Determination of nickel Essay

INTRODUCTION EDTA (Hâ‚„Y) is widely used to determine metals in complexometric (a volumetric analysis where the formation of a coloured complex is used to indicate the end point of a titration) titrations as it forms stable complexes with most metal ions. EDTA is a tetracorboxylic acid and in alkaline conditions, it exists as Y⠁ ´Ã¢  » ions, which form 1:1 complexes with metal ions like nickel(II) ions: Y⠁ ´Ã¢  » + Ni ²Ã¢  º NiY ²Ã¢  » A metal ion indicator (an organic dye which changes colour when it binds with metal ions) shows the end of an EDTA complexometric titration. However, for a metal ion indicator to be suitable in n EDTA titration, it must not bind as strongly with metal ions as EDTA does. Murexide is therefore suitable. AIM The aim of this experiment is to determine the percentage of nickel in a nickel(II) salt using EDTA. Approximately 2.6g of hydrated nickel(II) sulphate was transferred to a weighing bottle and the contents weighed and about 25cmá ¶Å¸ of deionised water was added to a 100cmá ¶Å¸ beaker and the nickel transferred to the water. The bottle was weighed without any remaining salt and then the mixture was stirred until the solid was dissolved before the resulting solution was transferred to a 100cmá ¶Å¸ standard flask. The beaker was then rinsed several times with deionised water and the rinsings were added to the standard flask. The solution was filled up to the graduation mark with deionised water and the flask was stoppered and inverted several times to mix the contents. The burette was rinsed with 0.01moll⠁ »Ã‚ ¹ EDTA and filled with the same solution. The 20cmá ¶Å¸ pipette was rinsed with a little of the nickel salt solution and then 20cmá ¶Å¸ of it was pipetted into a conical flask. The solution was diluted to about 100cmá ¶Å¸ with deionised water and murexide indicator (approximately 0.05g) was added to the diluted nickel salt solution along with appromimately 10cmá ¶Å¸ of ammonium chloride solution. The mixture was titrated with the EDTA solution and after and after the addition of about 15cmá ¶Å¸ the solution was made alkaline by adding  approximately 10cmá ¶Å¸ of 0.88 aqueous ammonia (concentrated ammonia solution). The titration was then continued to the end point, shown by the first appearance of a blue-violet colour. Titrations were repeated until two concordant results were obtained. RESULTS Mass of 1 Mole of NiSO4.6H2O: 262.8g Mass of 1 Mole of Ni: 58.7g Theoretical Percentage by Mass: Volumes of EDTA used in titration: 1st : 20.2cm3 2nd: 20.9cm3 3rd: 20.4cm3 Average: 20.5cm3 Moles of EDTA used = 0.1 x 0.0205 = 0.00205 Moles EDTA reacts with Nickel in a 1:1 ratio, so the number of moles of Nickel in 20cm3 of the salt solution = 0.00205Moles Number of Moles in 100cm3 = 0.00205 x 5 = 0.01025 Moles Number of Moles of Ni2+ in 2.6g of Nickel salt = 0.01025 Weight of Ni2+ in salt = 0.01025 x 58.7 = 0.601675g CONCLUSION % Mass of Nickel in salt = 0.601675 à · 2.60 = 23.14%