EDTA (H ₄ Y) is widely used to identify metals in complexometric (a volumetric analysis where the development of a coloured complex is utilized to indicate the end point of a titration) titrations as it forms stable complexes with many metal ions. EDTA is a tetracorboxylic acid and in alkaline conditions, it exists as Y ⁴ ⁻ ions, which form 1:1 complexes with metal ions like nickel( II) ions:
Y ⁴ ⁻ + Ni ² ⁺ NiY ² ⁻.
A metal ion sign (an organic color which alters colour when it binds with metal ions) shows the end of an EDTA complexometric titration.
Nevertheless, for a metal ion sign to be appropriate in n EDTA titration, it needs to not bind as highly with metal ions as EDTA does. Murexide is for that reason suitable.
The goal of this experiment is to identify the portion of nickel in a nickel( II) salt using EDTA.
Roughly 2.6 g of hydrated nickel( II) sulphate was transferred to a weighing bottle and the contents weighed and about 25cmᶟ of deionised water was contributed to a 100cmᶟ beaker and the nickel moved to the water.
The bottle was weighed without any remaining salt and after that the mix was stirred until the solid was dissolved prior to the resulting service was transferred to a 100cmᶟ standard flask.
The beaker was then rinsed a number of times with deionised water and the rinsings were contributed to the standard flask. The service 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 0.01 moll ⁻¹ EDTA and filled with the exact same option. The 20cmᶟ pipette was washed with a little of the nickel salt option and after that 20cmᶟ of it was pipetted into a conical flask. The service was watered down to about 100cmᶟ with deionised water and murexide indication (around 0.05 g) was contributed to the diluted nickel salt solution in addition to appromimately 10cmᶟ of ammonium chloride service.
The mixture was titrated with the EDTA solution and after and after the addition of about 15cmᶟ the solution was made alkaline by adding approximately 10cmᶟ 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.
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
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
% Mass of Nickel in salt = 0.601675 ÷ 2.60 = 23.14%