"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.
0.01g = 0.01g + 0.01g = 0.02g = 0.02/2.60 x 100 = 0.77% error Flask = 0.2cm = 0.2/ 100 x 100 = 0.2% error Pipette = 0.06cm = 0.06/20 x 100 = 0.3% error Burette = 0.1cm = 0.1/19.7 x 100 = 0.51% error EDTA = 0.1% Total Error in experiment: 1.88% Absolute uncertainty = 1.97/ 100 x 22.4 = 0.438% Safety: * Wear gloves and goggles at all times during the experiment * Nickel sulphate is harmful to swallow and inhale, irritates eyes and skin (can cause dermatitis) *EDTA is toxic but only in large doses *Ammonia is toxic if inhaled and if swallowed. Ammonia burns skins and does internal damage if ingested Results Titration 1 (cm ) Titration 2 (cm ) Average Titration (cm ) 19.7 19.7 19.7 From our experimental data we have discovered that our value for the percentage of nickel in hydrated nickel sulphate was very nearly the theoretical value given, thus indicating a successful experiment, and consequently we did not have to redo the entire experiment. Also using the absolute uncertainty that we previously calculated we were within the experimental error range proving the experiment to be a success. From our experiment we managed to titrate in 19.7cm of EDTA before we reached the equivalence point, and we achieved this result concordantly after two attempts. Experimental percentage value of Ni in nickel sulphate = 22.4% Theoretical percentage value of Ni in nickel sulphate = 22.3% FINAL ANSWER/RESULT = 22.4% 0.438%
If an old bottle of EDTA was used or if and old sample of Nickel ( ) sulphate was used then this would also alter the values given, and consequently or calculations. These errors are extremely hard to rectify, but can be lessened by the experiment being repeated several more times, then taking an average, this would be one way of improving the experiment. Using "class A" equipment and using very fresh samples of the chemicals could also improve the experiment. The method used to calculate the percentage of nickel was an accurate way of calculating because titration is done precisely and little by little, but once again could have been improved by the usage of scales that were smaller in range and bigger in spacing. Also the balance used in this experiment was accurate but again a much more accurate balance that was more sensitive could have improved the result. Also the use of murexide indicator in the experiment was a good idea, because in order for the EDTA titration to work (i.e. for the EDTA to bind with the Ni ions) the indicator has to bond with less force to the EDTA than the metal ions in order for the combining of the metal ions onto the EDTA complex to successfully take place. Since murexide indicator binds weakly with EDTA complex then it is a very good indicator to use. Also so the fact that it allows us to observe a very noticeable colour change also shows its relevance as a good indicator for this experiment.
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