"Complexometric Determination of Nickel using EDTA".

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Advanced Higher Chemistry

Unit 2-PPA-1: “Complexometric Determination of Nickel using EDTA”

By Gordon Walker

Introduction:

      Equation of the reaction:

The aim of this experiment is to determine the percentage of nickel present in hydrated nickel sulphate, by Complexometric titration with ethylenediaminetetraacetic acid (EDTA). The aim will be carried out using a basic Complexometric titration of EDTA into a solution of nickel sulphate, until the equivalence point is reached i.e. when a colour change is observed. EDTA is a substance used successfully as a lignant, and this is due to its structure in alkaline conditions (which can be seen in figure 1.1). As a consequence of its structure the EDTA is able to form stable complexes with metal ions such as nickel, because it has the capacity to accept other ions (in this case Ni   ), as seen in figure 1.2.

The percentage of nickel in nickel (    ) sulphate  (NiSO  .6H O), is given by the following calculation:

1 mol:  NiSO  . 6H  O          =   58.7 + 32.1 + (16x4) + 6 ( (2x1) + 16)

=   154.8                         + 108

=    262.8g

Therefore:  % of Nickel in NISO  .  6H  O

= 58.7 / 262.8 x 100

=22.3%

Figure 1.1                                                                Figure 1.2

Procedure:

 The next stage of the experiment was the practical procedure stage (as shown in figure 1.3), which was carried out in the following manner:

  1. I carefully weighed out 2.6g of hydrated nickel sulphate using a weighing bottle
  2. Next I added the nickel salt to a 100cm beaker and added 25cm of deionised water, and then reweighed the bottle to determine if any weight should be deducted for calculation purposes (a negligible weight was left in the bottle).
  3. Next I stirred the solution until the solid was fully dissolved, then transferred the solution to a 100cm standard flask.
  4. For the next step in the procedure I rinsed the beaker with deionised water, and repeated several times until the solution was nearly at the graduation mark, then using a dropper I made it up to the graduation mark, inverting the solution several times to ensure a proper mix.
  5. After rinsing the burette with some EDTA (10 mol l), and filling it with EDTA till it was full, I then proceeded to also rinse the pipette with a little nickel salt.
  6. I then pipette 20cm of the nickel salt solution into a conical flask, and diluted the solution to 100cm with deionised water
  7. Next I added 0.05g of murexide indicator to the diluted salt along with 10cm of ammonia chloride solution
  8. I then proceeded to titrate in 15cm of the EDTA, and then add 10cm of 0.88 agueous ammonia.
  9. I continued the titration till I observed a colour change (to a blue-violet colour). This is the equivalence point.
  10. I repeated my titration to achieve a concordant result, and fortunately my second titration proved to produce the same result as the first.
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Figure 1.3

∙The next part of my procedure was calculation of the following:

      The percentage by mass of nickel in the hydrated nickel (  ) sulphate:

2.6g NiSO  . 6H  O in 100cm  H  O and titrated 20cm portions with 0.1 mol EDTA.

19.7cm of EDTA was used in the titration

Number of moles = CxV

                             = 0.1 x ...

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