Question

Standard reduction potentials of some elements are given below.

Al = – 1.66 V, Cd = – 0.40 V, Ag = + 0.80 V & Au = + 1.36 V

1. Which of these can displace hydrogen from hydrochloric acid. Why?

2. Construct a galvanic cell using any two electrodes. Write the cell reaction and calculate the standard emf.

Answer 1

1. Al and Cd can displace hydrogen from HCl. Metals with low reduction potential than H (i.e., with -ve value) can liberate H₂ from acids.

2.

At Anode - (Oxidation),

Cd →Cd²⁺ +2\(\bar e\)

At Cathode - (Reduction),

2Ag⁺ + 2\(\bar e\) → 2Ag

∴ Cell reaction, 

Cd + 2Ag⁺ → cd²⁺ +2Ag

E⁰_cell = E⁰_cathode - E⁰_Anode

= 0.80 V -(-0.40V) = 1.2V