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The aim of the experiment is to determine the percentage of nickel present in hydrated nickel sulphate by Complex metric titration with EDTA

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Introduction

UNIT 2 - PPA 1 - Complexometric Determination of Nickel Using EDTA AIM The aim of the experiment is to determine the percentage of nickel present in hydrated nickel sulphate by Complex metric titration with EDTA. The aim will be achieved by compleximetric titration of EDTA into a solution of nickel sulphate until a colour change is observed. EDTA act as a ligand because of its structure in alkaline conditions it is able to form stable complexes with metal ions such as nickel as it has the capacity to donate electron and it has six lone pair of electrons which forms an octahedral complex in a 1:1 ratio with Ni2+ or metal ions. Ni2+ (aq) + EDTA2- (aq) â Ni-EDTA (aq) The percentage mass of nickel in nickel sulphate is given by the following calculation. 1 mol of nickel sulphate (NiSO4.6H2O) = 58.7 + 32.1 + (4*16) + 6(2*1) + 16) = 262.8g % mass of nickel = 58.7 / 262.8 * 100 = 22.33% PROCEDURE Approximately 2.6g of hydrated nickel sulphate was weighed using a weighting bottle, and 25cm³ of deionised water was transferred in a 100cm³ beaker followed by 2.6g nickel sulphate. ...read more.

Middle

When approximately 20cm³ of EDTA had been added to the nickel salt the titration was continued by adding EDTA drop by drop to the nickel salt until the end point was reached i.e. appearance of a blue-violet colour. Detection of the end point was quite difficult so a titrated solution was kept as a sample to match the end point of the following titration. The titration was continued until two concordant results were achieved. Safety measure Goggles and gloves were used during the experiment as a safety measure due to toxic nature of aqueous ammonia and hydrated nickel sulphate and other chemicals as they could cause irritation to the eyes and skin. RESULT Titration result Reading Titre1 (cm³) Titre2 (cm³) Titre3 (cm³) Initial 0 5.0 7.8 Final 25.2 27.8 30.8 EDTA used 25.2 22.8 23.0 Titre2 and titre3 are concordant Average = (22.8+23.0)/2 = 22.9 cm³ Calculation EDTA Nickel Concentration = 0.1mol/l n of moles of EDTA = n of moles of nickel Volume = 22.9cm³ 20ml = 0.00229 moles N = c*v 100ml = 0.01145 moles = 0.1*22.9)/1000 = 0.00229 moles 1 ...read more.

Conclusion

Absolute uncertainty in % of nickel = (2.31*25.76)/100 = 0.57% % of nickel in nickel sulphate from experiment is 25.9 ± 0.57% CONCLUSION The percentage mass of nickel in the sample of nickel sulphate is 25.9 ± 0.57% which is bigger compared to the theoretical value of 22.3%. Analysis of the uncertainty shows that the value is near to the error boundaries which is calculated for the type of apparatus used. Main source of errors: 1. The measurement of mass of nickel sulphate. 2. The measurement of burette and pipette reading due to use of class B equipment with high uncertainty value. 3. The end point judgment of the colour change. Murexide a suitable indicator Murexide is a suitable indicator for titration of nickel using EDTA as it bind with metal ions less strongly than EDTA & it changes colour when it bind with metal ions. Possible improvements 1. Use of class An equipment in place of class B as their uncertainty value is lesser than class B and are more accurate. 2. Use of more accurate balance. 3. Use of deionised water. ...read more.

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