HardChemistryHigh School (11–12)The p-Block ElementsNumericalConceptual

Thallium forms a compound with the formula TlI₃…

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Thallium forms a compound with the formula TlI $_3$ . If it contained Tl $^{3+}$ and three iodide ions, the Tl $^{3+}$ would oxidise iodide: $\text{Tl}^{3+} + 2\text{I}^{-} \to \text{Tl}^{+} + \text{I}_{2}$ . The standard potential is $+1.25\ \text{V}$ for Tl $^{3+}$ changing to Tl $^+$ and $+0.54\ \text{V}$ for I $_2$ changing to I $^-$ . Find the cell potential and $\log K$ for the reaction at 298 K. Then say what oxidation state thallium has in the compound, if the iodine forms the ion I $_3^-$ .

Need a reminder? The key ideaShow

For a redox reaction, $E^\circ_{cell} = E^\circ_{ox} - E^\circ_{red}$ , $\Delta G^\circ = -nFE^\circ_{cell}$ with $F = 96.485\ \text{kJ/(V mol)}$ , and at 298 K, $\log K = \dfrac{nE^\circ_{cell}}{0.05916\ \text{V}}$ . A reaction goes if $E^\circ_{cell}$ is positive. Moles of reactant come from mass divided by molar mass, and the equation gives the ratios.

The worked solution

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