How many moles of electrons are transferred when 1 mole of $Cr_2O_7^{2-}$ is reduced to $Cr^{3+}$ in acidic solution?

In Cr₂O₇²⁻, chromium has an oxidation state of +6. Each Cr is reduced from +6 to +3, a change of 3 electrons per chromium atom. Since there are 2 chromium atoms in one dichromate ion, the total electrons transferred = 2 × 3 = 6 moles of electrons. The balanced half-equation is: Cr₂O₇²⁻ + 14H⁺ + 6e⁻ → 2Cr³⁺ + 7H₂O.