Electrochemistry

🟢 Lite — Quick Review (1h–1d)

Rapid summary for last-minute revision before your exam.

Electrochemistry — Key Facts Galvanic cell: spontaneous redox reaction generates electricity; anode = negative, cathode = positive Electrolytic cell: electricity drives non-spontaneous reaction; anode = positive, cathode = negative Standard hydrogen electrode (SHE): $E° = 0$ V by definition; used as reference Cell EMF: $E°{cell} = E°{cathode} - E°_{anode}$ ⚡ Exam tip: In electrolytic cells, cations go to cathode (negative); anions go to anode (positive) — opposites attract

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🟡 Standard — Regular Study (2d–2mo)

Standard content for students with a few days to months.

Electrochemistry — JAMB Chemistry Study Guide Standard electrode potentials (25°C): $Na^+ + e^- \rightarrow Na$: $E° = -2.71$ V $Al^{3+} + 3e^- \rightarrow Al$: $E° = -1.66$ V $Zn^{2+} + 2e^- \rightarrow Zn$: $E° = -0.76$ V $Fe^{2+} + 2e^- \rightarrow Fe$: $E° = -0.44$ V $Cu^{2+} + 2e^- \rightarrow Cu$: $E° = +0.34$ V $Ag^+ + e^- \rightarrow Ag$: $E° = +0.80$ V $Au^{3+} + 3e^- \rightarrow Au$: $E° = +1.50$ V

Predicting spontaneity: If $E°{cell} > 0$, reaction is spontaneous; if $E°{cell} < 0$, non-spontaneous.

Faraday’s laws of electrolysis: First law: mass $m = \frac{Q}{F} \times \frac{M}{n} = \frac{It}{F} \times \frac{M}{n}$ Second law: same quantity of electricity produces same moles of electrons, so different masses proportional to $M/n$. Where: $F = 96,485$ C/mol, $M$ = molar mass, $n$ = electrons transferred, $I$ = current (A), $t$ = time (s).

⚡ Exam tip: 1 Faraday = 96,485 C = charge on 1 mole of electrons; 1 ampere = 1 C/s.

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🔴 Extended — Deep Study (3mo+)

Comprehensive coverage for students on a longer study timeline.

Electrochemistry — Comprehensive Chemistry Notes

Daniell cell (Zn-Cu cell): $Zn(s) | Zn^{2+}(aq) || Cu^{2+}(aq) | Cu(s)$ Anode (oxidation): $Zn(s) \rightarrow Zn^{2+}(aq) + 2e^-$ ($E° = -0.76$ V) Cathode (reduction): $Cu^{2+}(aq) + 2e^- \rightarrow Cu(s)$ ($E° = +0.34$ V) $E°_{cell} = 0.34 - (-0.76) = 1.10$ V

Concentration cells: Same electrodes in solutions of different concentrations. $E = E° - \frac{0.059}{n}\log Q$ at 25°C. At equilibrium ($Q = K_{eq}$), $E = 0$.

Electrolytic cells — products: For molten salts (e.g., NaCl molten): $Na^+$ reduced at cathode → Na; $Cl^-$ oxidised at anode → Cl₂. For aqueous solutions: water may be preferentially reduced/oxidised depending on $E°$ values. $2H_2O + 2e^- \rightarrow H_2 + 2OH^-$ ($E° = -0.83$ V) $2H_2O \rightarrow O_2 + 4H^+ + 4e^-$ ($E° = -1.23$ V) For dilute NaCl: $H_2$ produced at cathode (since $E°_{Na/Na^+} = -2.71$ is more negative than water’s); $Cl_2$ produced at anode (overpotential considerations).

Commercial cells: Primary cells: cannot be recharged (e.g., dry cell, Leclanche: $Zn | NH_4Cl | MnO_2 | C$) Secondary cells: rechargeable (e.g., lead-acid battery: $Pb | H_2SO_4 | PbO_2$) Fuel cells: $H_2 + O_2 \rightarrow H_2O$ with electrodes and electrolyte (e.g., KOH); efficient, low pollution.

Quantitative electrolysis: For $CuSO_4$ solution with Cu electrodes: Cathode: $Cu^{2+} + 2e^- \rightarrow Cu$ (pure copper deposited) Anode: $Cu \rightarrow Cu^{2+} + 2e^-$ (copper dissolves) Net: no net chemical change; acts as electrolytic purification. For $CuSO_4$ with Pt electrodes: $Cu^{2+}$ reduced at cathode; $OH^-$ oxidised at anode → $O_2$ (since $E°{O_2/H_2O} = +1.23$ vs $E°{S_2O_8^{2-}/SO_4^{2-}} = +2.01$, actually $SO_4^{2-}$ is harder to oxidise).

JAMB exam patterns:

• 2023 JAMB: Calculate mass of Ag deposited when 1 F of electricity passes through $AgNO_3$ solution
• 2022 JAMB: In the electrolysis of $NaCl$ solution, identify product at cathode and anode
• 2021 JAMB: Given $E°{Zn/Zn^{2+}} = -0.76$ V and $E°{Cu/Cu^{2+}} = +0.34$ V, calculate cell EMF
• 2020 JAMB: Why does stainless steel not corrode like ordinary steel?

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📊 JAMB Exam Essentials

Detail	Value
Questions	180 MCQs (UTME)
Subjects	4 subjects (language + 3 for course)
Time	2 hours
Marking	+1 per correct answer
Score	400 max (used for university admission)
Registration	January – February each year

🎯 High-Yield Topics for JAMB

• Use of English (Grammar + Comprehension) — 60 marks
• Biology for Science students — 40 marks
• Chemistry (Organic + Physical) — 40 marks
• Physics (Mechanics + Optics) — 35 marks
• Mathematics (Algebra + Geometry) — 40 marks

📝 Previous Year Question Patterns

• Q: “The process of photosynthesis requires…” [2024 Biology]
• Q: “The electronic configuration of Fe is…” [2024 Chemistry]
• Q: “Find the value of x if 2x + 5 = 15…” [2024 Mathematics]

💡 Pro Tips

• Use of English carries the most weight — master grammar rules and comprehension strategies
• JAMB syllabus is your Bible — questions come directly from it. Download and use it.
• Past questions are highly predictive — repeat patterns appear every year
• For Science students, Biology and Chemistry are high-scoring if you study NCERT-level content

🔗 Official Resources

• JAMB Official
• JAMB Syllabus

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