Gravimetric determination of Nickel using Dimethylglyoxime
Gravimetric analysis is one of the most accurate analytical methods available. It is concerned with the determination of a substance by the process of weighing. The element to be determined is converted into a stable compound of definite composition and the mass of the compound is determined accurately. From this, the mass of element is calculated. The gravimetric analysis involves a) precipitation b) filtration c) washing of the precipitate and d) drying and weighing of the precipitate. Advantage:  Conducted with simple apparatus.  Interpretation of results is easy and readings are directly related to analyte amount.
Gravimetric determination of nickel using dimethylglyoxime Gravimetric analysis can be used to determine the nickel content of a nickel(II) salt. This can be achieved by precipitation of nickel as nickel dimethyl glyoxime by adding alcoholic solution of dimethyl glyoxime C4H6(NOH)2 and then adding a slight excess of aqueous ammonia solution:
H
H O H3C
2 H3C
N C C
H 3C
+ Ni2+ N O
H Dimethylglyoxime
pH >5
H 3C
O
O
N
N
C C
C
Ni N
N
C
CH3 + 2H+ CH3
O
O H Nickel(II) dimethylglyoximate
The above reaction occurs due to donation of the electron pairs on the four nitrogen atoms, not by electrons on the oxygen atoms. The reaction is performed in a solution buffered by either an ammonia or citrate buffer to prevent the pH of the solution from falling below 5. If the pH does become too low the equilibrium of the above reaction favors the formation of the nickel (II) ion, causing the dissolution of Ni (DMG) 2 back into the mother liquor.The complex, nickel(II) dimethylglyoximate, is filtered from the reaction mixture, dried and weighed. Nickel content is calculated stoichiometrically from the weight of the precipitate
FT-IR spectroscopy can be used forcharacterisation of the Nickel(II)
dimethylglyoximate complex Labwares, Chemicals and Reagents:
                 
500 cm 3 beaker sintered glass crucible Buchner flask and adapter Vaccum pump desiccator balance (preferably accurate to 0.001 g) weighing bottle hot plate Water bath measuring cylinders (10 cm 3 and 100 cm 3 ) thermometer stirring rod dropper oven Nickel(II) chloride (NiCl 2 .6H 2 O) dimethylglyoxime in ethanol (0.1 mol l –1 ) 2 mol l –1 hydrochloric acid 2 mol l –1 ammonia
Procedure 1. 2. 3. 4. 5. 6.
7. 8. 9. 10.
11.
Weigh approximately 0.1 g of hydrated nickel(II) chloride . Weigh the dry sintered glass crucible. Add about 4 ml of deionised water to a 100 ml beaker and transfer the bulk of the nickel salt to the water. Stir the mixture until the solid dissolves and add about 4 ml of 2 mol l –1 hydrochloric acid. Dilute the mixture with deionised water to about 40 ml. Heat the solution to 70–80°C on a water bath for ~10 min and add approximately 10 ml of 0.1 mol l –1 dimethylglyoxime in ethanol. Add 2 mol l –1 ammonia solution dropwise and with constant stirring until a permanent red precipitate is obtained. Add a further 2 ml of the ammonia solution to provide a slight excess. Heat the beaker and contents on a water bath for about 10 minutes Remove the beaker from the water bath and allow it to cool to room temperature . After precipitate has settled test the clear liquid for complete precipitation by adding a few drops of the dimethylglyoxime and ammonia solutions. Set up the filtration apparatus: sintered glass crucible, Buchner flask and adapter. Filter off the precipitate at the water pump and wash the precipitate with a several portions of deionised water. Dry the crucible and precipitate in the oven at 120 °C.
12. 13. 14. 15.
Remove from oven and once they have cooled to room temperature, reweigh the crucible and contents. Calculate the percentage by mass of nickel in the sample of the hydrated nickel(II) chloride. Calculate the theoretical percentage by mass of nickel in NiCl 2 .6H 2 O and compare this with the experimental value. Account for any difference. Carefully preserve the Ni(II)(DMG) 2 complex for studying FR-IR.
Precaution: Wear eye protection and if any chemical splashes on the skin, wash it off immediately. Hydrated nickel(II) chloride is harmful by inhalation and by ingestion. Wear gloves. Dimethylglyoxime in ethanol is irritating to the eyes and is highly flammable. 2 mol l –1 ammonia irritates the eyes.
Be concerned: • To quantitatively collect all the precipitate • To know the exact composition of precipitate • To avoid loss of material during the handling/processing of sample. • To determine mass accurately and precisely
Calculations for Reagent preparation 2 M HCL (50 ml):
0.1 M Dimethylglyoxime (50 ml):
Calculations for Nickel Determination:
Weight of Nickel(II)chloride salt
Weight of dry sintered glass crucible
Mass of sintered glass crucible + Nickel complex
Mass of dimethyl glyoxime nickel complex (g)
Mass of Nickel in _______ g of complex =
References : Books:  Textbook of macro and semimicro qualitative inorganic analysis by Vogel.  Methods of Quantitative Inorganic Analysis by Kodama, Kazunobu.  Principles of Chemical Analysis by Mohd. Marsin Sanagi, Azli Sulaiman, Wan Aini Wan Ibrahim. Research Articles:  Is There Ni in My Liquor? A Hands-On Laboratory Exercise for Relating Chemistry to Extractive Metallurgy, Damian W. Laird and David J. Henry J. Chem. Educ. 2013, 90, 1671−1674.  The gravimetric determination of nickel with dimethylglyoxime in the presence of copper. Claassen and L. Bastings. Anal. Chem., 1959, 165, 134.  The determination of nickel by precipitation with dimethylglyoxime. J. T. Minster, Analyst, 1946,71, 424-428.