Error 1: Reversing E°cell Formula

Wrong: E°cell = E°anode − E°cathode Correct: E°cell = E°cathode − E°anode Impact: Gives wrong sign; if both potentials are given and student subtracts in wrong order, they get −1.10 V instead of +1.10 V for Daniell cell. Fix: Always write "C minus A" = Cathode minus Anode. Cathode is the RIGHT side of cell notation.

Error 2: Using Minutes Instead of Seconds in Faraday's Law

Wrong: w = MIt/(nF) with t = 60 (min) for a 1-hour electrolysis Correct: t must be in SECONDS. 1 hour = 3600 s. Impact: Answer will be 60× too small. Fix: Always convert time to seconds before substituting in w = MIt/(nF).

Error 3: Wrong n for Copper Electrolysis

Wrong: Using n = 1 for $CuSO_{4}$ (confusing with $AgNO_{3}$) Correct: $Cu^{2+}$ + 2$e^{-}$ → Cu requires n = 2. Impact: Answer doubled (too large). In contrast, $Ag^{+}$ + $e^{-}$ → Ag uses n = 1. Fix: Write the half-reaction and count electrons explicitly every time.

Error 4: Galvanic vs Electrolytic Anode Polarity

Wrong: Assuming anode is always negative Correct: Anode is negative ONLY in galvanic cells; anode is POSITIVE in electrolytic cells. Impact: Incorrect identification of electrodes in electrolytic/industrial applications. Fix: Remember "GANE" mnemonic — Galvanic Anode Negative; Electrolytic is opposite.

Error 5: Wrong Q Expression in Nernst Equation

Wrong: Writing Q as [products]/[reactants] without identifying correct oxidized and reduced species. Correct: Q = [oxidized form products]/[reduced form reactants], matching the specific cell reaction. Example: For Zn + $Cu^{2+}$ → $Zn^{2+}$ + Cu: Q = [$Zn^{2+}$]/[$Cu^{2+}$] (solid Zn and Cu not included) Impact: Wrong log term → wrong EMF calculation.

Error 6: Applying Strong-Electrolyte Extrapolation to Weak Electrolytes

Wrong: Extrapolating Λm vs. √C graph for $CH_{3}COOH$ to get Λ°m Correct: Use Kohlrausch's law (sum of ionic conductivities from strong electrolyte data) Impact: Significantly incorrect Λ°m value due to non-linear curve for weak electrolytes. Fix: For weak electrolytes, Λ°m is CALCULATED, not graphically determined.

Error 7: Confusing Oxidation and Reduction of $OF_{2}$

Wrong: Assigning O = −2 in $OF_{2}$ (applying default rule) Correct: O = +2 in $OF_{2}$ (F is more electronegative, always −1) Impact: Wrong balance of oxidation numbers.

Error 8: Forgetting ν in Kohlrausch's Law

Wrong: Λ°m($MgCl_{2}$) = λ°($Mg^{2+}$) + λ°($Cl^{-}$) Correct: Λ°m($MgCl_{2}$) = λ°($Mg^{2+}$) + 2λ°($Cl^{-}$) [ν₋ = 2 for $MgCl_{2}$] Impact: Off by a multiple of the stoichiometric number. Fix: Write the dissociation equation first: $MgCl_{2}$ → $Mg^{2+}$ + 2$Cl^{-}$, then apply Kohlrausch.