⚡ Electrochemistry Master

🧪 OIL RIG (oxidation loss, reduction gain) 🔋 Anode negative in galvanic cell ⚡ Cathode: reduction always 🧴 Fuel cell → H₂O

💡TIP Mn in K₂MnO₄ = +6 (potassium manganate) 🧠TRICK “LEO the lion says GER” 📝NOTE Conc. NaCl → Cl₂ at anode

📋 Multiple Choice Questions

🔖 Short Answer Questions (B)

16.1

What happens when electricity is passed through an aqueous solution of NaCl?

H₂ at cathode, Cl₂ at anode (concentrated); dilute gives O₂.

16.2

Main objectives of electroplating?

Prevent corrosion, decorate, improve wear resistance.

16.3

Difference: electrolytic vs galvanic cell?

Electrolytic: external voltage drives reaction. Galvanic: spontaneous produces electricity.

16.4

Through which electrode do electrons leave the electrolytic cell?

Anode (electrons leave cell to external circuit).

16.5

How does an electrolyte conduct electricity?

Ions move to electrodes and discharge.

16.6

Cu strip dipped in FeSO₄ solution?

No reaction because Cu is below Fe in reactivity series.

16.7

Why fuel cells are environment friendly?

By-product mainly water, low pollutants.

📌 Constructed Response (C)

16.1

Oxidation number Cl in Ca(ClO₄)₂?

Ca = +2, O = -2×8 = -16 → total Cl₂ = +14 → each Cl = +7.

16.2

How H₂O₂ behaves as oxidizing agent?

H₂O₂ gains electrons → reduced to H₂O or OH⁻.

16.3

Why different products dilute vs conc. NaCl?

Dilute: OH⁻ oxidation gives O₂; conc: Cl⁻ oxidation gives Cl₂.

16.4

Corrosion fast during rainy season?

Humidity + electrolytes (ions) accelerate electrochemical rusting.

16.5

Galvanic cell Cu and Ag: reactions?

Anode Cu → Cu²⁺ + 2e⁻; Cathode Ag⁺ + e⁻ → Ag.

16.6

Function of porous partition?

Prevents mixing while allowing ion flow to maintain neutrality.

16.7

How fuel cells produce electricity?

H₂ oxidized at anode, O₂ reduced at cathode; produce H₂O and flow e⁻.

16.8

Compare reactivity by electrochemical series?

Higher E° reduction means weaker reducing agent; more reactive metals have low E°red.

📚 Descriptive D (key points)

16.1 Ionic formula using oxidation numbers: e.g. Al³⁺ & O²⁻ → Al₂O₃.
16.2 Al(NO₃)₃: N=+5 ; H₂SO₄: S=+6 ; Na₂S₂O₃: S=+2 (avg).
16.3 Sodium hypochlorite NaClO, calcium oxalate CaC₂O₄, ammonium phosphate (NH₄)₃PO₄, calcium nitrite Ca(NO₂)₂.
16.4-16.7 Working of fuel cell: H₂ → 2H⁺ + 2e⁻ at anode, O₂ + 4e⁻ + 4H⁺ → 2H₂O. Electrolysis of conc. metal halides: halogen at anode. Electroplating uses CuSO₄ with Cu anode. Corrosion of iron: Fe → Fe²⁺ + 2e⁻ (anodic), O₂ + 2H₂O + 4e⁻ → 4OH⁻ (cathodic).