The burette was rinsed with 0.10 mol/l EDTA and filled with EDTA solution after that a 20cm³ pipette was rinsed with nickel salt solution and 20cm³ of nickel salt was pipetted into a conical flask and was diluted to 100cm³ by adding deionised water. A pinch of murexide indicator and 10 cm³ of ammonium chloride solution were added to it as well. Then the nickel salt was titrated with the EDTA, after 15cm³ of EDTA had been added to nickel salt 10cm³ of 0.88aqueous ammonia was added to it to make the solution alkaline. 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 mole of nickel = 58.7g
0.01145 moles = 0.01145*58.7g = 0.672g
% mass of nickel in 2.6g nickel salt = (0.672/2.6)*100
= 25.76%
Uncertainty
Uncertainty in measurement:
Burette reading - ± 0.1 [class B 50cm³]
Pipette reading - ± 0.06 [class B 20cm³]
Balance reading - ± 0.1g
Concentration of EDTA - ± 0.0003 mol/l
Average titre = 22.9cm³
Mass of nickel salt = 2.6g
Uncertainty calculation
Uncertainty in mass of nickel sulphate = 0.02g
% Uncertainty = (0.02/2.6) *100 = 0.77%
Uncertainty in volume of nickel sulphate (aq) 100cm³ flask[class B] = 0.2cm³
% Uncertainty = (0.2/100)*100 = 0.20%
Uncertainty in pipette volume of nickel sulphate (aq)20cm³ [class B] = 0.06cm³
% Uncertainty = (0.06/20)*100 = 0.30%
% Uncertainty in concentration of EDTA = (0.0003/0.1)*100 = 0.30%
Uncertainty in titre volume of EDTA (50cm³ burette class B) = 0.1cm3 + end point judgement = 0.05cm³ = 0.15cm³
% Uncertainty in titre volume of EDTA = (0.15/22.9)*100 = 0.74%
Therefore % Uncertainty in %of nickel = 0.77+0.20+0.30+0.30+0.74 = 2.31%
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:
- The measurement of mass of nickel sulphate.
- The measurement of burette and pipette reading due to use of class B equipment with high uncertainty value.
- 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
- Use of class An equipment in place of class B as their uncertainty value is lesser than class B and are more accurate.
- Use of more accurate balance.
- Use of deionised water.
by
rahul007 (student)
