What is the electrode potential at the equivalence point if concentrations of titrant and titrand are going to be zero? - Chemistry Stack Exchange most recent 30 from chemistry.stackexchange.com 2019-08-20T16:28:01Z https://chemistry.stackexchange.com/feeds/question/103577 http://www.creativecommons.org/licenses/by-sa/3.0/rdf https://chemistry.stackexchange.com/q/103577 1 What is the electrode potential at the equivalence point if concentrations of titrant and titrand are going to be zero? Sashank Sriram https://chemistry.stackexchange.com/users/17593 2018-10-29T09:45:14Z 2018-10-29T13:36:28Z <p>Let's assume that the titrand is <span class="math-container">$\ce{Fe^2+}$</span> and the titrant is <span class="math-container">$\ce{Cr2O7^2-}$</span>. Then</p> <p><span class="math-container">$$E = E^\circ_\ce{Fe^{2+}/Fe^{3+}} - \frac{RT}{nF}\ln\frac{\ce{[Fe^{2+}]}}{\ce{[Fe^{3+}]}}$$</span> </p> <p><span class="math-container">$$E = E^\circ_\ce{Cr^{6+}/Cr^{3+}} - \frac{RT}{nF}\ln\frac{\ce{[Cr^{3+}]}}{\ce{[Cr^{6+}]}}$$</span></p> <p>Adding both the above equations, we get</p> <p><span class="math-container">$$2E = E^\circ_\ce{Fe^{2+}/Fe^{3+}} + E^\circ_\ce{Cr^6+/Cr^3+} - \frac{RT}{nF}ln\frac{\ce{[Fe^{2+}][Cr^{3+}]}}{\ce{[Fe^{3+}][Cr^{6+}]}}$$</span> </p> <p>Since <span class="math-container">$\ce{[Fe^2+]=[Cr^6+]}$</span> and <span class="math-container">$\ce{[Fe^3+]=[Cr^3+]}$</span></p> <p>They would all be getting cancelled, ending in</p> <p><span class="math-container">$$E = \frac{E^\circ_\ce{Fe^{2+}/Fe^{3+}} + E^\circ_\ce{Cr^{6+}/Cr^{3+}}}{2}$$</span></p> <p>But, at equivalence point, the titrant ions would have entirely reduced and the titrand ions would have entirely oxidised, leaving</p> <p><span class="math-container">$$\ce{[Fe^{2+}]=[Cr^{6+}]}=0$$</span> </p> <p>And as we know, in mathematics, <span class="math-container">$\frac00$</span> is infinite or not defined. So, how do can we actually mathematically derive the electrode potential at the equivalence point?</p>