Cha

SEPARATION AND ESTIMATION

OF TWO METAL IONS
*********** ** ****************************'.

4.1 coPpER-NICKEL
Estimation of both by gravimetric method
rinciple: n a mixed solution of boti, copper is estimated first as cuprous thiocyanate
Cusand then in the filtrate, niekel is estimated as nickel dimethyl glyoximate
iDMG). Copper is precipitated as cuprous thiocyanate from a mixed solution of copper
and nicke by, adding ammonium thiocyanate solution in sightly acidic medium in the
presence of reducing agent such as sulphurous acid to reduce Cu (1) to Cu ()

2Cu HSO HO 2Cu +HSOj +2H

2Cu+SCN 2CusCN
White ppt.
Ater removing copper, dimethyl glyoxime reagent (1% solution of dimethylglyoxime in
ethanol) is added to hot slightly acidic filtrate followed by slight excess of ammonua soluion.
Scarlet red coloured precipitate of nickel dimethylglyoximate is formed.

H3C-CN NC-CH3
Ni +2 H3C-C=NOH +2H
HC-C-NOH
(HDMG)
HC-C=N N-C-CH3

H
Scarlet-re NiHDMG}
-ted ppt.

Chemical required: 50 mL mixed solution of copper sulphate and Nickel ammonium

Sulphate. (25 mL copper sulphate (16 8/L) and 25 mL nickel ammonium sulphate (11 g/1).
10% Ammonium
thiocyanate solution.
Saturated sulphurous acid solution.
1% solution of dimethylglyoxime in ethanol.

(I-34)
Cental
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 I-35
SEPARATION AND ESTIMATION OF TWO METAL IONS

1:1 ammonla solution.

beaker. Add
dil. HC, aquaregia. solution in 400 mL
estimation: Take 50 mL mixture saturated sulphurous
Procedure for copper a e x c e s s of (-20 mL) treshiy
prepared
then slight add freshly prepared
-smL ot
dil.
HCl and to about 150 mL.
Heat it to
boilin8 and
this solution till complete precipitation
acid solution. Dilute
thiocyanate
solution slowly
with constant
compiete
stirring
Test tor
10
ammonum
white precipitate
to settie.
of cuprous tniocyanate
supernatant liquid by
Occurs. Alow the thiocyanate scolution
to
the clear a
ammonium precipitate through
precipitationi by adding
Allow the precipitate to settle for
2-3 hrs.
Filter the ammonium
of glass rod. c o i d a n d dilute
means 2 3 times with
sintered glass crucible, wash the ppt diluted to 100 mL and
weighed G, ammonium
thiocyanate
solution
ot 10% with cold
thiocyanate
solution (1 mL wash the precip.tate
acid solution). Finally
dded with 5-10 drops ot sulphurous ot ammonum Dry
thiocyanate. the
w i t h 20%
ethanol to
remove
excessthen
distilled w a t e r and then in a disiccator and weigh to constant weight.
a

at 100-110C m oven, cool

precipitate estimation of nickel.
for the gravimetric
reserve the iltrate
and washings
Keep
Calculations:

(a) Weight of sintered glass

crucible
-W18
W28
-

of sintered glass crucible + precipitate

(6) Weight
(c) Weight of C u s C N precipitate = ( W - Wi8

CusO 5H;O
24271
*
Weight or CuscN
of
Weight coPper216
2497 weight of CuSCN.
Weught of coPper sulphate 1 21

Precautions: A large excess of the precipitant (ammonium thiocyanate) should bee

a 1on. Jhe solution
complex thiocyanate
avoided, since CusCN is soluble in its forming
excessIike etc.
also must be free torm any oxidising agent HNOg
Estimation of Nickel
to a beaker and
Transfer the filtrate and washings
the solution
evaporate to about 10 mL
Heat this solution with about 20-25 mL aquaregia to almost dryness on a sand bath. 1nis w
add
of
thiocyanate (added in excess during copper estimation). 1o his 100
destroy the excess
mL of distilled water and 1 mLof dil. Hci. Heat the solution to about 70"C, add slight excess of
1% dimethylglyoxime reagent followed by addition of dilute ammonía solution dropwise with
tor
the precipitate on water bath
constant
about
stirring till the solution becomes ammoniacal. Digest
30 minutes. Test the supernatant liquid tor complete precipitation. Futer the precipitate

weighed sintered crucible(G4). Wash the precipitate with hot water until
through a
previously trom ions. it in oven at 110 -120°C, cool in disiccator and a
the washings are Iree chloride Dry
and weighing till constant weight is obtained.
weigh. Repeat the heating, cooling a

Calculations
(a) Weight of sintered 8lass crucible =
Wi 8
(b) Weight of crucible+ precipitate =
W2 &
Creald trom lebouku o 2019 050U 22 59 45
 1-36 ADVANCD PRACTICAL OHEMIST2Y
( ) weight of nuckei dimethyiglyoxumate = ( 2 -W)8

iC4H0N); NISO (N) SO 6H,0

Hence,

Weight ot 8-6 weight of preipitate (W2 - W)

2589

Weight of Nickel ammonium sulphate ( , - W)

90

4.2 BARIUM-COPPER
Estimation of barium
gravimetrically and copper volumetrically
Principle : In a mixed solution of both, barium is estimated first as barium sulphate and
then t h e tate. copper Is estimated as Cuo5HO 1odometrically by tiratnng against
SOuium thOsuiptiate solufion using potassium iodide and starch as an indicator.

ariu um is Precipitated as barium sulphate from the mixed solution of barium and copper

by adding dil. H5O, In hot soluion

BaCi +H2SO4 BaSO, 2HCI

whute Ppt

ng barium copper is estimated iodometrically in the filtrate. In this process

when a soiution of potassium iodide is added to the copper sulphate solution, tree ioaune is

liberated
2CuSO, *4KI
2Cul *2K,SOP
2Cul
The liberated iodine oxidizes the Cultetrathionate.
thiosulphate to

Hence
2Na5,0 * Na:S,0, +2Nal
2Cuso,l = 2Na2S20s
Here starch solution is used as indicator and
at the end blue colour due to
point presence
of l disapPpears and the solution becomes milky white.

Chemicals required:
30 mLmixed solution of copper and barium (25 mL copper solution20 g copper foil
dissolved in minimum conc. HNO, and diluted to 100W mL and 25 ml. BaCi 2.2H,0 solution
(8g/L)
2N H2S0, (AR grade)
10% KI solution

1% starch solution

AboutntermediateHyposolution.
Standard3 OPper su.phate solution.
d i l Hd (AR grade)
U r e a (AR grade)

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