. HNO3. Tin gets precipitated as
metastannic acid and can be removed by filtration. The filtrate
containing soluble salts of copper, zinc, lead, and iron is treated
with conc.H2SO4 and evaporated to dryness. The dry mass
comprising of PbSO4 is treated with distilled water and filtered.
The clear filtrate containing CuSO4 (blue), ZnSO4 (colorless) and
FeSO4 (light green) is taken for estimation of copper in Brass. A
known aliquot filtrate is treated with excess of KI in neutral of
feebly acidic medium which reduces Cu2+ to Cu+ and liberates an
equivalent amount of I2.Thus, the librated I2 during reaction is
estimated by titration with a standard Na2S2O3 solution using
starch indicator. The amount of copper in the filtrate is found out
and hence the percentage of copper in the brass can be
calculated. This is an Iodometric titration which deals with
liberated I2 during the reaction
Procedure :
Preparation of the solution of Brass sample:
1. Weigh accurately 1.0 gm of brass alloy turnings and treat with
about 30 ml of conc. HNO3 on a porcelain dish.
2. Heat the solution to around 100°C for 10 – 15 minutes, when
tin separates out as a white precipitate of metastannic acid
(H2SnO3).
3. Cool and filter the solution. Wash the precipitate with hot
water and estimate the amount of Sn.
4. The filtrate and washings are taken in another porcelain dish
and treat with about 50 ml of conc. H2SO4.
5. The solution is evaporated to dryness.
6. The dry mass is extracted with about 100 ml distilled water
when Pb, if any appears as a white precipitate.
7. Filter and wash the residue with cold water and estimate Pb.
The filtrate and washings containing CuSO4, ZnSO4 and
FeSO4 (in traces) is taken in a 250 ml volumetric flask.
Result : The given sample of brass contains = ________ % of Copper.
Theory :
In an analysis of brass a known weight of clean and dry turnings
are heated with hot conc. HNO3. Tin gets precipitated as
metastannic acid and can be removed by filtration. The filtrate
containing soluble salts of copper, zinc, lead, and iron is treated
with conc.H2SO4 and evaporated to dryness. The dry mass
comprising of PbSO4 is treated with distilled water and filtered.
The clear filtrate containing CuSO4 (blue), ZnSO4 (colorless) and
FeSO4 (light green) is taken for estimation of copper in Brass. A
known aliquot filtrate is treated with excess of KI in neutral of
feebly acidic medium which reduces Cu2+ to Cu+ and liberates an
equivalent amount of I2.Thus, the librated I2 during reaction is
estimated by titration with a standard Na2S2O3 solution using
starch indicator. The amount of copper in the filtrate is found out
and hence the percentage of copper in the brass can be
calculated. This is an Iodometric titration which deals with
liberated I2 during the reaction
Procedure :
Preparation of the solution of Brass sample:
1. Weigh accurately 1.0 gm of brass alloy turnings and treat with
about 30 ml of conc. HNO3 on a porcelain dish.
2. Heat the solution to around 100°C for 10 – 15 minutes, when
tin separates out as a white precipitate of metastannic acid
(H2SnO3).
3. Cool and filter the solution. Wash the precipitate with hot
water and estimate the amount of Sn.
4. The filtrate and washings are taken in another porcelain dish
and treat with about 50 ml of conc. H2SO4.
5. The solution is evaporated to dryness.
6. The dry mass is extracted with about 100 ml distilled water
when Pb, if any appears as a white precipitate.
7. Filter and wash the residue with cold water and estimate Pb.
The filtrate and washings containing CuSO4, ZnSO4 and
FeSO4 (in traces) is taken in a 250 ml volumetric flask.
Result : The given sample of brass contains = ________ % of Copper.