Lab Repot Analytical 1

TITLE: GRAVIMETRIC DETERMINATION OF NICKEL  Abstract- The objective of the study was to determine the nickel by using gravimetric method. After this experiment was carried out, the sample color that initially in white solid turns to red solid. Therefore, t he nickel is in red color. Keyword: Gravimetric Method

INTRODUCTION Dimethylglyoxime (DMGH) is an organic precipitant principally  used to determine nickel. DMGH selectively reacts with nickel at a controlled PH of between 5 and 11. The formation of chelate between nickel (II) ion and dimethylglyoxime can be written as: Ni2+ + 2H2DMG

Ni(HDMG)2 + 2H

+

DMGH is almost insoluble in water and is added in the form of 1 per cent solution in 90% ethanol; 1 ml of this solution is sufficient for the precipitation of 0.0025 g of nickel. The precipitation formed is so bulky  that the presence of a very small amount of nickel can be handled conveniently. Nickel is normally precipitated by adding DMGH reagent to a hot acidic solution of nickel, which is then made basic by addition of  ammonia. Only a slight excess of reagent should be used , since dimethylglyoxime is not very soluble in water or in very dilute ethanol and may precipitate; if very large excess is added (such that the alcohol content of the solution exceeds 50 per cent ), some of the precipitate may  dissolve.

EXPERIMENT 50 ml of sample solution A is pipette into 100 ml volumetric flask, it was diluted to the mark with distilled water and it is mixed thoroughly. 25 ml aliquot sample are transferred into three 250 ml beakers. To each replicate, 100 ml distilled water are added and they are heated up to 80°C. Then, it was removed from hot plate. Next, 10 ml DMG (1% in alcohol) is added slowly and stirred vigorously into the solution while maintaining the high temperature. The mixture was checked with litmus paper to determine whether the solution is acidic or not. If it’s not acidic, HNO3 (6M) is added drop wise. Approximately 3 g of urea is added into each beaker and it is stirred again. The mixture is heated up to boil for 2-3 minutes and then it is cooled to room temperature. Next, the crucibles are cooled in the desiccators and it is weighed to the nearest

0.1 mg. When the mixture has cooled down, a few drops of dilute NH 4OH is added. Most of supernatant liquid was decanted (separated) and each replicate is filtered through sintered crucibles by using suction filtration.  The precipitate was washed with two or three portion of 10 ml distilled water. The crucible is dried and precipitated it in the microwave oven at medium power for 4 minutes. Then, they are cooled in desiccators and is being weighed. The drying process is repeated twice or more until constant weight is obtained. The weight (g) of nickel in each replicate is weighed and the average ppm ± S.D of Ni in the sample