Waec Model Questions Vol1 2020 Chemistry Question 49

Practice objective / multiple choice question 49 from the 2020 Waec Model Questions Vol1 Chemistry examination.

Waec Model Questions Vol1 2020 Chemistry Objective / Multiple Choice Hard Difficulty
Question 49 WAEC_MODEL_QUESTIONS_VOL1 • 2020 • CHEMISTRY • objective

A galvanic cell is set up with an iron electrode in 0.010 M Fe²⁺ solution and a copper electrode in 0.010 M Cu²⁺ solution, connected by a salt bridge. Standard reduction potentials are: Fe²⁺ + 2e⁻ → Fe, E° = -0.44 V; Cu²⁺ + 2e⁻ → Cu, E° = +0.34 V. (a) Write the overall cell reaction and calculate the standard cell EMF (E°cell). (b) Using the Nernst equation at 25 °C, find the cell EMF for the given concentrations. (c) If the iron electrode is coated with a thin layer of zinc (Zn²⁺ + 2e⁻ → Zn, E° = -0.76 V), will the zinc coating protect the iron from corrosion in this cell? Justify with potentials.

Answer Options

Correct Answer A. Fe(s)+Cu²⁺→Fe²⁺+Cu(s); 0.78 V; 0.78 V; Yes, Zn protects Fe because it is more easily oxidised (E° = -0.76 V) and acts as a sacrificial anode.
B. Fe(s)+Cu²⁺→Fe²⁺+Cu(s); 0.68 V; 0.68 V; No, Zn does not protect Fe because its standard potential is more negative than Fe, so it will not act as a sacrificial anode.
C. Fe(s)+Cu²⁺→Fe²⁺+Cu(s); 0.78 V; 0.75 V; Yes, Zn protects Fe because its potential is more negative, making it a sacrificial anode, although the calculated cell EMF is slightly lower than the standard value.
D. Cu(s)+Fe²⁺→Cu²⁺+Fe(s); 0.78 V; 0.78 V; No, Zn would accelerate corrosion of Fe since Zn is less noble and will preferentially dissolve.
Correct Answer
A
Correct Option:
Fe(s)+Cu²⁺→Fe²⁺+Cu(s); 0.78 V; 0.78 V; Yes, Zn protects Fe because it is more easily oxidised (E° = -0.76 V) and acts as a sacrificial anode.

About This Question

This is Waec Model Questions Vol1 2020 Chemistry Question 49. It is one of the objective questions from the 2020 Waec Model Questions Vol1 Chemistry examination.

Difficulty level: Hard .

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