|
|
|
| |
| |
Analytical
method for Copper
|
| |
DETERMINATION OF COPPER CONTENT AND PURITY IN COPPER(ll) SULPHATE
PENTAHYDRATE
1) MAIN TEST
PROCEDURE
PRINCIPLE: The copper
content is determined electrolytically
REFERENCE PROCEDURE: -Draft PrEN December 1994 by CEN TC164;
TG415/COPPER SULFATE/21.12.94 -CIPAC 1, 44.0/1/M1/1.2, p.226 (FAO method)
APPARATUS & REAGENTS
Direct current supply (0.1 -1 A)
Tared, perforated, platinum cylinder cathode
Platinum wire anode
Concentrated nitric acid Concentrated sulphuric acid
TEST PROCEDURE
Weigh (to the nearest mg) accurately as rapidly as possibie about 5 g
of a representative sample of copper(ll) sulphate pentahydrate and transfer
it into a 400-ml beaker, washing off the glass balance pan with a stream
of water from a wash bottle. Dissolve the test portion in 350 ml of distilled
water, then add 10 ml of conc. sulphuric acid and 10 ml of conc. nitric
acid.
Deposit the copper elettrolytically on tared, perforated, platinum cylinder
cathode, with a straight platinum wire for the anode. Cover the beaker
carefully with split watch glass to prevent loss by spraying.
Apply a current density of 0.5 A/dm2 of cathode area until deposit is
complete. The cathode area equal gross area of inside of cylinder, including
perforations. It is customary to conduct this operation overnight. When
the solution is colourless, wash down the cover glass, electrodes and
side of beaker, raising the level of the liquid slightly, and continue
the electrolysis for about 15 minutes, noting whether or not copper is
deposited on the newly exposed surface of the platinum. If copper appears,
raise the level of the liquid and continue the electrolysis until none
appears on the electrode.
The completion of electrolysis may be determined by testing a few drops
of the solution on a spot plate with saturated hydrogen sulfide solution.
Electrolysis is complete when no copper sulfide is observed.
When electrolysis is complete, remove (without stopping the current) the
cathode quickly while washing with water from a wash bottle and then rinse
the cathode in two successive baths of 95 percent alcohol. Dry in a oven
at 110 °C for 3 minutes, cool and weigh as metallic copper.
¦ . .
CALCULATION
Cu content (%) = (t / w) x 100
where: t = the increase of the mass of the electrode in grams w = the
mass of the test portion in grams
Purity (%) = Cu content (%) x 3.929
2) ALTERNATIVE TEST PROCEDURE
PRINCIPLE
Cupric ions afford, with potassium iodide, cuprous iodide and iodine.
The latter is
titrated with sodium thiosulfate.
REFERENCE
PROCEDURE: Reagent Chemicals 7th Edition,
American Chemical Society Specifications.
APPARATUS & REAGENTS
¦ Burette 50 ml
Glacial acetic acid
10% sulphuric acid solution
Potassium iodide
0.1 N sodium thiosulfate solution
Potassium thiocyanate
Starch indicator solution
¦
TEST PROCEDURE
Weigh accurately
0.9 to 1.0 g of a representative sample of copper(II) sulphate pentahydrate,
dissolve in distilled water, transfer it into a conical flask and dilute
with distilled water to about 50 ml. Add 4 ml of glacial acetic acid,
1 ml of 10% sulphuric acid and 3 g of potassium iodide. Titrate the liberated
iodine with 0.1 N sodium thiosulfate, adding about 2 g of potassium thiocyanate
and 3 ml of starch indicator solution near the end of the titration. Correct
for a blank.
CALCULATION
One millilitre
of 0.1 N sodium thiosulfate corresponds to 0.02497 g of CuSO4 ? 5H2O
Purity (%)
= t ? 0.02497 ? 100 Copper Content (%) = Purity(%)
w 3.929
where : t
= millilitre used in the titration
w = weight (g) of the CuSO4 ? 5H2O used in the analysis.
|
