EDTA (HÃ¢ÂÂY) 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 YÃ¢ÂÂ´Ã¢ÂÂ» ions, which form 1:1 complexes with metal ions like nickel(II) ions:
YÃ¢ÂÂ´Ã¢ÂÂ» + NiÃÂ²Ã¢ÂÂº NiYÃÂ²Ã¢ÂÂ»
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.
The aim of this experiment is to determine the percentage of nickel in a nickel(II) salt using EDTA.
50cmÃ¡Â¶Â burette Ã¢ÂÂGlass stirring rod
20cmÃ¡Â¶Â pipette Ã¢ÂÂHydrated nickel(II) sulphate (NiSOÃ¢ÂÂ.6HÃ¢ÂÂO)
100cmÃ¡Â¶Â standard flask Ã¢ÂÂStandardised 0.10mollÃ¢ÂÂ»ÃÂ¹ EDTA solution
250cmÃ¡Â¶Â conical flask Ã¢ÂÂ1 mollÃ¢ÂÂ»ÃÂ¹ ammonium chloride
Weighing bottle Ã¢ÂÂMurexide indicator
Balance (accurate to 0.01g) Ã¢ÂÂ0.88 aqueous ammonia
100cmÃ¡Â¶Â beakers Ã¢ÂÂDeionised water
25cmÃ¡Â¶Â measuring cylinder
Approximately 2.6g of hydrated nickel(II) sulphate was transferred to a weighing bottle and the contents weighed and about 25cmÃ¡Â¶Â of deionised water was added to a 100cmÃ¡Â¶Â 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 100cmÃ¡Â¶Â 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...