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Experiment 7
Experiment 7
Aim of the Experiment
Aim of the Experiment
To estimate gravimetrically nickel as nickel dimethyl glyoximate in given solution.
Principle
Principle
Nickel is almost invariably determined by precipitationwith dimethyl-glyoxime from a neutral or ammoniacal solution. The sparingly soluble precipitate is scarlet in colour. After being dried, it is weighed.
Solution :
Solution for such an exercise may be prepared by dissolving 16.06 g of nickel ammonium sulphate [NiSO4 (NH4)2SO4.6H2O]per litre. 25 ml of this solution will give about 0.3 g of dry precipitate of dimethyl glyoximate.
Reagent:
(i) Precipitating reagent : It is 1% solution of dimethyl-glyoxime in alcohol which can be prepared by dissolving 1 g of dimethyl glyoxime in 100 ml of alcohol.
(ii) Ammonia solution: It is 1:1 ammonia solution which may be prepared by adding 50 ml of liquor ammonia to 50 ml of distilled water.
(iii) Washing solution : Distilled water heated to 70-80°C is used as a
washing solution.
Ni-DMG 1 PREPARATION.mp4Ni-DMG 2 PREPARATION.mp4
Procedure
(i) Precipitation : Measure out 20 ml of the given solution with the help of standard burette into a 400 ml beaker. To this add 100 ml of distilled water and 1 ml of methyl red. Now add dil. NH4OH solution dropwise to neutralise mineral acid with stirring till the colour of the solution changes from red to yellow. Add dil. acetic acid to make the solution acidic i.e., the colour of the solution changes from yellow to red. Heat the solution just to about 70–80°C. Then add 30 ml of 1% dimethylglyoxime with constant stirring. Now go on adding 1:1 ammonia solution dropwise till the solution becomes alkaline i.., the colour of the solution changes from red to yellow. Digest the ppt on steam bath for about an hour. Then test for complete precipitation by adding few drops of dimethylglyoxime solution to the clear supernatant liquid. After this cool the solution for one hour.
(ii) Filtration and washing : Transfer the supernatant liquid to a weighed sintered crucible (Grade G-3). Wash the ppt. three or four times with the hot water and transfer these washing to the crucible. Then transfer the ppt, to the crucible, making use of a 'policeman' to remove any adhering ppt. from the beaker. Wash the ppt on the sintered glass crucible with hot water until the washings are free from Cl- and SO2-ions.
(iii) Drying: Now dry the ppt. at 110-120°C in an electric oven for about an hour. Cool the crucible in the desiccator and weigh. Repeat this process of the heating, cooling and weighing until the constant weight of crucible is obtained.
Calculations
Let weight of ppt. be x g
Now we know,
Ni(C,H,02N2) = Ni
288.9112 =58.69
.: 288.9112 g of nickel dimethylglyoxime contains
= 58.69 g of nickel
:: x g of nickel dimethylglyoximate contains =58.69/288.9112 X x
=
=
25 ml of the given solution contains = 58.69 X x / 281.9112 g of nickel
=
=
1000ml of given solution will contain = (58.69 X x / 281.9112) X (1000/25) g of nickel
=
=
Result:
The supplied solution contains _________ g of nickel per litre.
Questions
Questions
1. What is precipitation in gravimetric Analysis?
2. Why we perform incineration in gravimetry?
3. Why do we use Whatman's filter paper for gravimetric analysis of Barium?
4. What is coprecipitation?
5. What do we mean by post precipitation?
Developed by
Developed by
Dr. Mriganka Das,
Assistant Professor, Chemistry,
mriganka.das@gsfcuniversity.ac.in
Ms. Khyati Joshi
Teaching Assitant , Chemistry
khyati.joshi@gsfcuniversity.ac.in
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