Electrochemistry report, Lab Reports of Electrochemistry

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Electrochemistry Laboratory Report

• Introduction
• Materials and Methods
• Results and discussion
• Conclusion
• References

• 𝑒 − ⇔ 𝑀 In equation 1, 𝑥is the number of bound ligands needed to form the stable complex. And this value is important to determine the stability constant of the complex relating the concentrations of the complex, metal and ligand, as equation 3 shows. (Frenzel, 2021) β𝑥= (3) [𝑀𝐿𝑥] [𝑀+][𝐿−]𝑥 The Nernst equation (eq. 4) can be used to evaluate the reduction potential ( 𝐸1/2) and when the stability constant is large enough, the complex can be formed. After some mathematical manipulation it results in eq. 5, which describes the change in potential ( ∆𝐸 ) (Ashworth, 1/ Frisch, 2017). 𝐸 = 𝐸 (4) θ − 2.303𝑅𝑇 𝑛𝐹 𝑙𝑜𝑔^ [𝑀] [𝑀+] ∆𝐸 (5) 1/

2.303𝑅𝑇 𝑛𝐹 𝑙𝑜𝑔β𝑥 −^ 2.303𝑅𝑇𝑥 𝑛𝐹 𝑙𝑜𝑔[𝐿 − ] Aim Use differential pulse voltammetry (DPV) to determine the reduction potential of the 𝐼𝑛

redox couple at various sulfate concentrations. Produce a plot of changing potential against ligand concentration to determine the speciation and stability of indium.

2.Materials and Methods

In order to perform the analysis, the following set of electrodes was used, shown in figure Fig. 2. Example of a set of electrodes for differential pulse voltammetry analysis. Source: SINReM Electrochemistry Practical 2021. Where: WE is the working electrode (Hg), RE is the reference electrode and CE is the counter electrode. The solutions provided to start the experiment were

Sample: 1 mM In(ClO4)3 in 10 mM HNO3 + 1 M KNO Titrant: 1 mM In(ClO4)3 in 10 mM HNO3 + 1 M Na2SO And the parameters are shown in Table 1. Table 1. Parameters for DPV experiment. purge time 300 s start potential –0.4 V end potential –0.7 V step potential 0.001 V modulation amplitude 0.025 V modulation time 0.050 s The titrant volume, concentration of [𝑆𝑂 4 and the purge time were also specified, as Fig. 3 − ] shows. Fig. 3. Description of titrant volume, concentration and purge time. Source: SINReM Electrochemistry Practical 2021.

Fig. 5. Graph of 𝑙𝑜𝑔[𝑆𝑂 4 / M versus ΔEp1/2 / V for the complex formation with and. − ] 𝐼𝑛

[𝑆𝑂 4 − ] The curve which describes the complex formed (with absolute larger slope) is 𝑦 =− 0. 0182𝑥 − 0. 0317. From the slope it was calculated the number of bound ligands ( ) 𝑥 and from the linear coefficient it was calculated the stability constant ( 𝑙𝑜𝑔 10 β𝑥). The results are shown in table 3. Table 3. Results of number of bound ligands and stability constant.

𝑥 𝑙𝑜𝑔 10 β𝑥 0.62 5. The change in potential ( ∆𝐸𝑝1/2/𝑉) remains near 0 for the first 3 concentrations of sulfate, suggesting that no complexation is occurring yet. Then, when the potential became more negative, it was possible to calculate the number of ligands and the stability constant since this behavior of the curves suggests that the complex was being formed. Despite the difference between the results and literature (Ashworth and Frisch, 2017), the most reasonable approximation for 𝑥would be 1, suggesting that only 1 sulfate is bounded in the complex with indium. And for the stability constant it is clear that the value is higher than literature, it is only plausible to state that a stable complex was formed at this point of the graph.

4.Conclusion

It was possible to determine the variables number of bound ligands ( ) and the stability𝑥 constant ( 𝑙𝑜𝑔 10 β𝑥) by plotting the reduction potential of In at various sulfate concentrations and then extracting the slope and linear coefficient to calculate the variables. When compared to literature, the values found were different (lower for x and higher for 𝑙𝑜𝑔 10 β𝑥), we think this is due to the number of points for the flat part of the graph (before complexation starts). Therefore, more data collection could be made in order to confirm or not the results.

5.References

Ashworth, C.; Frisch, G. Complexation Equilibria of Indium in Aqueous Chloride, Sulfate and Nitrate Solutions: An Electrochemical Investigation. J Solution Chem, 2017, 46:1928–1940.